TY - JOUR
AU1 - Klein,, Coby
AU2 - Baker,, Mitchell
AU3 - Alyokhin,, Andrei
AU4 - Mota-Sanchez,, David
AB - Abstract Eastern New York State is frequently the site of Colorado potato beetle (Leptinotarsa decemlineata, Say) populations with the highest observed levels of insecticide resistance to a range of active ingredients. The dominance of a resistant phenotype will affect its rate of increase and the potential for management. On organic farms on Long Island, L. decemlineata evolved high levels of resistance to spinosad in a short period of time and that resistance has spread across the eastern part of the Island. Resistance has also emerged in other parts of the country as well. To clarify the level of dominance or recessiveness of spinosad resistance in different parts of the United States and how resistance differs in separate beetle populations, we sampled in 2010 beetle populations from Maine, Michigan, and Long Island. In addition, a highly resistant Long Island population was assessed in 2012. All populations were hybridized with a laboratory-susceptible strain to determine dominance. None of the populations sampled in 2010 were significantly different from additive resistance, but the Long Island population sampled in 2012 was not significantly different from fully recessive. Recessive inheritance of high-level resistance may help manage its increase. spinosad, resistance, dominance, recessive, geographic variation Under strong selection pressure from insecticides, resistance can evolve rapidly (Brevik et al. 2018), and resistance is very costly in terms of crop losses and potential health effects. Colorado potato beetles (Leptinotarsa decemlineata, Say) in Michigan developed resistance to multiple insecticides in widespread areas in a span of about 5 yr (Grafius 1997) and became resistant to several insecticide types on Long Island in a similar time frame (Georghiou 1986; Mota-Sanchez and Wise 2020). Intensification of potato farming and the accompanying increase in pesticide use, and a lack of crop rotation are major factors in the rapid development of resistance. The dominance of a resistant phenotype is another key factor that determines how resistance can spread. Dominance is the measure of the relative expression of the phenotype of the heterozygote relative to the phenotype of the two corresponding homozygotes (Bourguet et al. 2000). The level of dominance of resistance to a single dose of insecticide is often inversely related to the concentration of the dose to which the insects are exposed and can also be altered by the environment (Liu and Tabashnik 1997, Sayyed et al. 2000, Tabashnik et al. 2004, Szendrei et al. 2011). Dominance can also vary based on the number of genetic loci responsible for conferring resistance. With polygenic resistance, each gene is contributing a portion to resistance, and heterozygote offspring may not possess every resistance gene, so resistance will reflect the impacts of multiple loci and will be closer to additive. Since monogenic resistance is more likely to arise in the field where population sizes are much larger than in small, laboratory-selected strains (Roush and McKenzie 1987), the probability of a single resistance mutation of large effect appearing in the field is much greater than in a small laboratory population. A single gene with a large effect will spread more quickly than a polygenic trait (Hoy et al. 1980). The high-dose-refuge strategy of resistance management is built on the idea that recessive, monogenic resistance can be delayed if treated properly. Development of resistance can theoretically be delayed if fields are initially treated with a high enough dose of pesticides to kill heterozygotes, and untreated refuge areas can provide a source of susceptible genes to the treated fields (Roush and McKenzie 1987). Over time, however, dominance can change with the evolution of dominance modifiers. These modifiers can act on one or more traits and effectively increase the dominance level of resistance (Bourguet et al. 2000). For example, a dominance modifier has been documented in DDT-resistant house flies (Musca domestica, Linnaeus, Diptera: Muscidae). When the modifier gene is present, the levels of both resistance and dominance are increased (Grigolo and Oppenoorth 1966). Recommendations on resistance