Resistance of Selected Sorghum Genotypes to Maize Weevil (Coleoptera: Curculionidae)

Resistance of Selected Sorghum Genotypes to Maize Weevil (Coleoptera: Curculionidae) Abstract The maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), is a major insect pest of stored grain. This study evaluated resistance of grain of 26 sorghum genotypes, Sorghum bicolor (L.) Moench, to maize weevil under laboratory conditions. Three female and two male newly emerged maize weevils were reared with 5 g of grain in each of 10 vials for each of the 26 sorghum genotypes in a laboratory experiment. The weevils and grain of each genotype were scored once every 3 wk for a total of five times during 105 d. The numbers of live and newly emerged maize weevils, dead weevils from the initial population, damage score (scale of 1–5), and grain weight loss were used to indicate resistance. The least percentage weight loss of 23.9 and 24.1% was recorded for sorghum genotypes Sureño and (5BRON151*Tegemeo)-HG7, respectively. Genotypes B.HF8 and (A964*P850029)-HW6 had the most weight loss, 70.6 and 67.7%, at 105 d after infestation. Genotypes B.HF8 and (A964*P850029)-HW6 consistently exhibited the highest numbers of maize weevil, 63 and 84, per vial at 105 d after infestation. Sorghum genotypes Sureño, (SV1*Sima/IS23250)-LG15, (5BRON151*Tegemeo)-HG7, and (B35*B9501)-HD9 ranked among the top four genotypes with least damage rating more often than any other genotype across the five sampling dates. On the other hand, genotypes B.HF8, (A964*P850029)-HW6, (Segaolane*WM#322)LG2, and (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1 were more often ranked among the top four genotypes with the highest damage rating. Our results indicate that grain of genotype Sureno is most resistant to the maize weevil among screened genotypes. Sitophilus, zeamais, Sorghum, bicolor, resistance The maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), is one of the most destructive and widely distributed primary insect pests of stored grain (Teetes et al. 1981, Throne 1994). It is primarily associated with maize, Zea mays L., but can develop on all cereal grains and cereal products (Walgenbach and Burkholder 1986, Tipping et al. 1987). Hosts of maize weevil include barley, Hordeum vulgare L., maize, oats, Avena sativa L., sorghum, Sorghum bicolor L. and wheat, Triticum sp. L. (Morrison 1963). The common sources of stored grain pests are grain spills, old grain, seed, feeds, and grain debris. Insects often move from carryover grain, uncleaned empty bins, feed supply buildings, and grain debris beneath perforated bin floors into grain newly put into storage. Maize weevil can also infest developing kernels in the field (Caswell 1961, Vyavhare 2010, Vyavhare and Pendleton 2011) and are taken into storage where they continue to live and damage stored grain. The adult maize weevil lives an average of 2 to 5 mo, and each female lays about 300 to 400 eggs during this period (Morrison 1963). The female chews small cavities into kernels and lays eggs individually. She seals the cavities with a sticky secretion from her anus. Eggs hatch in 6 d and the larvae feed inside the grain. After passing through four instars, the larvae pupate inside the grain. The life cycle averages 39 d under optimal conditions (Morrison 1963, Wilbur and Mills 1985). Adults and larvae feed on grain, with major damage by larvae developing inside kernels. Because the insects feed inside grain, they and their excreta are ground along with grain during milling. Infestation by maize weevils reduces the quality and viability of seed and seedling vigor. Fungi grow on the insect exuvia and excreta. The presence of insects also reduces the commercial value of the grain. Worldwide sorghum grain losses to maize weevil and other stored grain pests can range from 15 to 77% (Nyambo 1993, Ramputh et al. 1999, Goftishu and Belete 2014). Grain losses to maize weevil are more pronounced in the tropical and subtropical agroecosystems where environmental factors are conducive for the reproduction and development of weevils, and where storage facilities are inadequate (Tigar et al. 1994, Goftishu and Belete 2014). Many practices are used to protect grain from storage insects. Cultural management practices include sanitation, drying, cleaning, and aeration (Allotey 1991). Cultural practices help to reduce grain losses only to a certain extent because internal infestation and contamination cannot all be removed by ordinary cultural practices such as cleaning. Synthetic insecticides are one of the widely used control measures against storage pests, but the use of persistent and wide-spectrum organochlorine and some organophosphate compounds has led to health and environmental concerns (Markowitz 1992). In addition, use of synthetic insecticides poses high risk of development of resistance in insect populations and nontarget effects (Zettler and Cuperus 1990, Bekele et al. 1997). For instance, a global survey of susceptibility of stored grain pests to insecticides showed widespread resistance by major stored grain insect pests to malathion and lindane (Champ and Dyte 1976). This necessitates searching for alternative management tactics that are effective, economical, and environment friendly. Insect-resistant cultivars are an important component of integrated pest management. The use of resistant or less susceptible cultivars integrated with other sustainable pest control methods can provide a longer lasting solution to losses in storage (Dobie 1977). Resistance of sorghum to various insect pests in the field has been studied by many researchers (Agrawal et al. 1990, Nwanze et al. 1991), but resistance to stored-grain pests has been one of the neglected areas of sorghum entomology. The current study was conducted with the objective to evaluate resistance of 26 genotypes of sorghum to maize weevil under laboratory conditions. Materials and Methods The grain of 26 genotypes of sorghum was evaluated for resistance to maize weevil under laboratory conditions at West Texas A&M University, Canyon, TX. Table 1 lists the 26 genotypes used in the experiment. The grain of all genotypes was obtained from the Sorghum Improvement Program at the Texas A&M AgriLife Research and Extension Center in Lubbock, TX. Table 1. List of sorghum genotypes evaluated for resistance to maize weevil No.  Pedigree  Reasoning  1  Sureño  Line developed and released for improved grain quality and resistance to grain mold/weathering  2  Macia  Introduction from Southern Africa with improved grain quality  3  CE151  Introduction from Senegal with preflowering drought tolerance and resistance to sugarcane aphid  4  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864 *PI550607)))))-PR3-CM3  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  5  (B35*B9501)-HD9  Germplasm developed with resistance to postflowering drought stress  6  B409  Germplasm developed with resistance to postflowering drought stress  7  B.HF8  Germplasm developed with resistance to postflowering drought stress  8  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  9  VG153*(TAM428*SBIII)-23  Germplasm developed for improved grain quality  10  (85OG4300-5*Tx2782)-SM5  Germplasm developed for resistance to sorghum midge  11  (M84-7*VG153)-LBK  Germplasm developed for improved grain quality  12  (9MLT176*A964)-CA3  Germplasm developed for resistance to sorghum midge  13  (9MLT176*A964)-LG8  Germplasm developed for resistance to sorghum midge  14  (Dorado*Tegemeo)-HW13  Germplasm developed for improved grain quality  15  (Dorado*Tegemeo)-HW14  Germplasm developed for improved grain quality  16  (Dorado*Tegemeo)-HW15  Germplasm developed for improved grain quality  17  (A964*P850029)-HW6  Germplasm developed for improved adaptation  18  Tegemeo  Introduction from Southern Africa with improved grain quality and adaptation  19  (5BRON151*Tegemeo)-HG1  Germplasm developed for improved grain quality  20  (5BRON151*Tegemeo)-HG7  Germplasm developed for improved grain quality  21  (Kuyuma*5BRON155)-CA5  Germplasm developed for improved grain quality  22  (Macia*TAM428)-LL9  Germplasm developed for resistance to sugarcane aphid in South Africa  23  (SV1*Sima/IS23250)-LG15  Germplasm developed for resistance to sugarcane aphid in South Africa  24  (Segaolane*WM#322)-LG2  Germplasm developed for resistance to sugarcane aphid in South Africa  25  (6BRON161*CE151)-LG5  Germplasm developed for resistance to sugarcane aphid in South Africa  26  (Macia*TAM428)-LL2  Germplasm developed for resistance to sugarcane aphid in South Africa  No.  Pedigree  Reasoning  1  Sureño  Line developed and released for improved grain quality and resistance to grain mold/weathering  2  Macia  Introduction from Southern Africa with improved grain quality  3  CE151  Introduction from Senegal with preflowering drought tolerance and resistance to sugarcane aphid  4  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864 *PI550607)))))-PR3-CM3  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  5  (B35*B9501)-HD9  Germplasm developed with resistance to postflowering drought stress  6  B409  Germplasm developed with resistance to postflowering drought stress  7  B.HF8  Germplasm developed with resistance to postflowering drought stress  8  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  9  VG153*(TAM428*SBIII)-23  Germplasm developed for improved grain quality  10  (85OG4300-5*Tx2782)-SM5  Germplasm developed for resistance to sorghum midge  11  (M84-7*VG153)-LBK  Germplasm developed for improved grain quality  12  (9MLT176*A964)-CA3  Germplasm developed for resistance to sorghum midge  13  (9MLT176*A964)-LG8  Germplasm developed for resistance to sorghum midge  14  (Dorado*Tegemeo)-HW13  Germplasm developed for improved grain quality  15  (Dorado*Tegemeo)-HW14  Germplasm developed for improved grain quality  16  (Dorado*Tegemeo)-HW15  Germplasm developed for improved grain quality  17  (A964*P850029)-HW6  Germplasm developed for improved adaptation  18  Tegemeo  Introduction from Southern Africa with improved grain quality and adaptation  19  (5BRON151*Tegemeo)-HG1  Germplasm developed for improved grain quality  20  (5BRON151*Tegemeo)-HG7  Germplasm developed for improved grain quality  21  (Kuyuma*5BRON155)-CA5  Germplasm developed for improved grain quality  22  (Macia*TAM428)-LL9  Germplasm developed for resistance to sugarcane aphid in South Africa  23  (SV1*Sima/IS23250)-LG15  Germplasm developed for resistance to sugarcane aphid in South Africa  24  (Segaolane*WM#322)-LG2  Germplasm developed for resistance to sugarcane aphid in South Africa  25  (6BRON161*CE151)-LG5  Germplasm developed for resistance to sugarcane aphid in South Africa  26  (Macia*TAM428)-LL2  Germplasm developed for resistance to sugarcane aphid in South Africa  View Large Table 1. List of sorghum genotypes evaluated for resistance to maize weevil No.  