management are commonly developed based on studies of as little as one resistant strain, sometimes a single laboratory-selected strain. Resistance mechanisms may be diverse even within a relatively limited geographic area (Ioannidis et al. 1991). Geographic variation in resistance and dominance shortly after a new product is introduced may indicate multiple origins of resistance, and different genetic mechanisms underlying resistance in different areas. In addition to guiding local management, it can also give insight into the progression of resistance evolution. Potato farms on Long Island have been dealing with insecticide resistance for decades. The first documented failure of pesticides on the Island was in the 1940s (Gauthier et al. 1981). Since then, every newly introduced product has failed, often in just a few years. In certain cases, L. decemlineata showed signs of resistance to pesticides before they were even available for use by the public (Grafius 1997, Olson et al. 2000, Mota-Sanchez et al. 2006). High levels of resistance to neonicotinoid insecticides have been present on Long Island farms for more than 20 yr with resistance being autosomal and either partially recessive or partially dominant (Zhao et al. 2000, Baker et al. 2007, Alyokhin et al. 2008). It is theorized that the high selection pressure caused by excessive pesticide use, low gene flow due to geographic isolation, and a favorable climate—both in terms of high reproductive capabilities and low overwintering mortality—contribute to this phenomenon (Alyokhin et al. 2015). Extremely high level (>5,000-fold increase in LD50 relative to a laboratory-susceptible colony) resistance to spinosad has been documented on Long Island starting in 2010 (Schnaars-Uvino 2013). Both Michigan and Maine have seen moderate to high levels of resistance to several insecticide chemistries. In Michigan, resistance by L. decemlineata to carbamates, organophosphates, and pyrethroids was strong enough in the early 1990s that rotenone and cryolite were used for the first time in decades (Roush et al. 1990). Neonicotinoids were much more effective at controlling L. decemlineata, and although resistance to this class of insecticides has been on the rise in the last decade or so, it has remained fairly low in the Midwest compared with Long Island. This is most likely due to a combination of factors including more frequent crop rotation, insecticide rotation, and fewer generations of beetles per year (Alyokhin et al. 2015). Resistance in Maine is largely a problem in a single, isolated region in the southern part of the state where growers used repeated doses of insecticides to try to curb L. decemlineata, which led to a general failure of control efforts by early 2000s. An intensive resistance management program restored some level of susceptibility to neonicotinoids in that population within a few years (Alyokhin et al. 2015). Spinosad is a natural insecticide compound, derived from the soil actinomycete Saccharopolyspora spinosa. It acts on the nicotinic acetylcholinesterase receptors of insects but at a different target site than the neonicotinoids (Sparks et al. 2012). Spinosad resistance has been detected in many different insect species. According to a review by Sparks et al. (2012), resistance to spinosad across species is typically due to monogenic, recessive mutations, although there are examples of polygenic resistance as well as incomplete dominance. For example, resistance in the thrip Frankliniella occidentallis, Pergande (Thysanoptera: Thripidae) was inherited as an incompletely dominant trait that may have been associated with more than one gene (Zhang et al. 2008). In this study, we analyze the genetics of spinosad resistance and geographic variation in dominance. We sampled beetle populations from Maine, Michigan, and Long Island in 2010, in addition to a highly resistant population from Long Island that was identified in 2012. We hybridized each to a laboratory-susceptible colony to measure the dominance of resistance from each population. This study will clarify the level of dominance or recessiveness of such mutations and show how resistance differs in separate populations of potato beetles. Materials and Methods Populations and Rearing In 2010, three field populations and one susceptible laboratory-raised line