Pedigree  Reasoning  1  Sureño  Line developed and released for improved grain quality and resistance to grain mold/weathering  2  Macia  Introduction from Southern Africa with improved grain quality  3  CE151  Introduction from Senegal with preflowering drought tolerance and resistance to sugarcane aphid  4  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864 *PI550607)))))-PR3-CM3  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  5  (B35*B9501)-HD9  Germplasm developed with resistance to postflowering drought stress  6  B409  Germplasm developed with resistance to postflowering drought stress  7  B.HF8  Germplasm developed with resistance to postflowering drought stress  8  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  9  VG153*(TAM428*SBIII)-23  Germplasm developed for improved grain quality  10  (85OG4300-5*Tx2782)-SM5  Germplasm developed for resistance to sorghum midge  11  (M84-7*VG153)-LBK  Germplasm developed for improved grain quality  12  (9MLT176*A964)-CA3  Germplasm developed for resistance to sorghum midge  13  (9MLT176*A964)-LG8  Germplasm developed for resistance to sorghum midge  14  (Dorado*Tegemeo)-HW13  Germplasm developed for improved grain quality  15  (Dorado*Tegemeo)-HW14  Germplasm developed for improved grain quality  16  (Dorado*Tegemeo)-HW15  Germplasm developed for improved grain quality  17  (A964*P850029)-HW6  Germplasm developed for improved adaptation  18  Tegemeo  Introduction from Southern Africa with improved grain quality and adaptation  19  (5BRON151*Tegemeo)-HG1  Germplasm developed for improved grain quality  20  (5BRON151*Tegemeo)-HG7  Germplasm developed for improved grain quality  21  (Kuyuma*5BRON155)-CA5  Germplasm developed for improved grain quality  22  (Macia*TAM428)-LL9  Germplasm developed for resistance to sugarcane aphid in South Africa  23  (SV1*Sima/IS23250)-LG15  Germplasm developed for resistance to sugarcane aphid in South Africa  24  (Segaolane*WM#322)-LG2  Germplasm developed for resistance to sugarcane aphid in South Africa  25  (6BRON161*CE151)-LG5  Germplasm developed for resistance to sugarcane aphid in South Africa  26  (Macia*TAM428)-LL2  Germplasm developed for resistance to sugarcane aphid in South Africa  No.  Pedigree  Reasoning  1  Sureño  Line developed and released for improved grain quality and resistance to grain mold/weathering  2  Macia  Introduction from Southern Africa with improved grain quality  3  CE151  Introduction from Senegal with preflowering drought tolerance and resistance to sugarcane aphid  4  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864 *PI550607)))))-PR3-CM3  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  5  (B35*B9501)-HD9  Germplasm developed with resistance to postflowering drought stress  6  B409  Germplasm developed with resistance to postflowering drought stress  7  B.HF8  Germplasm developed with resistance to postflowering drought stress  8  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  9  VG153*(TAM428*SBIII)-23  Germplasm developed for improved grain quality  10  (85OG4300-5*Tx2782)-SM5  Germplasm developed for resistance to sorghum midge  11  (M84-7*VG153)-LBK  Germplasm developed for improved grain quality  12  (9MLT176*A964)-CA3  Germplasm developed for resistance to sorghum midge  13  (9MLT176*A964)-LG8  Germplasm developed for resistance to sorghum midge  14  (Dorado*Tegemeo)-HW13  Germplasm developed for improved grain quality  15  (Dorado*Tegemeo)-HW14  Germplasm developed for improved grain quality  16  (Dorado*Tegemeo)-HW15  Germplasm developed for improved grain quality  17  (A964*P850029)-HW6  Germplasm developed for improved adaptation  18  Tegemeo  Introduction from Southern Africa with improved grain quality and adaptation  19  (5BRON151*Tegemeo)-HG1  Germplasm developed for improved grain quality  20  (5BRON151*Tegemeo)-HG7  Germplasm developed for improved grain quality  21  (Kuyuma*5BRON155)-CA5  Germplasm developed for improved grain quality  22  (Macia*TAM428)-LL9  Germplasm developed for resistance to sugarcane aphid in South Africa  23  (SV1*Sima/IS23250)-LG15  Germplasm developed for resistance to sugarcane aphid in South Africa  24  (Segaolane*WM#322)-LG2  Germplasm developed for resistance to sugarcane aphid in South Africa  25  (6BRON161*CE151)-LG5  Germplasm developed for resistance to sugarcane aphid in South Africa  26  (Macia*TAM428)-LL2  Germplasm developed for resistance to sugarcane aphid in South Africa  View Large Maize weevils were cultured on popcorn seeds in 0.95-liter glass jars in the laboratory. To ensure enough newly emerged maize weevils to infest grain of the genotypes, six jars were maintained with popcorn and live maize weevils. The top of each jar was covered by a piece of organdy cloth under the metal jar ring screwed onto the top. The jars of maize weevils were maintained at 25–27°C and 70% relative humidity. Popcorn was added to each jar regularly to ensure enough food for the maize weevil colony. Prior to the beginning of experiment, grain of all genotypes was kept at room temperature (25–27°C) and relative humidity of 65–70% for 10 d to bring the equilibrium moisture content of grain to ~14%. Weight of individual sorghum kernels was measured to relate it to damage caused by maize weevils. One gram of grain of each of sorghum genotype was weighed, and the number of grains per gram was counted. Five replications were used of each of the genotypes to count the number of kernels per gram. The weight of 100 kernels was determined for each sorghum genotype. Between 6 June and 21 November 2009, grains of 26 genotypes of sorghum (Table 1) were evaluated for resistance to maize weevil. Ten plastic 20-ml scintillation vials were used for each genotype of sorghum. Three female and two male maize weevils that emerged that day from a colony maintained on popcorn were placed into each of 10 vials with 5 g of grain of a genotype. Intact whole grains were chosen for the experiment. The initial five weevils were marked with white correction fluid (Liquid Paper, Bellwood, IL) on the day of infestation of each genotype to distinguish the initial weevils from their progeny. Each day newly emerged maize weevils were obtained by pouring the weevils and popcorn from the jars into a sieve (4-mm diameter) that allowed the weevils to pass through the holes in the sieve and collect on a paper plate set on a chilling table (Laboratory Chill Table Model# 1431, BioQuip Products, Rancho Dominguez, CA) to cool the weevils and prevent them from flying away. The maize weevils were put into Petri dishes. A dissecting microscope was used to aid in determining the gender of the weevils. A male maize weevil has a shorter, thicker, and rougher snout than a female (Wilbur and Mills 1985). Also, when viewed in profile, the tip of the abdomen of a male maize weevil curves downward while that of a female extends straight back. Each vial with sorghum grain was closed by a small piece of organdy cloth tied over the top of the vial by a small rubber band. Each day, a set of 10 vials of each genotype was set up. Ten vials represented 10 replications for each genotype/treatment. The experimental design was completely randomized with the vials placed randomly. The vials were placed on a table with a 15.1-liter ultrasonic humidifier (Holmes Air, Model HM-600, Holmes Products Corporation, MA) under a plastic-covered cage to maintain relative humidity at approximately 65–70% and temperature at 25–27°C throughout the experiment. The study was carried out under natural photoperiod. The maize weevils and grain in each of the 10 vials of each genotype were scored once every 3 wk for a total of five times during 105 d after the grain in the vials had been infested with weevils. During 105 d, the maize weevils fed on the grain, mated, and laid eggs to produce new progeny. Each day 10 vials of maize weevils and grain of one genotype were observed and returned to the covered cage. Maize weevils and sorghum grains were poured into a Petri dish on ice to collect adults. A camel-hair brush was used to sort the maize weevils from the grain. The grain was put back into the vial and weighed. After weighing, the grain was placed on a dish, and each kernel examined with the aid of a dissecting microscope to determine the amount of damage. A scale of 1 to 5 was used to score damage by maize weevils to the grain, where 1 = no evidence of feeding; 2 = some feeding such as one hole on the surface but not all the way through the grain (1–25% of the grain damaged); 3 = two tunnels through the grain (26–50% damaged); 4 = more than two holes and/or grain was 51–75% damaged; and 5 = many feeding tunnels in grain (76–100% damaged). The weevils collected in the Petri dishes set on the chilling table were observed with the aid of a dissecting microscope. The numbers of live and dead weevils were counted in each of the 10 vials. After observation, the live weevils were returned to the vial with the sorghum grain, and the top of the vial was covered by organdy cloth fastened by a rubber band. At each observation period, the number of live weevils, number of dead weevils of the initial marked population, damage score, and weight of the grain were recorded. Data were analyzed by analysis of variance (ANOVA) using Agricultural Research Manager Program (GDMInc. 2017). After initial analysis, data were transformed using square root of X + 0.5 to meet the homogeneity of variance assumption of ANOVA. Multiple comparisons among treatment means were determined using Student–Newman–Keuls test. Percent grain weight loss for treatments was calculated using the formula: [(initial weight (5 g) − final weight excluding weevils)/initial weight] × 100. In addition to the overall ANOVA, correlation and regression analyses were used to examine relationship between kernel weight and number of live weevils, kernel weight and damage score, and kernel weight and grain weight loss at 105 d after infestation. The best-fit models were selected from linear, quadratics, and cubic models on the basis of R2 values. All statistical differences were determined using α level 0.05. Results Number of Weevils The total number of live maize weevils per vial at 63 (F = 6.86; df = 25, 229; P = 0.0001), 84 (F = 5.24; df = 25, 229; P = 0.0001), and 105 (F = 4.41; df = 25, 229; P = 0.0001) d after infestation differed significantly among the 26 genotypes of sorghum (Table 2). Genotypes B.HF8 and (A964*P850029)-HW6 consistently showed highest numbers of maize weevil per vial at 63, 84, and 105 d after infestation. Fewest maize weevils were in grain of (SV1*Sima/IS2325)-LG15 at 63 and 84 d after infestation and Sureño at 105 d after infestation. Table 2. Mean number of live maize weevils per vial at 63, 84, and 105 d after infestation Sorghum genotype*  Number of live weevils† per vial days after infestation of grain  63 d  84 d  105 d  1  23.70gh  32.80e  35.30d  2  37.20c–h  53.70cde  60.70bcd  3  49.30b–g  70.60be  90.40a–d  4  59.70a–f  80.40a–d  92.00a–d  5  30.20d–h  39.00de  38.50d  6  61.20a–e  77.41a–e  89.15a–d  7  89.20a  117.60ab  128.80ab  8  74.92abc  95.31a–d  107.6abc  9  39.50c–h  50.00cde  60.40bcd  10  54.70b–g  68.00b–e  77.50a–d  11  44.40b–h  64.70b–e  80.30a–d  12  39.70c–h  62.80b–e  72.20a–d  13  62.90a–d  93.10abc  114.30ab  14  31.58d–h  49.56cde  60.26bcd  15  32.90d–h  55.80cde  81.90a–d  16  28.20e–h  48.90cde  67.70bcd  17  76.2 ab  126.60a  135.50a  18  32.80d–h  56.90cde  80.10a–d  19  42.10c–h  74.00b–e  110.20ab  20  18.30h  32.10e  47.70cd  21  26.14e–h  52.90cde  76.94a–d  22  25.66fgh  47.80cde  65.10bcd  23  17.20h  29.97e  45.04cd  24  42.10b–h  82.70ad  103.40ab  25  33.40d–h  68.00b–e  88.90a–d  26  33.80d–h  61.30cde  80.20a–d  LSD  13.48–24.74  22.31–37.38  27.65–42.94  P  0.0001  0.0001  0.0001  Sorghum genotype*  Number of live weevils† per vial days after infestation of grain  63 d  84 d  105 d  1  23.70gh  32.80e  35.30d  2  37.20c–h  53.70cde  60.70bcd  3  49.30b–g  70.60be  90.40a–d  4  59.70a–f  80.40a–d  92.00a–d  5  30.20d–h  39.00de  38.50d  6  61.20a–e  77.41a–e  89.15a–d  7  89.20a  117.60ab  128.80ab  8  74.92abc  95.31a–d  107.6abc  9  39.50c–h  50.00cde  60.40bcd  10  54.70b–g  68.00b–e  77.50a–d  11  44.40b–h  64.70b–e  80.30a–d  12  39.70c–h  62.80b–e  72.20a–d  13  62.90a–d  93.10abc  114.30ab  14  31.58d–h  49.56cde  60.26bcd  15  32.90d–h  55.80cde  81.90a–d  16  28.20e–h  48.90cde  67.70bcd  17  76.2 ab  126.60a  135.50a  18  32.80d–h  56.90cde  80.10a–d  19  42.10c–h  74.00b–e  110.20ab  20  18.30h  32.10e  47.70cd  21  26.14e–h  52.90cde  76.94a–d  22  25.66fgh  47.80cde  65.10bcd  23  17.20h  29.97e  45.04cd  24  42.10b–h  82.70ad  103.40ab  25  33.40d–h  68.00b–e  88.90a–d  26  33.80d–h  61.30cde  80.20a–d  LSD  13.48–24.74  22.31–37.38  27.65–42.94  P  0.0001  0.0001  0.0001  Means followed by the same letter in a column are not significantly different (α = 0.05). Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. †Live weevils include all progeny and any still alive of the original five maize weevils per vial. View Large Table 2. Mean number of live maize weevils per vial at 63, 84, and 105 d after infestation Sorghum genotype*  Number of live weevils† per vial days after infestation of grain  63 d  84 d  105 d  1  23.70gh  32.80e  35.30d  2  37.20c–h  53.70cde  60.70bcd  3  49.30b–g  70.60be  90.40a–d  4  59.70a–f  80.40a–d  92.00a–d  5  30.20d–h  39.00de  38.50d  6  61.20a–e  77.41a–e  89.15a–d  7  89.20a  117.60ab  128.80ab  8  74.92abc  95.31a–d  107.6abc  9  39.50c–h  50.00cde  60.40bcd  10  54.70b–g  68.00b–e  77.50a–d  11  44.40b–h  64.70b–e  80.30a–d  12  39.70c–h  62.80b–e  72.20a–d  13  62.90a–d  93.10abc  114.30ab  14  31.58d–h  49.56cde  60.26bcd  15  32.90d–h  55.80cde  81.90a–d  16  28.20e–h  48.90cde  67.70bcd  17  76.2 ab  126.60a  135.50a  18  32.80d–h  56.90cde  80.10a–d  19  42.10c–h  74.00b–e  110.20ab  20  18.30h  32.10e  47.70cd  21  26.14e–h  52.90cde  76.94a–d  22  25.66fgh  47.80cde  65.10bcd  23  17.20h  29.97e  45.04cd  24  42.10b–h  82.70ad  103.40ab  25  33.40d–h  68.00b–e  88.90a–d  26  33.80d–h  61.30cde  80.20a–d  LSD  13.48–24.74  22.31–37.38  27.65–42.94  P  0.0001  0.0001  0.0001  Sorghum genotype*  Number of live weevils† per vial days after infestation of grain  63 d  84 d  105 d  1  23.70gh  32.80e  35.30d  2  37.20c–h  53.70cde  60.70bcd  3  49.30b–g  70.60be  90.40a–d  4  59.70a–f  80.40a–d  92.00a–d  5  30.20d–h  39.00de  38.50d  6  61.20a–e  77.41a–e  89.15a–d  7  89.20a  117.60ab  128.80ab  8  74.92abc  95.31a–d  107.6abc  9  39.50c–h  50.00cde  60.40bcd  10  54.70b–g  68.00b–e  77.50a–d  11  44.40b–h  64.70b–e  80.30a–d  12  39.70c–h  62.80b–e  72.20a–d  13  62.90a–d  93.10abc  114.30ab  14  31.58d–h  49.56cde  60.26bcd  15  32.90d–h  55.80cde  81.90a–d  16  28.20e–h  48.90cde  67.70bcd  17  76.2 ab  126.60a  135.50a  18  32.80d–h  56.90cde  80.10a–d  19  42.10c–h  74.00b–e  110.20ab  20  18.30h  32.10e  47.70cd  21  26.14e–h  52.90cde  76.94a–d  22  25.66fgh  47.80cde  65.10bcd  23  17.20h  29.97e  45.04cd  24  42.10b–h  82.70ad  103.40ab  25  33.40d–h  68.00b–e  88.90a–d  26  33.80d–h  61.30cde  80.20a–d  LSD  13.48–24.74  22.31–37.38  27.65–42.94  P  0.0001  0.0001  0.0001  Means followed by the same letter in a column are not significantly different (α = 0.05). Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. †Live weevils include all progeny and any still alive of the original five maize weevils per vial. View Large The cumulative total number of dead maize weevils from the initial population of five weevils per vial differed significantly at 63 (F = 1.85; df = 25, 226; P = 0.0105), 84 (F = 2.52; df = 25, 225; P = 0.0002), and 105 (F = 2.59; df = 25, 229; P = 0.0001) d after infestation. Of the original population of five weevils per vial, grain of (B35*B9501)-HD9 had highest number of dead weevils at 63 d after infestation (Table 3). At 84 and 105 d after infestation, grain of VG153*(TAM428*SBIII)-23 had the highest number of dead weevils. Fewest of the original maize weevils were dead in grain of (5BRON151*Tegemeo)-HG1 at 63 and 105 d of infestation and (A964*P850029)-HW6 at 84 d after infestation. Table 3. Mean cumulative number of dead maize weevils from the original population at 63, 84, and 105 d after infestation. Sorghum genotype*  Number of dead weevils/vial days after infestation of grain  63 d  84 d  105 d  1  2.30ab  2.60ab  3.40abc  2  1.40ab  1.40ab  2.40abc  3  2.00ab  2.10ab  2.70abc  4  2.00ab  2.10ab  2.40abc  5  3.30a  3.30a  4.10ab  6  1.90ab  2.04ab  2.62abc  7  1.40ab  1.50ab  2.40abc  8  1.67ab  2.00ab  3.11abc  9  1.70ab  3.40a  4.40a  10  2.20ab  2.30ab  3.20abc  11  0.90b  1.10b  2.10abc  12  1.20ab  1.40ab  2.80abc  13  1.10b  1.30ab  2.10bc  14  1.16b  1.43ab  2.45abc  15  1.50ab  1.60ab  2.20abc  16  1.60ab  1.70ab  2.90abc  17  0.91b  1.03b  1.87c  18  1.70ab  1.90ab  2.20abc  19  1.00b  1.20b  1.40c  20  2.10ab  2.40ab  2.70abc  21  1.79ab  1.99ab  3.20abc  22  1.57ab  1.70ab  1.98bc  23  2.01ab  2.45ab  2.68abc  24  1.20ab  1.30ab  1.80bc  25  1.60ab  1.70ab  3.30abc  26  1.60ab  1.80ab  2.90abc  LSD  0.96–1.28  0.97–1.30  1.05–1.45  P  0.0105  0.0002  0.0001  Sorghum genotype*  Number of dead weevils/vial days after infestation of grain  63 d  84 d  105 d  1  2.30ab  2.60ab  3.40abc  2  1.40ab  1.40ab  2.40abc  3  2.00ab  2.10ab  2.70abc  4  2.00ab  2.10ab  2.40abc  5  3.30a  3.30a  4.10ab  6  1.90ab  2.04ab  2.62abc  7  1.40ab  1.50ab  2.40abc  8  1.67ab  2.00ab  3.11abc  9  1.70ab  3.40a  4.40a  10  2.20ab  2.30ab  3.20abc  11  0.90b  1.10b  2.10abc  12  1.20ab  1.40ab  2.80abc  13  1.10b  1.30ab  2.10bc  14  1.16b  1.43ab  2.45abc  15  1.50ab  1.60ab  2.20abc  16  1.60ab  1.70ab  2.90abc  17  0.91b  1.03b  1.87c  18  1.70ab  1.90ab  2.20abc  19  1.00b  1.20b  1.40c  20  2.10ab  2.40ab  2.70abc  21  1.79ab  1.99ab  3.20abc  22  1.57ab  1.70ab  1.98bc  23  2.01ab  2.45ab  2.68abc  24  1.20ab  1.30ab  1.80bc  25  1.60ab  1.70ab  3.30abc  26  1.60ab  1.80ab  2.90abc  LSD  0.96–1.28  0.97–1.30  1.05–1.45  P  0.0105  0.0002  0.0001  Means followed by the same letter in a column are not significantly different (α = 0.05). Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. View Large Table 3. Mean cumulative number of dead maize weevils from the original population at 63, 84, and 105 d after infestation. Sorghum genotype*  Number of dead weevils/vial days after infestation of grain  63 d  84 d  105 d  1  2.30ab  2.60ab  3.40abc  2  1.40ab  1.40ab  2.40abc  3  2.00ab  2.10ab  2.70abc  4  2.00ab  2.10ab  2.40abc  5  3.30a  3.30a  4.10ab  6  1.90ab  2.04ab  2.62abc  7  1.40ab  1.50ab  2.40abc  8  1.67ab  2.00ab  3.11abc  9  1.70ab  3.40a  4.40a  10  2.20ab  2.30ab  3.20abc  11  0.90b  1.10b  2.10abc  12  1.20ab  1.40ab  2.80abc  13  1.10b  1.30ab  2.10bc  14  1.16b  1.43ab  2.45abc  15  1.50ab  1.60ab  2.20abc  16  1.60ab  1.70ab  2.90abc  17  0.91b  1.03b  1.87c  18  1.70ab  1.90ab  2.20abc  19  1.00b  1.20b  1.40c  20  2.10ab  2.40ab  2.70abc  21  1.79ab  1.99ab  3.20abc  22  1.57ab  1.70ab  1.98bc  23  2.01ab  2.45ab  2.68abc  24  1.20ab  1.30ab  1.80bc  25  1.60ab  1.70ab  3.30abc  26  1.60ab  1.80ab  2.90abc  LSD  0.96–1.28  0.97–1.30  1.05–1.45  P  0.0105  0.0002  0.0001  Sorghum genotype*  Number of dead weevils/vial days after infestation of grain  63 d  84 d  105 d  1  2.30ab  2.60ab  3.40abc  2  1.40ab  1.40ab  2.40abc  3  2.00ab  2.10ab  2.70abc  4  2.00ab  2.10ab  2.40abc  5  3.30a  3.30a  4.10ab  6  1.90ab  2.04ab  2.62abc  7  1.40ab  1.50ab  2.40abc  8  1.67ab  2.00ab  3.11abc  9  1.70ab  3.40a  4.40a  10  2.20ab  2.30ab  3.20abc  11  0.90b  1.10b  2.10abc  12  1.20ab  1.40ab  2.80abc  13  1.10b  1.30ab  2.10bc  14  1.16b  1.43ab  2.45abc  15  1.50ab  1.60ab  2.20abc  16  1.60ab  1.70ab  2.90abc  17  0.91b  1.03b  1.87c  18  1.70ab  1.90ab  2.20abc  19  1.00b  1.20b  1.40c  20  2.10ab  2.40ab  2.70abc  21  1.79ab  1.99ab  3.20abc  22  1.57ab  1.70ab  1.98bc  23  2.01ab  2.45ab  2.68abc  24  1.20ab  1.30ab  1.80bc  25  1.60ab  1.70ab  3.30abc  26  1.60ab  1.80ab  2.90abc  LSD  0.96–1.28  0.97–1.30  1.05–1.45  P  0.0105  0.0002  0.0001  Means followed by the same letter in a column are not significantly different (α = 0.05). Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. View Large Damage Score The mean damage score of the 26 sorghum genotypes at 21 (F = 23.11; df = 25, 229; P = 0.0001), 42 (F = 10.43; df = 25, 229; P = 0.0001), 63 (F = 8.73; df = 25, 229; P = 0.0001), 84 (F = 6.92; df = 25, 229; P = 0.0001), and 105 (F = 8.21; df = 25, 229; P = 0.0001) d after infestation with maize weevils differed significantly. Sorghum genotypes Sureo, (SV1*Sima/IS23250)-LG15, (5BRON151*Tegemeo)-HG7, and (B35*B9501)-HD9 ranked among the top four genotypes with least damage rating more often than any other genotypes across the five sampling dates (Table 4). On the other hand, genotypes B.HF8, (A964*P850029)-HW6, (Segaolane*WM#322)-LG2, and (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1 were more often ranked among the top four genotypes with highest damage rating across the sampling dates compared to other genotypes. Table 4. Mean damage score across sorghum genotypes Sorghum genotype*  Mean damage score† days after infestation of grain  21 d  42 d  63 d  84 d  105 d  1  1.04k  1.15g  1.62fgh  1.80fg  1.88h  2  1.07jk  1.25c–g  1.89c–h  2.29c–g  2.60c–h  3  1.15d–i  1.38b–e  2.15b–f  2.71b–e  3.30b–e  4  1.09h–k  1.25d–g  2.18b–f  2.60b–f  3.32b–f  5  1.08ijk  1.18fg  1.72fgh  1.84fg  2.19e–h  6  1.09g–k  1.31b–f  2.28b–e  2.63b–f  3.29b–f  7  1.12e–j  1.42b  2.95a  3.51a  4.47a  8  1.11f–j  1.35b–e  2.43bc  3.12abc  3.79a–d  9  1.10f–k  1.32b–f  1.93c–h  2.17d–g  2.62c–h  10  1.10f–k  1.29b–g  2.02b–h  2.43c–g  3.00c–g  11  1.15d–j  1.41bc  2.08b–g  2.44c–g  3.18b–g  12  1.12f–j  1.28b–g  1.85d–h  2.18d–g  2.77c–h  13  1.18c–f  1.39bcd  2.33bcd  2.82a–e  4.21ab  14  1.15d–j  1.29b–g  1.84d–h  2.15d–g  2.56c–h  15  1.17c–h  1.38b–e  1.98c–h  2.34c–g  3.16b–g  16  1.13e–j  1.33b–f  1.76e–h  1.99efg  2.49d–h  17  1.20cde  1.42b  2.40bc  3.28ab  4.63a  18  1.11f–j  1.23efg  1.67fgh  2.18d–g  2.80c–h  19  1.17c–g  1.32b–f  1.98c–h  2.38c–g  3.58a–d  20  1.13e–j  1.24d–g  1.54h  1.73g  2.13fgh  21  1.23c  1.37b–e  1.77e–h  2.12d–g  2.56c–h  22  1.23c  1.34b–e  1.81d–h  2.09d–g  2.73c–h  23  1.15d–j  1.23efg  1.58gh  1.74g  2.08gh  24  1.44a  1.69a  2.51b  2.90a–d  3.75abc  25  1.30b  1.36b–e  1.86d–h  2.45c–g  3.13b–g  26  1.22cd  1.30b–f  1.82d–h  2.33c–g  3.08b–g  LSD  0.05  0.08–0.09  0.28–0.34  0.43–0.53  0.59–0.79  P  0.0001  0.0001  0.0001  0.0001  0.0001  Sorghum genotype*  Mean damage score† days after infestation of grain  21 d  42 d  63 d  84 d  105 d  1  1.04k  1.15g  1.62fgh  1.80fg  1.88h  2  1.07jk  1.25c–g  1.89c–h  2.29c–g  2.60c–h  3  1.15d–i  1.38b–e  2.15b–f  2.71b–e  3.30b–e  4  1.09h–k  1.25d–g  2.18b–f  2.60b–f  3.32b–f  5  1.08ijk  1.18fg  1.72fgh  1.84fg  2.19e–h  6  1.09g–k  1.31b–f  2.28b–e  2.63b–f  3.29b–f  7  1.12e–j  1.42b  2.95a  3.51a  4.47a  8  1.11f–j  1.35b–e  2.43bc  3.12abc  3.79a–d  9  1.10f–k  1.32b–f  1.93c–h  2.17d–g  2.62c–h  10  1.10f–k  1.29b–g  2.02b–h  2.43c–g  3.00c–g  11  1.15d–j  1.41bc  2.08b–g  2.44c–g  3.18b–g  12  1.12f–j  1.28b–g  1.85d–h  2.18d–g  2.77c–h  13  1.18c–f  1.39bcd  2.33bcd  2.82a–e  4.21ab  14  1.15d–j  1.29b–g  1.84d–h  2.15d–g  2.56c–h  15  1.17c–h  1.38b–e  1.98c–h  2.34c–g  3.16b–g  16  1.13e–j  1.33b–f  1.76e–h  1.99efg  2.49d–h  17  1.20cde  1.42b  2.40bc  3.28ab  4.63a  18  1.11f–j  1.23efg  1.67fgh  2.18d–g  2.80c–h  19  1.17c–g  1.32b–f  1.98c–h  2.38c–g  3.58a–d  20  1.13e–j  1.24d–g  1.54h  1.73g  2.13fgh  21  1.23c  1.37b–e  1.77e–h  2.12d–g  2.56c–h  22  1.23c  1.34b–e  1.81d–h  2.09d–g  2.73c–h  23  1.15d–j  1.23efg  1.58gh  1.74g  2.08gh  24  1.44a  1.69a  2.51b  2.90a–d  3.75abc  25  1.30b  1.36b–e  1.86d–h  2.45c–g  3.13b–g  26  1.22cd  1.30b–f  1.82d–h  2.33c–g  3.08b–g  LSD  0.05  0.08–0.09  0.28–0.34  0.43–0.53  0.59–0.79  P  0.0001  0.0001  0.0001  0.0001  0.0001  Means followed by the same letter in a column are not significantly different. Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. †Damage was scored on a scale of 1–5, where 1 = no evidence of feeding; 2 = some feeding at surface such as one feeding hole but not all the way through the grain (involving 1–25% of the grain); 3 = two tunnels through the grain (26–50% damaged); 4 = more than two holes and/or grain was 51–75% damaged; 5 = many feeding tunnels in grain (76–100% damaged). View Large Table 4. Mean damage score across sorghum genotypes Sorghum genotype*  Mean damage score† days after infestation of grain  21 d  42 d  63 d  84 d  105 d  1  1.04k  1.15g  1.62fgh  1.80fg  1.88h  2  1.07jk  1.25c–g  1.89c–h  2.29c–g  2.60c–h  3  1.15d–i  1.38b–e  2.15b–f  2.71b–e  3.30b–e  4  1.09h–k  1.25d–g  2.18b–f  2.60b–f  3.32b–f  5  1.08ijk  1.18fg  1.72fgh  1.84fg  2.19e–h  6  1.09g–k  1.31b–f  2.28b–e  2.63b–f  3.29b–f  7  1.12e–j  1.42b  2.95a  3.51a  4.47a  8  1.11f–j  1.35b–e  2.43bc  3.12abc  3.79a–d  9  1.10f–k  1.32b–f  1.93c–h  2.17d–g  2.62c–h  10  1.10f–k  1.29b–g  2.02b–h  2.43c–g  3.00c–g  11  1.15d–j  1.41bc  2.08b–g  2.44c–g  3.18b–g  12  1.12f–j  1.28b–g  1.85d–h  2.18d–g  2.77c–h  13  1.18c–f  1.39bcd  2.33bcd  2.82a–e  4.21ab  14  1.15d–j  1.29b–g  1.84d–h  2.15d–g  2.56c–h  15  1.17c–h  1.38b–e  1.98c–h  2.34c–g  3.16b–g  16  1.13e–j  1.33b–f  1.76e–h  1.99efg  2.49d–h  17  1.20cde  1.42b  2.40bc  3.28ab  4.63a  18  1.11f–j  1.23efg  1.67fgh  2.18d–g  2.80c–h  19  1.17c–g  1.32b–f  1.98c–h  2.38c–g  3.58a–d  20  1.13e–j  1.24d–g  1.54h  1.73g  2.13fgh  21  1.23c  1.37b–e  1.77e–h  2.12d–g  2.56c–h  22  1.23c  1.34b–e  1.81d–h  2.09d–g  2.73c–h  23  1.15d–j  1.23efg  1.58gh  1.74g  2.08gh  24  1.44a  1.69a  2.51b  2.90a–d  3.75abc  25  1.30b  1.36b–e  1.86d–h  2.45c–g  3.13b–g  26  1.22cd  1.30b–f  1.82d–h  2.33c–g  3.08b–g  LSD  0.05  0.08–0.09  0.28–0.34  0.43–0.53  0.59–0.79  P  0.0001  0.0001  0.0001  0.0001  0.0001  Sorghum genotype*  Mean damage score† days after infestation of grain  21 d  42 d  63 d  84 d  105 d  1  1.04k  1.15g  1.62fgh  1.80fg  1.88h  2  1.07jk  1.25c–g  1.89c–h  2.29c–g  2.60c–h  3  1.15d–i  1.38b–e  2.15b–f  2.71b–e  3.30b–e  4  1.09h–k  1.25d–g  2.18b–f  2.60b–f  3.32b–f  5  1.08ijk  1.18fg  1.72fgh  1.84fg  2.19e–h  6  1.09g–k  1.31b–f  2.28b–e  2.63b–f  3.29b–f  7  1.12e–j  1.42b  2.95a  3.51a  4.47a  8  1.11f–j  1.35b–e  2.43bc  3.12abc  3.79a–d  9  1.10f–k  1.32b–f  1.93c–h  2.17d–g  2.62c–h  10  1.10f–k  1.29b–g  2.02b–h  2.43c–g  3.00c–g  11  1.15d–j  1.41bc  2.08b–g  2.44c–g  3.18b–g  12  1.12f–j  1.28b–g  1.85d–h  2.18d–g  2.77c–h  13  1.18c–f  1.39bcd  2.33bcd  2.82a–e  4.21ab  14  1.15d–j  1.29b–g  1.84d–h  2.15d–g  2.56c–h  15  1.17c–h  1.38b–e  1.98c–h  2.34c–g  3.16b–g  16  1.13e–j  1.33b–f  1.76e–h  1.99efg  2.49d–h  17  1.20cde  1.42b  2.40bc  3.28ab  4.63a  18  1.11f–j  1.23efg  1.67fgh  2.18d–g  2.80c–h  19  1.17c–g  1.32b–f  1.98c–h  2.38c–g  3.58a–d  20  1.13e–j  1.24d–g  1.54h  1.73g  2.13fgh  21  1.23c  1.37b–e  1.77e–h  2.12d–g  2.56c–h  22  1.23c  1.34b–e  1.81d–h  2.09d–g  2.73c–h  23  1.15d–j  1.23efg  1.58gh  1.74g  2.08gh  24  1.44a  1.69a  2.51b  2.90a–d  3.75abc  25  1.30b  1.36b–e  1.86d–h  2.45c–g  3.13b–g  26  1.22cd  1.30b–f  1.82d–h  2.33c–g  3.08b–g  LSD  0.05  0.08–0.09  0.28–0.34  0.43–0.53  0.59–0.79  P  0.0001  0.0001  0.0001  0.0001  0.0001  Means followed by the same letter in a column are not significantly different. Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. †Damage was scored on a scale of 1–5, where 1 = no evidence of feeding; 2 = some feeding at surface such as one feeding hole but not all the way through the grain (involving 1–25% of the grain); 3 = two tunnels through the grain (26–50% damaged); 4 = more than two holes and/or grain was 51–75% damaged; 5 = many feeding tunnels in grain (76–100% damaged). View Large Weight Loss Weight of the sorghum grain differed significantly among the 26 genotypes at 105 (F = 3.81; df = 25, 229; P = 0.0001) d after infestation with maize weevils (Fig. 1). The least percentages of weight loss of 23.88 and 24.11% were recorded for sorghum genotypes Sureño and (5BRON151*Tegemeo)-HG7, respectively. Genotypes B.HF8 and (A964*P850029)-HW6 had lost most weight, 70.62 and 67.69%, at 105 d after infestation by maize weevils. There was no strong relationship between kernel weight and number of live weevils (R2 = 0.02, P = 0.0223). Also, no significant relationship was found between kernel weight and damage score (R2 = 0.01, P = 0.1105), and kernel weight and grain weight loss (R2 = 0.0029, P = 0.3929). Discussion Sorghum genotypes used in the study showed a wide range of resistance and susceptibility to maize weevil. Genotypes Sureño, (5BRON151*Tegemeo)-HG7, (SV1*Sima/IS23250)-LG15, and (B35*B9501)-HD9 were the most resistant to maize weevils as they had least number of live weevils, damage score, and grain weight loss. On the other hand, number of live weevils, damage score, and weight loss were highest in genotypes B.HF8, (A964*P850029)-HW6, (9MLT176*A964)-LG8, and (Segaolane*WM#322)-LG2 indicating their susceptibility to maize weevil. These genotypes favored survival and emergence of large number of maize weevils throughout the experimental period. All remaining sorghum genotypes exhibited intermediate levels of resistance against maize weevil. Our results agree with that of Chitio (2004) study that showed resistance of Sureño grain to maize weevil (Chitio et al. 2004). Genotypes evaluated in the current study are primarily developed for improved agronomic reasons such as drought tolerance, resistance to insect pests in field, and improved grain quality. Significant variability in level of resistance to maize weevil among these genotypes set a stage for follow-up studies to investigate mechanisms of postharvest resistance to stored grain pests. Use of resistant sorghum genotypes can be an effective strategy to reduce food grain losses especially in the developing world where substantial food grain losses occur to storage insect pests due to inadequate storage facilities. Initial steps in development of insect-resistant cultivars include the identification of resistant sources and the mechanisms of resistance. Plants exhibit resistance to insect pests through different mechanisms, which includes antibiosis (the plant affects insect pest biology adversely), antixenosis (the plant is not a preferred host), and tolerance (the plant has the ability to withstand or recover from insect damage and produces normal yield) (Smith 1989). In the current study, we evaluated sorghum genotypes for resistance to maize weevil by determining weevil survival and mortality, damage rating, and grain weight loss by artificially infesting grain of each genotype with maize weevils under laboratory conditions. However, little emphasis was given toward investigating the mechanisms of resistance to maize weevil. Therefore, future studies should be conducted to elucidate mechanisms(s) of resistance in sorghum genotypes to maize weevil. Chemical composition of seed can be studied to determine whether antibiotic activity (antibiosis) exists in resistant genotypes such as Sureño. Several studies have shown that certain chemical composition and/or physical properties of grain could make it favorable or less favorable to survival and reproduction of maize weevil (Russell 1962, Doraiswamy 1976, Adetunji 1988, Reddy 2002). Adetunji (1988) found sorghum grain resistance to Sitophilus oryzae (L.) to be associated with greater larval mortality, longer developmental periods (antibiosis), and reduced oviposition (nonpreference). Phenolic acids have been studied extensively as biochemical components correlated with maize weevil resistance in maize (Arnason et al. 1997). Also, susceptibility to maize weevil has been related to nutritional quality traits such as sugar, protein, fat, and amino acids in maize (Dobie 1977, Classen et al. 1990). Physical factors such as grain hardness and pericarp surface texture can also impart resistance or susceptibility to maize weevil (Doraiswamy 1976, Dobie 1977, García-Lara et al. 2004). Seed size has been reported to influence the level of resistance and susceptibility to stored-grain pests (Mills 1985, Wongo 1990). In the current study, however, no correlation between kernel weight and the level of resistance to maize weevil was found. Pendleton et al. (2011) examined maize weevil resistant sorghum genotypes using a scanning electronic microscope and demonstrated a positive correlation between the depth of a band of concentrated iodine (with bound starch) measured from the seed coat and the degree of resistance to damage by the maize weevil (Pendleton et al. 2011, 2012). Similar investigations can be done on the sorghum genotypes studied in the current study to determine whether correlation exists between any of the physical or chemical properties of grain and the resistance to the maize weevil. Despite the substantial sorghum grain losses to stored-grain pests such as maize weevil, little emphasis has been given toward developing commercial cultivars with postharvest resistance to stored-grain insect pests. Under the circumstances, studies on identifying resistant sources and understanding mechanisms of resistance will help developing commercial sorghum cultivars resistant to stored-grain insect pests through traditional and molecular breeding techniques. To summarize, this study provides information on the level of resistance among selected sorghum genotypes to maize weevil. Research to identify maize weevil–resistant germplasm and traits associated with resistance needs to be continued to facilitate development of maize weevil–resistant sorghum. Development of commercial sorghum cultivars resistant to maize weevil will help reduce grain losses especially in developing countries where storage structures and resources to manage stored-grain pests are scarce. Fig. 1. View largeDownload slide Percentage of weight loss of sorghum grain at 105 d after infestation with maize weevils (weight without weevils). Bars showing same letter are not significantly different (α = 0.05). The figure is based on untransformed data while statistics were generated on square root of (X + 0.5) transformed data. See Table 1 for genotype pedigree. Fig. 1. View largeDownload slide Percentage of weight loss of sorghum grain at 105 d after infestation with maize weevils (weight without weevils). Bars showing same letter are not significantly different (α = 0.05). The figure is based on untransformed data while statistics were generated on square root of (X + 0.5) transformed data. See Table 1 for genotype pedigree. Acknowledgments This work was financially supported in part by the International Sorghum, Millet and Other Grains Collaborative Research Support Program (INTSORMIL CRSP). References Cited Adetunji, J. F. 1988. 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Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Environmental Entomology Oxford University Press

Resistance of Selected Sorghum Genotypes to Maize Weevil (Coleoptera: Curculionidae)

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Entomological Society of America
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© The Author(s) 2018. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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0046-225X
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1938-2936
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10.1093/ee/nvy049
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Abstract

Abstract The maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), is a major insect pest of stored grain. This study evaluated resistance of grain of 26 sorghum genotypes, Sorghum bicolor (L.) Moench, to maize weevil under laboratory conditions. Three female and two male newly emerged maize weevils were reared with 5 g of grain in each of 10 vials for each of the 26 sorghum genotypes in a laboratory experiment. The weevils and grain of each genotype were scored once every 3 wk for a total of five times during 105 d. The numbers of live and newly emerged maize weevils, dead weevils from the initial population, damage score (scale of 1–5), and grain weight loss were used to indicate resistance. The least percentage weight loss of 23.9 and 24.1% was recorded for sorghum genotypes Sureño and (5BRON151*Tegemeo)-HG7, respectively. Genotypes B.HF8 and (A964*P850029)-HW6 had the most weight loss, 70.6 and 67.7%, at 105 d after infestation. Genotypes B.HF8 and (A964*P850029)-HW6 consistently exhibited the highest numbers of maize weevil, 63 and 84, per vial at 105 d after infestation. Sorghum genotypes Sureño, (SV1*Sima/IS23250)-LG15, (5BRON151*Tegemeo)-HG7, and (B35*B9501)-HD9 ranked among the top four genotypes with least damage rating more often than any other genotype across the five sampling dates. On the other hand, genotypes B.HF8, (A964*P850029)-HW6, (Segaolane*WM#322)LG2, and (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1 were more often ranked among the top four genotypes with the highest damage rating. Our results indicate that grain of genotype Sureno is most resistant to the maize weevil among screened genotypes. Sitophilus, zeamais, Sorghum, bicolor, resistance The maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), is one of the most destructive and widely distributed primary insect pests of stored grain (Teetes et al. 1981, Throne 1994). It is primarily associated with maize, Zea mays L., but can develop on all cereal grains and cereal products (Walgenbach and Burkholder 1986, Tipping et al. 1987). Hosts of maize weevil include barley, Hordeum vulgare L., maize, oats, Avena sativa L., sorghum, Sorghum bicolor L. and wheat, Triticum sp. L. (Morrison 1963). The common sources of stored grain pests are grain spills, old grain, seed, feeds, and grain debris. Insects often move from carryover grain, uncleaned empty bins, feed supply buildings, and grain debris beneath perforated bin floors into grain newly put into storage. Maize weevil can also infest developing kernels in the field (Caswell 1961, Vyavhare 2010, Vyavhare and Pendleton 2011) and are taken into storage where they continue to live and damage stored grain. The adult maize weevil lives an average of 2 to 5 mo, and each female lays about 300 to 400 eggs during this period (Morrison 1963). The female chews small cavities into kernels and lays eggs individually. She seals the cavities with a sticky secretion from her anus. Eggs hatch in 6 d and the larvae feed inside the grain. After passing through four instars, the larvae pupate inside the grain. The life cycle averages 39 d under optimal conditions (Morrison 1963, Wilbur and Mills 1985). Adults and larvae feed on grain, with major damage by larvae developing inside kernels. Because the insects feed inside grain, they and their excreta are ground along with grain during milling. Infestation by maize weevils reduces the quality and viability of seed and seedling vigor. Fungi grow on the insect exuvia and excreta. The presence of insects also reduces the commercial value of the grain. Worldwide sorghum grain losses to maize weevil and other stored grain pests can range from 15 to 77% (Nyambo 1993, Ramputh et al. 1999, Goftishu and Belete 2014). Grain losses to maize weevil are more pronounced in the tropical and subtropical agroecosystems where environmental factors are conducive for the reproduction and development of weevils, and where storage facilities are inadequate (Tigar et al. 1994, Goftishu and Belete 2014). Many practices are used to protect grain from storage insects. Cultural management practices include sanitation, drying, cleaning, and aeration (Allotey 1991). Cultural practices help to reduce grain losses only to a certain extent because internal infestation and contamination cannot all be removed by ordinary cultural practices such as cleaning. Synthetic insecticides are one of the widely used control measures against storage pests, but the use of persistent and wide-spectrum organochlorine and some organophosphate compounds has led to health and environmental concerns (Markowitz 1992). In addition, use of synthetic insecticides poses high risk of development of resistance in insect populations and nontarget effects (Zettler and Cuperus 1990, Bekele et al. 1997). For instance, a global survey of susceptibility of stored grain pests to insecticides showed widespread resistance by major stored grain insect pests to malathion and lindane (Champ and Dyte 1976). This necessitates searching for alternative management tactics that are effective, economical, and environment friendly. Insect-resistant cultivars are an important component of integrated pest management. The use of resistant or less susceptible cultivars integrated with other sustainable pest control methods can provide a longer lasting solution to losses in storage (Dobie 1977). Resistance of sorghum to various insect pests in the field has been studied by many researchers (Agrawal et al. 1990, Nwanze et al. 1991), but resistance to stored-grain pests has been one of the neglected areas of sorghum entomology. The current study was conducted with the objective to evaluate resistance of 26 genotypes of sorghum to maize weevil under laboratory conditions. Materials and Methods The grain of 26 genotypes of sorghum was evaluated for resistance to maize weevil under laboratory conditions at West Texas A&M University, Canyon, TX. Table 1 lists the 26 genotypes used in the experiment. The grain of all genotypes was obtained from the Sorghum Improvement Program at the Texas A&M AgriLife Research and Extension Center in Lubbock, TX. Table 1. List of sorghum genotypes evaluated for resistance to maize weevil No.  Pedigree  Reasoning  1  Sureño  Line developed and released for improved grain quality and resistance to grain mold/weathering  2  Macia  Introduction from Southern Africa with improved grain quality  3  CE151  Introduction from Senegal with preflowering drought tolerance and resistance to sugarcane aphid  4  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864 *PI550607)))))-PR3-CM3  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  5  (B35*B9501)-HD9  Germplasm developed with resistance to postflowering drought stress  6  B409  Germplasm developed with resistance to postflowering drought stress  7  B.HF8  Germplasm developed with resistance to postflowering drought stress  8  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  9  VG153*(TAM428*SBIII)-23  Germplasm developed for improved grain quality  10  (85OG4300-5*Tx2782)-SM5  Germplasm developed for resistance to sorghum midge  11  (M84-7*VG153)-LBK  Germplasm developed for improved grain quality  12  (9MLT176*A964)-CA3  Germplasm developed for resistance to sorghum midge  13  (9MLT176*A964)-LG8  Germplasm developed for resistance to sorghum midge  14  (Dorado*Tegemeo)-HW13  Germplasm developed for improved grain quality  15  (Dorado*Tegemeo)-HW14  Germplasm developed for improved grain quality  16  (Dorado*Tegemeo)-HW15  Germplasm developed for improved grain quality  17  (A964*P850029)-HW6  Germplasm developed for improved adaptation  18  Tegemeo  Introduction from Southern Africa with improved grain quality and adaptation  19  (5BRON151*Tegemeo)-HG1  Germplasm developed for improved grain quality  20  (5BRON151*Tegemeo)-HG7  Germplasm developed for improved grain quality  21  (Kuyuma*5BRON155)-CA5  Germplasm developed for improved grain quality  22  (Macia*TAM428)-LL9  Germplasm developed for resistance to sugarcane aphid in South Africa  23  (SV1*Sima/IS23250)-LG15  Germplasm developed for resistance to sugarcane aphid in South Africa  24  (Segaolane*WM#322)-LG2  Germplasm developed for resistance to sugarcane aphid in South Africa  25  (6BRON161*CE151)-LG5  Germplasm developed for resistance to sugarcane aphid in South Africa  26  (Macia*TAM428)-LL2  Germplasm developed for resistance to sugarcane aphid in South Africa  No.  Pedigree  Reasoning  1  Sureño  Line developed and released for improved grain quality and resistance to grain mold/weathering  2  Macia  Introduction from Southern Africa with improved grain quality  3  CE151  Introduction from Senegal with preflowering drought tolerance and resistance to sugarcane aphid  4  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864 *PI550607)))))-PR3-CM3  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  5  (B35*B9501)-HD9  Germplasm developed with resistance to postflowering drought stress  6  B409  Germplasm developed with resistance to postflowering drought stress  7  B.HF8  Germplasm developed with resistance to postflowering drought stress  8  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  9  VG153*(TAM428*SBIII)-23  Germplasm developed for improved grain quality  10  (85OG4300-5*Tx2782)-SM5  Germplasm developed for resistance to sorghum midge  11  (M84-7*VG153)-LBK  Germplasm developed for improved grain quality  12  (9MLT176*A964)-CA3  Germplasm developed for resistance to sorghum midge  13  (9MLT176*A964)-LG8  Germplasm developed for resistance to sorghum midge  14  (Dorado*Tegemeo)-HW13  Germplasm developed for improved grain quality  15  (Dorado*Tegemeo)-HW14  Germplasm developed for improved grain quality  16  (Dorado*Tegemeo)-HW15  Germplasm developed for improved grain quality  17  (A964*P850029)-HW6  Germplasm developed for improved adaptation  18  Tegemeo  Introduction from Southern Africa with improved grain quality and adaptation  19  (5BRON151*Tegemeo)-HG1  Germplasm developed for improved grain quality  20  (5BRON151*Tegemeo)-HG7  Germplasm developed for improved grain quality  21  (Kuyuma*5BRON155)-CA5  Germplasm developed for improved grain quality  22  (Macia*TAM428)-LL9  Germplasm developed for resistance to sugarcane aphid in South Africa  23  (SV1*Sima/IS23250)-LG15  Germplasm developed for resistance to sugarcane aphid in South Africa  24  (Segaolane*WM#322)-LG2  Germplasm developed for resistance to sugarcane aphid in South Africa  25  (6BRON161*CE151)-LG5  Germplasm developed for resistance to sugarcane aphid in South Africa  26  (Macia*TAM428)-LL2  Germplasm developed for resistance to sugarcane aphid in South Africa  View Large Table 1. List of sorghum genotypes evaluated for resistance to maize weevil No.  