were used. Leptinotarsa decemlineata clutches or adults were collected from commercial potato fields in Riverhead, NY, Mecosta Co., MI, and Fryeburg, ME, in June 2010. All populations were reared for one to two generations in 74 × 61 × 46 cm cages under 25°C and a 16:8 (L:D) h cycle. Cages were provisioned with potted whole potato plants, and pots were replaced or watered as needed. Egg clutches were collected daily; leaves with clutches were removed from the plants and incubated at 25°C and a 16:8 (L:D) h cycle in a Percival model I-36 VL incubator (Percival Scientific, Inc., Perry, IA). Populations were initiated with either 50 field-collected clutches or 200 field-collected adults, and individual populations were maintained in the laboratory by collecting 50 clutches or 150 adults from the previous generation to inoculate a new cage. The laboratory susceptible reference strain was used that has been reared in captivity for over 20 yr since its establishment using beetles collected in New Jersey (French Agricultural Research Inc., Lamberton, MN). Mating pairs were established using virgin adults from each colony. As adults first started emerging from each colony, they were collected daily, visually sexed, segregated by gender to prevent mating, and held in single-sex groups of up to five per 325-ml vented Nalgene boxes until used to establish pairs. To measure the fecundity of the field populations and the resistance of the hybrid offspring between each field population and the reference strain, reciprocal colonies were first established using one each of field males and virgin susceptible reference females, or susceptible reference males and virgin field females, for each field population. Larvae from those colonies were reared in separate cages, and as virgin adults emerged from pupation, they were collected daily for use in this study. In 2012, a highly resistant population on Long Island was used to assess the dominance of high-level resistance. This was a field that in 2010 showed high-level resistance to spinosad (Schnaars-Uvino 2013), with a resistance ratio for LD50 of 5,750-fold, relative to the New Jersey laboratory-susceptible strain. Adults were collected from that field on the South Fork of Long Island—located approximately 38 km from the 2010 field and separated by the Peconic Bay—in June of 2012 and reared in the laboratory for one generation. Hybrids were generated by stocking cages with 10–20 resistant Long Island males with a matched number of laboratory-susceptible females or 10–20 Long Island females with a matched number of laboratory-susceptible males. Experimental Design Twelve to 18 pairs of virgin adults from each source population, the susceptible reference strain, and hybrids between each source population and the susceptible population were housed by pair in 325-ml vented Nalgene boxes (12.5 × 7 × 5.5 cm) with mesh windows for ventilation in an incubator at 25°C and a photoperiod of 16:8 (L:D) h. Each pair’s cage was maintained with fresh potato clippings mounted in floral pics changed daily. Clutches were collected and eggs counted one to two times daily for 2 wk from the first laid clutch. Individual clutches were transferred to 3.5-cm Petri dishes. Hatchlings were removed one to two times per day and pooled by population and reared until the second day of the second-instar stage for bioassay. The source population was coded, so that it would be unknown when scored for bioassay. Bioassay and Analysis Two-day-old second instars (weighing 5–8.5 mg) were assayed by direct topical application on the abdomen of a 1-µl drop of spinosad dissolved in HPLC-grade (0.995) acetone. Spinosad was extracted from SpinTor 2SC Naturalyte (Dow AgroSciences LLC) by first diluting 1:9 using HPLC-grade (0.995) acetone, then vacuum filtering twice to remove remaining particulates. The extraction used to create all solutions used in this study was confirmed by a specific immunosorbent assay performed by Environmental Micro Analysis, Inc, Woodland, CA, to have 0.59 efficiency from the stated concentration of active ingredient in the product label. Up to seven concentrations of spinosad from 4.2 × 10−3 to 1.35 × 10−1 µg/larva in 2010 and up to 12 concentrations from 4.2 × 10−3 to 42 µg/larva in 2012, plus an acetone control, were used. Following application, larvae