Pedigree  Reasoning  1  Sureño  Line developed and released for improved grain quality and resistance to grain mold/weathering  2  Macia  Introduction from Southern Africa with improved grain quality  3  CE151  Introduction from Senegal with preflowering drought tolerance and resistance to sugarcane aphid  4  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864 *PI550607)))))-PR3-CM3  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  5  (B35*B9501)-HD9  Germplasm developed with resistance to postflowering drought stress  6  B409  Germplasm developed with resistance to postflowering drought stress  7  B.HF8  Germplasm developed with resistance to postflowering drought stress  8  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  9  VG153*(TAM428*SBIII)-23  Germplasm developed for improved grain quality  10  (85OG4300-5*Tx2782)-SM5  Germplasm developed for resistance to sorghum midge  11  (M84-7*VG153)-LBK  Germplasm developed for improved grain quality  12  (9MLT176*A964)-CA3  Germplasm developed for resistance to sorghum midge  13  (9MLT176*A964)-LG8  Germplasm developed for resistance to sorghum midge  14  (Dorado*Tegemeo)-HW13  Germplasm developed for improved grain quality  15  (Dorado*Tegemeo)-HW14  Germplasm developed for improved grain quality  16  (Dorado*Tegemeo)-HW15  Germplasm developed for improved grain quality  17  (A964*P850029)-HW6  Germplasm developed for improved adaptation  18  Tegemeo  Introduction from Southern Africa with improved grain quality and adaptation  19  (5BRON151*Tegemeo)-HG1  Germplasm developed for improved grain quality  20  (5BRON151*Tegemeo)-HG7  Germplasm developed for improved grain quality  21  (Kuyuma*5BRON155)-CA5  Germplasm developed for improved grain quality  22  (Macia*TAM428)-LL9  Germplasm developed for resistance to sugarcane aphid in South Africa  23  (SV1*Sima/IS23250)-LG15  Germplasm developed for resistance to sugarcane aphid in South Africa  24  (Segaolane*WM#322)-LG2  Germplasm developed for resistance to sugarcane aphid in South Africa  25  (6BRON161*CE151)-LG5  Germplasm developed for resistance to sugarcane aphid in South Africa  26  (Macia*TAM428)-LL2  Germplasm developed for resistance to sugarcane aphid in South Africa  No.  Pedigree  Reasoning  1  Sureño  Line developed and released for improved grain quality and resistance to grain mold/weathering  2  Macia  Introduction from Southern Africa with improved grain quality  3  CE151  Introduction from Senegal with preflowering drought tolerance and resistance to sugarcane aphid  4  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864 *PI550607)))))-PR3-CM3  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  5  (B35*B9501)-HD9  Germplasm developed with resistance to postflowering drought stress  6  B409  Germplasm developed with resistance to postflowering drought stress  7  B.HF8  Germplasm developed with resistance to postflowering drought stress  8  (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1  Germplasm developed for resistance to sorghum midge and greenbug biotypes E and I  9  VG153*(TAM428*SBIII)-23  Germplasm developed for improved grain quality  10  (85OG4300-5*Tx2782)-SM5  Germplasm developed for resistance to sorghum midge  11  (M84-7*VG153)-LBK  Germplasm developed for improved grain quality  12  (9MLT176*A964)-CA3  Germplasm developed for resistance to sorghum midge  13  (9MLT176*A964)-LG8  Germplasm developed for resistance to sorghum midge  14  (Dorado*Tegemeo)-HW13  Germplasm developed for improved grain quality  15  (Dorado*Tegemeo)-HW14  Germplasm developed for improved grain quality  16  (Dorado*Tegemeo)-HW15  Germplasm developed for improved grain quality  17  (A964*P850029)-HW6  Germplasm developed for improved adaptation  18  Tegemeo  Introduction from Southern Africa with improved grain quality and adaptation  19  (5BRON151*Tegemeo)-HG1  Germplasm developed for improved grain quality  20  (5BRON151*Tegemeo)-HG7  Germplasm developed for improved grain quality  21  (Kuyuma*5BRON155)-CA5  Germplasm developed for improved grain quality  22  (Macia*TAM428)-LL9  Germplasm developed for resistance to sugarcane aphid in South Africa  23  (SV1*Sima/IS23250)-LG15  Germplasm developed for resistance to sugarcane aphid in South Africa  24  (Segaolane*WM#322)-LG2  Germplasm developed for resistance to sugarcane aphid in South Africa  25  (6BRON161*CE151)-LG5  Germplasm developed for resistance to sugarcane aphid in South Africa  26  (Macia*TAM428)-LL2  Germplasm developed for resistance to sugarcane aphid in South Africa  View Large Maize weevils were cultured on popcorn seeds in 0.95-liter glass jars in the laboratory. To ensure enough newly emerged maize weevils to infest grain of the genotypes, six jars were maintained with popcorn and live maize weevils. The top of each jar was covered by a piece of organdy cloth under the metal jar ring screwed onto the top. The jars of maize weevils were maintained at 25–27°C and 70% relative humidity. Popcorn was added to each jar regularly to ensure enough food for the maize weevil colony. Prior to the beginning of experiment, grain of all genotypes was kept at room temperature (25–27°C) and relative humidity of 65–70% for 10 d to bring the equilibrium moisture content of grain to ~14%. Weight of individual sorghum kernels was measured to relate it to damage caused by maize weevils. One gram of grain of each of sorghum genotype was weighed, and the number of grains per gram was counted. Five replications were used of each of the genotypes to count the number of kernels per gram. The weight of 100 kernels was determined for each sorghum genotype. Between 6 June and 21 November 2009, grains of 26 genotypes of sorghum (Table 1) were evaluated for resistance to maize weevil. Ten plastic 20-ml scintillation vials were used for each genotype of sorghum. Three female and two male maize weevils that emerged that day from a colony maintained on popcorn were placed into each of 10 vials with 5 g of grain of a genotype. Intact whole grains were chosen for the experiment. The initial five weevils were marked with white correction fluid (Liquid Paper, Bellwood, IL) on the day of infestation of each genotype to distinguish the initial weevils from their progeny. Each day newly emerged maize weevils were obtained by pouring the weevils and popcorn from the jars into a sieve (4-mm diameter) that allowed the weevils to pass through the holes in the sieve and collect on a paper plate set on a chilling table (Laboratory Chill Table Model# 1431, BioQuip Products, Rancho Dominguez, CA) to cool the weevils and prevent them from flying away. The maize weevils were put into Petri dishes. A dissecting microscope was used to aid in determining the gender of the weevils. A male maize weevil has a shorter, thicker, and rougher snout than a female (Wilbur and Mills 1985). Also, when viewed in profile, the tip of the abdomen of a male maize weevil curves downward while that of a female extends straight back. Each vial with sorghum grain was closed by a small piece of organdy cloth tied over the top of the vial by a small rubber band. Each day, a set of 10 vials of each genotype was set up. Ten vials represented 10 replications for each genotype/treatment. The experimental design was completely randomized with the vials placed randomly. The vials were placed on a table with a 15.1-liter ultrasonic humidifier (Holmes Air, Model HM-600, Holmes Products Corporation, MA) under a plastic-covered cage to maintain relative humidity at approximately 65–70% and temperature at 25–27°C throughout the experiment. The study was carried out under natural photoperiod. The maize weevils and grain in each of the 10 vials of each genotype were scored once every 3 wk for a total of five times during 105 d after the grain in the vials had been infested with weevils. During 105 d, the maize weevils fed on the grain, mated, and laid eggs to produce new progeny. Each day 10 vials of maize weevils and grain of one genotype were observed and returned to the covered cage. Maize weevils and sorghum grains were poured into a Petri dish on ice to collect adults. A camel-hair brush was used to sort the maize weevils from the grain. The grain was put back into the vial and weighed. After weighing, the grain was placed on a dish, and each kernel examined with the aid of a dissecting microscope to determine the amount of damage. A scale of 1 to 5 was used to score damage by maize weevils to the grain, where 1 = no evidence of feeding; 2 = some feeding such as one hole on the surface but not all the way through the grain (1–25% of the grain damaged); 3 = two tunnels through the grain (26–50% damaged); 4 = more than two holes and/or grain was 51–75% damaged; and 5 = many feeding tunnels in grain (76–100% damaged). The weevils collected in the Petri dishes set on the chilling table were observed with the aid of a dissecting microscope. The numbers of live and dead weevils were counted in each of the 10 vials. After observation, the live weevils were returned to the vial with the sorghum grain, and the top of the vial was covered by organdy cloth fastened by a rubber band. At each observation period, the number of live weevils, number of dead weevils of the initial marked population, damage score, and weight of the grain were recorded. Data were analyzed by analysis of variance (ANOVA) using Agricultural Research Manager Program (GDMInc. 2017). After initial analysis, data were transformed using square root of X + 0.5 to meet the homogeneity of variance assumption of ANOVA. Multiple comparisons among treatment means were determined using Student–Newman–Keuls test. Percent grain weight loss for treatments was calculated using the formula: [(initial weight (5 g) − final weight excluding weevils)/initial weight] × 100. In addition to the overall ANOVA, correlation and regression analyses were used to examine relationship between kernel weight and number of live weevils, kernel weight and damage score, and kernel weight and grain weight loss at 105 d after infestation. The best-fit models were selected from linear, quadratics, and cubic models on the basis of R2 values. All statistical differences were determined using α level 0.05. Results Number of Weevils The total number of live maize weevils per vial at 63 (F = 6.86; df = 25, 229; P = 0.0001), 84 (F = 5.24; df = 25, 229; P = 0.0001), and 105 (F = 4.41; df = 25, 229; P = 0.0001) d after infestation differed significantly among the 26 genotypes of sorghum (Table 2). Genotypes B.HF8 and (A964*P850029)-HW6 consistently showed highest numbers of maize weevil per vial at 63, 84, and 105 d after infestation. Fewest maize weevils were in grain of (SV1*Sima/IS2325)-LG15 at 63 and 84 d after infestation and Sureño at 105 d after infestation. Table 2. Mean number of live maize weevils per vial at 63, 84, and 105 d after infestation Sorghum genotype*  Number of live weevils† per vial days after infestation of grain  63 d  84 d  105 d  1  23.70gh  32.80e  35.30d  2  37.20c–h  53.70cde  60.70bcd  3  49.30b–g  70.60be  90.40a–d  4  59.70a–f  80.40a–d  92.00a–d  5  30.20d–h  39.00de  38.50d  6  61.20a–e  77.41a–e  89.15a–d  7  89.20a  117.60ab  128.80ab  8  74.92abc  95.31a–d  107.6abc  9  39.50c–h  50.00cde  60.40bcd  10  54.70b–g  68.00b–e  77.50a–d  11  44.40b–h  64.70b–e  80.30a–d  12  39.70c–h  62.80b–e  72.20a–d  13  62.90a–d  93.10abc  114.30ab  14  31.58d–h  49.56cde  60.26bcd  15  32.90d–h  55.80cde  81.90a–d  16  28.20e–h  48.90cde  67.70bcd  17  76.2 ab  126.60a  135.50a  18  32.80d–h  56.90cde  80.10a–d  19  42.10c–h  74.00b–e  110.20ab  20  18.30h  32.10e  47.70cd  21  26.14e–h  52.90cde  76.94a–d  22  25.66fgh  47.80cde  65.10bcd  23  17.20h  29.97e  45.04cd  24  42.10b–h  82.70ad  103.40ab  25  33.40d–h  68.00b–e  88.90a–d  26  33.80d–h  61.30cde  80.20a–d  LSD  13.48–24.74  22.31–37.38  27.65–42.94  P  0.0001  0.0001  0.0001  Sorghum genotype*  Number of live weevils† per vial days after infestation of grain  63 d  84 d  105 d  1  23.70gh  32.80e  35.30d  2  37.20c–h  53.70cde  60.70bcd  3  49.30b–g  70.60be  90.40a–d  4  59.70a–f  80.40a–d  92.00a–d  5  30.20d–h  39.00de  38.50d  6  61.20a–e  77.41a–e  89.15a–d  7  89.20a  117.60ab  128.80ab  8  74.92abc  95.31a–d  107.6abc  9  39.50c–h  50.00cde  60.40bcd  10  54.70b–g  68.00b–e  77.50a–d  11  44.40b–h  64.70b–e  80.30a–d  12  39.70c–h  62.80b–e  72.20a–d  13  62.90a–d  93.10abc  114.30ab  14  31.58d–h  49.56cde  60.26bcd  15  32.90d–h  55.80cde  81.90a–d  16  28.20e–h  48.90cde  67.70bcd  17  76.2 ab  126.60a  135.50a  18  32.80d–h  56.90cde  80.10a–d  19  42.10c–h  74.00b–e  110.20ab  20  18.30h  32.10e  47.70cd  21  26.14e–h  52.90cde  76.94a–d  22  25.66fgh  47.80cde  65.10bcd  23  17.20h  29.97e  45.04cd  24  42.10b–h  82.70ad  103.40ab  25  33.40d–h  68.00b–e  88.90a–d  26  33.80d–h  61.30cde  80.20a–d  LSD  13.48–24.74  22.31–37.38  27.65–42.94  P  0.0001  0.0001  0.0001  Means followed by the same letter in a column are not significantly different (α = 0.05). Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. †Live weevils include all progeny and any still alive of the original five maize weevils per vial. View Large Table 2. Mean number of live maize weevils per vial at 63, 84, and 105 d after infestation Sorghum genotype*  Number of live weevils† per vial days after infestation of grain  63 d  84 d  105 d  1  23.70gh  32.80e  35.30d  2  37.20c–h  53.70cde  60.70bcd  3  49.30b–g  70.60be  90.40a–d  4  59.70a–f  80.40a–d  92.00a–d  5  30.20d–h  39.00de  38.50d  6  61.20a–e  77.41a–e  89.15a–d  7  89.20a  117.60ab  128.80ab  8  74.92abc  95.31a–d  107.6abc  9  39.50c–h  50.00cde  60.40bcd  10  54.70b–g  68.00b–e  77.50a–d  11  44.40b–h  64.70b–e  80.30a–d  12  39.70c–h  62.80b–e  72.20a–d  13  62.90a–d  93.10abc  114.30ab  14  31.58d–h  49.56cde  60.26bcd  15  32.90d–h  55.80cde  81.90a–d  16  28.20e–h  48.90cde  67.70bcd  17  76.2 ab  126.60a  135.50a  18  32.80d–h  56.90cde  80.10a–d  19  42.10c–h  74.00b–e  110.20ab  20  18.30h  32.10e  47.70cd  21  26.14e–h  52.90cde  76.94a–d  22  25.66fgh  47.80cde  65.10bcd  23  17.20h  29.97e  45.04cd  24  42.10b–h  82.70ad  103.40ab  25  33.40d–h  68.00b–e  88.90a–d  26  33.80d–h  61.30cde  80.20a–d  LSD  13.48–24.74  22.31–37.38  27.65–42.94  P  0.0001  0.0001  0.0001  Sorghum genotype*  Number of live weevils† per vial days after infestation of grain  63 d  84 d  105 d  1  23.70gh  32.80e  35.30d  2  37.20c–h  53.70cde  60.70bcd  3  49.30b–g  70.60be  90.40a–d  4  59.70a–f  80.40a–d  92.00a–d  5  30.20d–h  39.00de  38.50d  6  61.20a–e  77.41a–e  89.15a–d  7  89.20a  117.60ab  128.80ab  8  74.92abc  95.31a–d  107.6abc  9  39.50c–h  50.00cde  60.40bcd  10  54.70b–g  68.00b–e  77.50a–d  11  44.40b–h  64.70b–e  80.30a–d  12  39.70c–h  62.80b–e  72.20a–d  13  62.90a–d  93.10abc  114.30ab  14  31.58d–h  49.56cde  60.26bcd  15  32.90d–h  55.80cde  81.90a–d  16  28.20e–h  48.90cde  67.70bcd  17  76.2 ab  126.60a  135.50a  18  32.80d–h  56.90cde  80.10a–d  19  42.10c–h  74.00b–e  110.20ab  20  18.30h  32.10e  47.70cd  21  26.14e–h  52.90cde  76.94a–d  22  25.66fgh  47.80cde  65.10bcd  23  17.20h  29.97e  45.04cd  24  42.10b–h  82.70ad  103.40ab  25  33.40d–h  68.00b–e  88.90a–d  26  33.80d–h  61.30cde  80.20a–d  LSD  13.48–24.74  22.31–37.38  27.65–42.94  P  0.0001  0.0001  0.0001  Means followed by the same letter in a column are not significantly different (α = 0.05). Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. †Live weevils include all progeny and any still alive of the original five maize weevils per vial. View Large The cumulative total number of dead maize weevils from the initial population of five weevils per vial differed significantly at 63 (F = 1.85; df = 25, 226; P = 0.0105), 84 (F = 2.52; df = 25, 225; P = 0.0002), and 105 (F = 2.59; df = 25, 229; P = 0.0001) d after infestation. Of the original population of five weevils per vial, grain of (B35*B9501)-HD9 had highest number of dead weevils at 63 d after infestation (Table 3). At 84 and 105 d after infestation, grain of VG153*(TAM428*SBIII)-23 had the highest number of dead weevils. Fewest of the original maize weevils were dead in grain of (5BRON151*Tegemeo)-HG1 at 63 and 105 d of infestation and (A964*P850029)-HW6 at 84 d after infestation. Table 3. Mean cumulative number of dead maize weevils from the original population at 63, 84, and 105 d after infestation. Sorghum genotype*  Number of dead weevils/vial days after infestation of grain  63 d  84 d  105 d  1  2.30ab  2.60ab  3.40abc  2  1.40ab  1.40ab  2.40abc  3  2.00ab  2.10ab  2.70abc  4  2.00ab  2.10ab  2.40abc  5  3.30a  3.30a  4.10ab  6  1.90ab  2.04ab  2.62abc  7  1.40ab  1.50ab  2.40abc  8  1.67ab  2.00ab  3.11abc  9  1.70ab  3.40a  4.40a  10  2.20ab  2.30ab  3.20abc  11  0.90b  1.10b  2.10abc  12  1.20ab  1.40ab  2.80abc  13  1.10b  1.30ab  2.10bc  14  1.16b  1.43ab  2.45abc  15  1.50ab  1.60ab  2.20abc  16  1.60ab  1.70ab  2.90abc  17  0.91b  1.03b  1.87c  18  1.70ab  1.90ab  2.20abc  19  1.00b  1.20b  1.40c  20  2.10ab  2.40ab  2.70abc  21  1.79ab  1.99ab  3.20abc  22  1.57ab  1.70ab  1.98bc  23  2.01ab  2.45ab  2.68abc  24  1.20ab  1.30ab  1.80bc  25  1.60ab  1.70ab  3.30abc  26  1.60ab  1.80ab  2.90abc  LSD  0.96–1.28  0.97–1.30  1.05–1.45  P  0.0105  0.0002  0.0001  Sorghum genotype*  Number of dead weevils/vial days after infestation of grain  63 d  84 d  105 d  1  2.30ab  2.60ab  3.40abc  2  1.40ab  1.40ab  2.40abc  3  2.00ab  2.10ab  2.70abc  4  2.00ab  2.10ab  2.40abc  5  3.30a  3.30a  4.10ab  6  1.90ab  2.04ab  2.62abc  7  1.40ab  1.50ab  2.40abc  8  1.67ab  2.00ab  3.11abc  9  1.70ab  3.40a  4.40a  10  2.20ab  2.30ab  3.20abc  11  0.90b  1.10b  2.10abc  12  1.20ab  1.40ab  2.80abc  13  1.10b  1.30ab  2.10bc  14  1.16b  1.43ab  2.45abc  15  1.50ab  1.60ab  2.20abc  16  1.60ab  1.70ab  2.90abc  17  0.91b  1.03b  1.87c  18  1.70ab  1.90ab  2.20abc  19  1.00b  1.20b  1.40c  20  2.10ab  2.40ab  2.70abc  21  1.79ab  1.99ab  3.20abc  22  1.57ab  1.70ab  1.98bc  23  2.01ab  2.45ab  2.68abc  24  1.20ab  1.30ab  1.80bc  25  1.60ab  1.70ab  3.30abc  26  1.60ab  1.80ab  2.90abc  LSD  0.96–1.28  0.97–1.30  1.05–1.45  P  0.0105  0.0002  0.0001  Means followed by the same letter in a column are not significantly different (α = 0.05). Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. View Large Table 3. Mean cumulative number of dead maize weevils from the original population at 63, 84, and 105 d after infestation. Sorghum genotype*  Number of dead weevils/vial days after infestation of grain  63 d  84 d  105 d  1  2.30ab  2.60ab  3.40abc  2  1.40ab  1.40ab  2.40abc  3  2.00ab  2.10ab  2.70abc  4  2.00ab  2.10ab  2.40abc  5  3.30a  3.30a  4.10ab  6  1.90ab  2.04ab  2.62abc  7  1.40ab  1.50ab  2.40abc  8  1.67ab  2.00ab  3.11abc  9  1.70ab  3.40a  4.40a  10  2.20ab  2.30ab  3.20abc  11  0.90b  1.10b  2.10abc  12  1.20ab  1.40ab  2.80abc  13  1.10b  1.30ab  2.10bc  14  1.16b  1.43ab  2.45abc  15  1.50ab  1.60ab  2.20abc  16  1.60ab  1.70ab  2.90abc  17  0.91b  1.03b  1.87c  18  1.70ab  1.90ab  2.20abc  19  1.00b  1.20b  1.40c  20  2.10ab  2.40ab  2.70abc  21  1.79ab  1.99ab  3.20abc  22  1.57ab  1.70ab  1.98bc  23  2.01ab  2.45ab  2.68abc  24  1.20ab  1.30ab  1.80bc  25  1.60ab  1.70ab  3.30abc  26  1.60ab  1.80ab  2.90abc  LSD  0.96–1.28  0.97–1.30  1.05–1.45  P  0.0105  0.0002  0.0001  Sorghum genotype*  Number of dead weevils/vial days after infestation of grain  63 d  84 d  105 d  1  2.30ab  2.60ab  3.40abc  2  1.40ab  1.40ab  2.40abc  3  2.00ab  2.10ab  2.70abc  4  2.00ab  2.10ab  2.40abc  5  3.30a  3.30a  4.10ab  6  1.90ab  2.04ab  2.62abc  7  1.40ab  1.50ab  2.40abc  8  1.67ab  2.00ab  3.11abc  9  1.70ab  3.40a  4.40a  10  2.20ab  2.30ab  3.20abc  11  0.90b  1.10b  2.10abc  12  1.20ab  1.40ab  2.80abc  13  1.10b  1.30ab  2.10bc  14  1.16b  1.43ab  2.45abc  15  1.50ab  1.60ab  2.20abc  16  1.60ab  1.70ab  2.90abc  17  0.91b  1.03b  1.87c  18  1.70ab  1.90ab  2.20abc  19  1.00b  1.20b  1.40c  20  2.10ab  2.40ab  2.70abc  21  1.79ab  1.99ab  3.20abc  22  1.57ab  1.70ab  1.98bc  23  2.01ab  2.45ab  2.68abc  24  1.20ab  1.30ab  1.80bc  25  1.60ab  1.70ab  3.30abc  26  1.60ab  1.80ab  2.90abc  LSD  0.96–1.28  0.97–1.30  1.05–1.45  P  0.0105  0.0002  0.0001  Means followed by the same letter in a column are not significantly different (α = 0.05). Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. View Large Damage Score The mean damage score of the 26 sorghum genotypes at 21 (F = 23.11; df = 25, 229; P = 0.0001), 42 (F = 10.43; df = 25, 229; P = 0.0001), 63 (F = 8.73; df = 25, 229; P = 0.0001), 84 (F = 6.92; df = 25, 229; P = 0.0001), and 105 (F = 8.21; df = 25, 229; P = 0.0001) d after infestation with maize weevils differed significantly. Sorghum genotypes Sureo, (SV1*Sima/IS23250)-LG15, (5BRON151*Tegemeo)-HG7, and (B35*B9501)-HD9 ranked among the top four genotypes with least damage rating more often than any other genotypes across the five sampling dates (Table 4). On the other hand, genotypes B.HF8, (A964*P850029)-HW6, (Segaolane*WM#322)-LG2, and (Tx2880*(Tx2880*(Tx2864*(Tx436*(Tx2864*PI550607)))))-PR3-CM1 were more often ranked among the top four genotypes with highest damage rating across the sampling dates compared to other genotypes. Table 4. Mean damage score across sorghum genotypes Sorghum genotype*  Mean damage score† days after infestation of grain  21 d  42 d  63 d  84 d  105 d  1  1.04k  1.15g  1.62fgh  1.80fg  1.88h  2  1.07jk  1.25c–g  1.89c–h  2.29c–g  2.60c–h  3  1.15d–i  1.38b–e  2.15b–f  2.71b–e  3.30b–e  4  1.09h–k  1.25d–g  2.18b–f  2.60b–f  3.32b–f  5  1.08ijk  1.18fg  1.72fgh  1.84fg  2.19e–h  6  1.09g–k  1.31b–f  2.28b–e  2.63b–f  3.29b–f  7  1.12e–j  1.42b  2.95a  3.51a  4.47a  8  1.11f–j  1.35b–e  2.43bc  3.12abc  3.79a–d  9  1.10f–k  1.32b–f  1.93c–h  2.17d–g  2.62c–h  10  1.10f–k  1.29b–g  2.02b–h  2.43c–g  3.00c–g  11  1.15d–j  1.41bc  2.08b–g  2.44c–g  3.18b–g  12  1.12f–j  1.28b–g  1.85d–h  2.18d–g  2.77c–h  13  1.18c–f  1.39bcd  2.33bcd  2.82a–e  4.21ab  14  1.15d–j  1.29b–g  1.84d–h  2.15d–g  2.56c–h  15  1.17c–h  1.38b–e  1.98c–h  2.34c–g  3.16b–g  16  1.13e–j  1.33b–f  1.76e–h  1.99efg  2.49d–h  17  1.20cde  1.42b  2.40bc  3.28ab  4.63a  18  1.11f–j  1.23efg  1.67fgh  2.18d–g  2.80c–h  19  1.17c–g  1.32b–f  1.98c–h  2.38c–g  3.58a–d  20  1.13e–j  1.24d–g  1.54h  1.73g  2.13fgh  21  1.23c  1.37b–e  1.77e–h  2.12d–g  2.56c–h  22  1.23c  1.34b–e  1.81d–h  2.09d–g  2.73c–h  23  1.15d–j  1.23efg  1.58gh  1.74g  2.08gh  24  1.44a  1.69a  2.51b  2.90a–d  3.75abc  25  1.30b  1.36b–e  1.86d–h  2.45c–g  3.13b–g  26  1.22cd  1.30b–f  1.82d–h  2.33c–g  3.08b–g  LSD  0.05  0.08–0.09  0.28–0.34  0.43–0.53  0.59–0.79  P  0.0001  0.0001  0.0001  0.0001  0.0001  Sorghum genotype*  Mean damage score† days after infestation of grain  21 d  42 d  63 d  84 d  105 d  1  1.04k  1.15g  1.62fgh  1.80fg  1.88h  2  1.07jk  1.25c–g  1.89c–h  2.29c–g  2.60c–h  3  1.15d–i  1.38b–e  2.15b–f  2.71b–e  3.30b–e  4  1.09h–k  1.25d–g  2.18b–f  2.60b–f  3.32b–f  5  1.08ijk  1.18fg  1.72fgh  1.84fg  2.19e–h  6  1.09g–k  1.31b–f  2.28b–e  2.63b–f  3.29b–f  7  1.12e–j  1.42b  2.95a  3.51a  4.47a  8  1.11f–j  1.35b–e  2.43bc  3.12abc  3.79a–d  9  1.10f–k  1.32b–f  1.93c–h  2.17d–g  2.62c–h  10  1.10f–k  1.29b–g  2.02b–h  2.43c–g  3.00c–g  11  1.15d–j  1.41bc  2.08b–g  2.44c–g  3.18b–g  12  1.12f–j  1.28b–g  1.85d–h  2.18d–g  2.77c–h  13  1.18c–f  1.39bcd  2.33bcd  2.82a–e  4.21ab  14  1.15d–j  1.29b–g  1.84d–h  2.15d–g  2.56c–h  15  1.17c–h  1.38b–e  1.98c–h  2.34c–g  3.16b–g  16  1.13e–j  1.33b–f  1.76e–h  1.99efg  2.49d–h  17  1.20cde  1.42b  2.40bc  3.28ab  4.63a  18  1.11f–j  1.23efg  1.67fgh  2.18d–g  2.80c–h  19  1.17c–g  1.32b–f  1.98c–h  2.38c–g  3.58a–d  20  1.13e–j  1.24d–g  1.54h  1.73g  2.13fgh  21  1.23c  1.37b–e  1.77e–h  2.12d–g  2.56c–h  22  1.23c  1.34b–e  1.81d–h  2.09d–g  2.73c–h  23  1.15d–j  1.23efg  1.58gh  1.74g  2.08gh  24  1.44a  1.69a  2.51b  2.90a–d  3.75abc  25  1.30b  1.36b–e  1.86d–h  2.45c–g  3.13b–g  26  1.22cd  1.30b–f  1.82d–h  2.33c–g  3.08b–g  LSD  0.05  0.08–0.09  0.28–0.34  0.43–0.53  0.59–0.79  P  0.0001  0.0001  0.0001  0.0001  0.0001  Means followed by the same letter in a column are not significantly different. Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. †Damage was scored on a scale of 1–5, where 1 = no evidence of feeding; 2 = some feeding at surface such as one feeding hole but not all the way through the grain (involving 1–25% of the grain); 3 = two tunnels through the grain (26–50% damaged); 4 = more than two holes and/or grain was 51–75% damaged; 5 = many feeding tunnels in grain (76–100% damaged). View Large Table 4. Mean damage score across sorghum genotypes Sorghum genotype*  Mean damage score† days after infestation of grain  21 d  42 d  63 d  84 d  105 d  1  1.04k  1.15g  1.62fgh  1.80fg  1.88h  2  1.07jk  1.25c–g  1.89c–h  2.29c–g  2.60c–h  3  1.15d–i  1.38b–e  2.15b–f  2.71b–e  3.30b–e  4  1.09h–k  1.25d–g  2.18b–f  2.60b–f  3.32b–f  5  1.08ijk  1.18fg  1.72fgh  1.84fg  2.19e–h  6  1.09g–k  1.31b–f  2.28b–e  2.63b–f  3.29b–f  7  1.12e–j  1.42b  2.95a  3.51a  4.47a  8  1.11f–j  1.35b–e  2.43bc  3.12abc  3.79a–d  9  1.10f–k  1.32b–f  1.93c–h  2.17d–g  2.62c–h  10  1.10f–k  1.29b–g  2.02b–h  2.43c–g  3.00c–g  11  1.15d–j  1.41bc  2.08b–g  2.44c–g  3.18b–g  12  1.12f–j  1.28b–g  1.85d–h  2.18d–g  2.77c–h  13  1.18c–f  1.39bcd  2.33bcd  2.82a–e  4.21ab  14  1.15d–j  1.29b–g  1.84d–h  2.15d–g  2.56c–h  15  1.17c–h  1.38b–e  1.98c–h  2.34c–g  3.16b–g  16  1.13e–j  1.33b–f  1.76e–h  1.99efg  2.49d–h  17  1.20cde  1.42b  2.40bc  3.28ab  4.63a  18  1.11f–j  1.23efg  1.67fgh  2.18d–g  2.80c–h  19  1.17c–g  1.32b–f  1.98c–h  2.38c–g  3.58a–d  20  1.13e–j  1.24d–g  1.54h  1.73g  2.13fgh  21  1.23c  1.37b–e  1.77e–h  2.12d–g  2.56c–h  22  1.23c  1.34b–e  1.81d–h  2.09d–g  2.73c–h  23  1.15d–j  1.23efg  1.58gh  1.74g  2.08gh  24  1.44a  1.69a  2.51b  2.90a–d  3.75abc  25  1.30b  1.36b–e  1.86d–h  2.45c–g  3.13b–g  26  1.22cd  1.30b–f  1.82d–h  2.33c–g  3.08b–g  LSD  0.05  0.08–0.09  0.28–0.34  0.43–0.53  0.59–0.79  P  0.0001  0.0001  0.0001  0.0001  0.0001  Sorghum genotype*  Mean damage score† days after infestation of grain  21 d  42 d  63 d  84 d  105 d  1  1.04k  1.15g  1.62fgh  1.80fg  1.88h  2  1.07jk  1.25c–g  1.89c–h  2.29c–g  2.60c–h  3  1.15d–i  1.38b–e  2.15b–f  2.71b–e  3.30b–e  4  1.09h–k  1.25d–g  2.18b–f  2.60b–f  3.32b–f  5  1.08ijk  1.18fg  1.72fgh  1.84fg  2.19e–h  6  1.09g–k  1.31b–f  2.28b–e  2.63b–f  3.29b–f  7  1.12e–j  1.42b  2.95a  3.51a  4.47a  8  1.11f–j  1.35b–e  2.43bc  3.12abc  3.79a–d  9  1.10f–k  1.32b–f  1.93c–h  2.17d–g  2.62c–h  10  1.10f–k  1.29b–g  2.02b–h  2.43c–g  3.00c–g  11  1.15d–j  1.41bc  2.08b–g  2.44c–g  3.18b–g  12  1.12f–j  1.28b–g  1.85d–h  2.18d–g  2.77c–h  13  1.18c–f  1.39bcd  2.33bcd  2.82a–e  4.21ab  14  1.15d–j  1.29b–g  1.84d–h  2.15d–g  2.56c–h  15  1.17c–h  1.38b–e  1.98c–h  2.34c–g  3.16b–g  16  1.13e–j  1.33b–f  1.76e–h  1.99efg  2.49d–h  17  1.20cde  1.42b  2.40bc  3.28ab  4.63a  18  1.11f–j  1.23efg  1.67fgh  2.18d–g  2.80c–h  19  1.17c–g  1.32b–f  1.98c–h  2.38c–g  3.58a–d  20  1.13e–j  1.24d–g  1.54h  1.73g  2.13fgh  21  1.23c  1.37b–e  1.77e–h  2.12d–g  2.56c–h  22  1.23c  1.34b–e  1.81d–h  2.09d–g  2.73c–h  23  1.15d–j  1.23efg  1.58gh  1.74g  2.08gh  24  1.44a  1.69a  2.51b  2.90a–d  3.75abc  25  1.30b  1.36b–e  1.86d–h  2.45c–g  3.13b–g  26  1.22cd  1.30b–f  1.82d–h  2.33c–g  3.08b–g  LSD  0.05  0.08–0.09  0.28–0.34  0.43–0.53  0.59–0.79  P  0.0001  0.0001  0.0001  0.0001  0.0001  Means followed by the same letter in a column are not significantly different. Statistics were generated on transformed data (square root of X + 0.5). Tabular values are actual data. LSD = least significant difference. *See Table 1 for genotype pedigree. †Damage was scored on a scale of 1–5, where 1 = no evidence of feeding; 2 = some feeding at surface such as one feeding hole but not all the way through the grain (involving 1–25% of the grain); 3 = two tunnels through the grain (26–50% damaged); 4 = more than two holes and/or grain was 51–75% damaged; 5 = many feeding tunnels in grain (76–100% damaged). View Large Weight Loss Weight of the sorghum grain differed significantly among the 26 genotypes at 105 (F = 3.81; df = 25, 229; P = 0.0001) d after infestation with maize weevils (Fig. 1). The least percentages of weight loss of 23.88 and 24.11% were recorded for sorghum genotypes Sureño and (5BRON151*Tegemeo)-HG7, respectively. Genotypes B.HF8 and (A964*P850029)-HW6 had lost most weight, 70.62 and 67.69%, at 105 d after infestation by maize weevils. There was no strong relationship between kernel weight and number of live weevils (R2 = 0.02, P = 0.0223). Also, no significant relationship was found between kernel weight and damage score (R2 = 0.01, P = 0.1105), and kernel weight and grain weight loss (R2 = 0.0029, P = 0.3929). Discussion Sorghum genotypes used in the study showed a wide range of resistance and susceptibility to maize weevil. Genotypes Sureño, (5BRON151*Tegemeo)-HG7, (SV1*Sima/IS23250)-LG15, and (B35*B9501)-HD9 were the most resistant to maize weevils as they had least number of live weevils, damage score, and grain weight loss. On the other hand, number of live weevils, damage score, and weight loss were highest in genotypes B.HF8, (A964*P850029)-HW6, (9MLT176*A964)-LG8, and (Segaolane*WM#322)-LG2 indicating their susceptibility to maize weevil. These genotypes favored survival and emergence of large number of maize weevils throughout the experimental period. All remaining sorghum genotypes exhibited intermediate levels of resistance against maize weevil. Our results agree with that of Chitio (2004) study that showed resistance of Sureño grain to maize weevil (Chitio et al. 2004). Genotypes evaluated in the current study are primarily developed for improved agronomic reasons such as drought tolerance, resistance to insect pests in field, and improved grain quality. Significant variability in level of resistance to maize weevil among these genotypes set a stage for follow-up studies to investigate mechanisms of postharvest resistance to stored grain pests. Use of resistant sorghum genotypes can be an effective strategy to reduce food grain losses especially in the developing world where substantial food grain losses occur to storage insect pests due to inadequate storage facilities. Initial steps in development of insect-resistant cultivars include the identification of resistant sources and the mechanisms of resistance. Plants exhibit resistance to insect pests through different mechanisms, which includes antibiosis (the plant affects insect pest biology adversely), antixenosis (the plant is not a preferred host), and tolerance (the plant has the ability to withstand or recover from insect damage and produces normal yield) (Smith 1989). In the current study, we evaluated sorghum genotypes for resistance to maize weevil by determining weevil survival and mortality, damage rating, and grain weight loss by artificially infesting grain of each genotype with maize weevils under laboratory conditions. However, little emphasis was given toward investigating the mechanisms of resistance to maize weevil. Therefore, future studies should be conducted to elucidate mechanisms(s) of resistance in sorghum genotypes to maize weevil. Chemical composition of seed can be studied to determine whether antibiotic activity (antibiosis) exists in resistant genotypes such as Sureño. Several studies have shown that certain chemical composition and/or physical properties of grain could make it favorable or less favorable to survival and reproduction of maize weevil (Russell 1962, Doraiswamy 1976, Adetunji 1988, Reddy 2002). Adetunji (1988) found sorghum grain resistance to Sitophilus oryzae (L.) to be associated with greater larval mortality, longer developmental periods (antibiosis), and reduced oviposition (nonpreference). Phenolic acids have been studied extensively as biochemical components correlated with maize weevil resistance in maize (Arnason et al. 1997). Also, susceptibility to maize weevil has been related to nutritional quality traits such as sugar, protein, fat, and amino acids in maize (Dobie 1977, Classen et al. 1990). Physical factors such as grain hardness and pericarp surface texture can also impart resistance or susceptibility to maize weevil (Doraiswamy 1976, Dobie 1977, García-Lara et al. 2004). Seed size has been reported to influence the level of resistance and susceptibility to stored-grain pests (Mills 1985, Wongo 1990). In the current study, however, no correlation between kernel weight and the level of resistance to maize weevil was found. Pendleton et al. (2011) examined maize weevil resistant sorghum genotypes using a scanning electronic microscope and demonstrated a positive correlation between the depth of a band of concentrated iodine (with bound starch) measured from the seed coat and the degree of resistance to damage by the maize weevil (Pendleton et al. 2011, 2012). Similar investigations can be done on the sorghum genotypes studied in the current study to determine whether correlation exists between any of the physical or chemical properties of grain and the resistance to the maize weevil. Despite the substantial sorghum grain losses to stored-grain pests such as maize weevil, little emphasis has been given toward developing commercial cultivars with postharvest resistance to stored-grain insect pests. Under the circumstances, studies on identifying resistant sources and understanding mechanisms of resistance will help developing commercial sorghum cultivars resistant to stored-grain insect pests through traditional and molecular breeding techniques. To summarize, this study provides information on the level of resistance among selected sorghum genotypes to maize weevil. Research to identify maize weevil–resistant germplasm and traits associated with resistance needs to be continued to facilitate development of maize weevil–resistant sorghum. Development of commercial sorghum cultivars resistant to maize weevil will help reduce grain losses especially in developing countries where storage structures and resources to manage stored-grain pests are scarce. Fig. 1. View largeDownload slide Percentage of weight loss of sorghum grain at 105 d after infestation with maize weevils (weight without weevils). Bars showing same letter are not significantly different (α = 0.05). The figure is based on untransformed data while statistics were generated on square root of (X + 0.5) transformed data. See Table 1 for genotype pedigree. Fig. 1. View largeDownload slide Percentage of weight loss of sorghum grain at 105 d after infestation with maize weevils (weight without weevils). Bars showing same letter are not significantly different (α = 0.05). The figure is based on untransformed data while statistics were generated on square root of (X + 0.5) transformed data. See Table 1 for genotype pedigree. Acknowledgments This work was financially supported in part by the International Sorghum, Millet and Other Grains Collaborative Research Support Program (INTSORMIL CRSP). References Cited Adetunji, J. F. 1988. 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Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

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Environmental EntomologyOxford University Press

Published: Apr 9, 2018

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