were placed on a potato leaf-cutting and held at 25°C for 24 h until scoring. Dose–mortality curves were analyzed using Polo-Plus (LeOra Software 2007). Larvae were scored after 24 h with mortality defined as failure to move a leg for 10 s after the larva is placed on its back. We attempted to assay at least 30 individuals from each population at each dose, but if fewer were available at the correct size, we analyzed the mortality data and included the LD50 results if the index of significance for potency estimation, g (Finney 1971), was less than 0.7 at the 0.95 confidence level. The degree of dominance (D) of resistance was calculated as in Stone (1968) on a −1 to 1 scale, where −1 is fully recessive, 0 additive, and 1 fully dominant: D=(2RS−RR−SS)(RR−SS) where RS, RR, and SS are the logarithms of the LD50’s for heterozygotes, homozygote-resistant, and homozygote-susceptible strains. There were no differences between resistant female- or resistant male-hybrid colonies, so bioassay results were pooled for each colony type. Variance of D was calculated as in Preisler et al. (1990), to allow calculation of a standard error, SE=var⁡(D) ⁠, allowing a confidence interval to test whether completely recessive (−1) or dominant (1) inheritance fell within the range of estimation. Results Resistance to spinosad varied among populations, and dominance appeared negatively associated with local resistance (Table 1). Resistance ratios varied from 12.5 to 58.6 in 2010. The Michigan assays were a poor fit to the logit model and were not significantly different from any population but the control. Riverhead, NY, and Fryeburg, ME, were significantly different. The least resistant population, Fryeburg, ME, showed the highest level of dominance, 0.66 on a −1 to +1 scale. Riverhead, NY, the most resistant population, was also the least dominant, though poor fits of either the pure or hybrid strains from each geographical location prevented any of the dominance estimates from being significantly different from additive or dominant inheritance. Table 1. Resistance to spinosad of L. decemlineata from New York, Maine, and Michigan, a susceptible laboratory colony, and hybrids of each field population and the laboratory-susceptible line Population . Na . LD50b . Lowerc . Upperc . Slope . χ 2 . df . P . RRd . De . ME Freyburg 224 0.0863 0.0228 0.2807 0.623 9.99 8 0.27 12.5 0.66 ME Hybrid 506 0.0366 0.0035 0.1494 0.569 36.55 8 <0.001 5.3 Riverhead NY 342 0.4042 0.2258 0.6826 1.068 12.01 9 0.21 58.6 −0.35 NY Hybrid 245 0.0266 0.0130 0.0571 1.238 6.42 4 0.17 3.9 Michigan 250 0.1779 0.0100 1.9172 2.031 18.64 8 0.02 25.8 0.31 MI Hybrid 247 0.1034 0.0061 0.7411 0.393 4.84 6 0.56 15.0 Susceptible 217 0.0069 0.0014 0.0137 1.57 13.14 4 0.01 1.0 Population . Na . LD50b . Lowerc . Upperc . Slope . χ 2 . df . P . RRd . De . ME Freyburg 224 0.0863 0.0228 0.2807 0.623 9.99 8 0.27 12.5 0.66 ME Hybrid 506 0.0366 0.0035 0.1494 0.569 36.55 8 <0.001 5.3 Riverhead NY 342 0.4042 0.2258 0.6826 1.068 12.01 9 0.21 58.6 −0.35 NY Hybrid 245 0.0266 0.0130 0.0571 1.238 6.42 4 0.17 3.9 Michigan 250 0.1779 0.0100 1.9172 2.031 18.64 8 0.02 25.8 0.31 MI Hybrid 247 0.1034 0.0061 0.7411 0.393 4.84 6 0.56 15.0 Susceptible 217 0.0069 0.0014 0.0137 1.57 13.14 4 0.01 1.0 aNumber of second-instar larvae tested. bLD50s are in units of µg/larva. c95% fiducial limits. dLD50 of a given field population/LD50 of the susceptible laboratory line. eDominance as in Stone (1968) ranging from fully recessive (−1) to fully dominant (1). Open in new tab Table 1. Resistance to spinosad of L. decemlineata from New York, Maine, and Michigan, a susceptible laboratory colony, and hybrids of each field population and the laboratory-susceptible line Population . Na . LD50b . Lowerc . Upperc . Slope . χ 2 . df . P . RRd . De . ME Freyburg 224 0.0863 0.0228 0.2807 0.623 9.99 8 0.27 12.5 0.66 ME Hybrid 506 0.0366 0.0035 0.1494 0.569 36.55 8 <0.001 5.3 Riverhead NY 342 0.4042 0.2258 0.6826 1.068 12.01 9 0.21 58.6 −0.35 NY Hybrid 245 0.0266 0.0130 0.0571 1.238 6.42 4 0.17 3.9 Michigan 250 0.1779 0.0100 1.9172 2.031 18.64 8 0.02 25.8 0.31 MI Hybrid 247 0.1034 0.0061 0.7411 0.393 4.84 6 0.56 15.0 Susceptible 217 0.0069 0.0014 0.0137 1.57 13.14 4 0.01 1.0 Population . Na . LD50b . Lowerc . Upperc . Slope . χ 2 . df . P . RRd . De . ME Freyburg 224 0.0863 0.0228 0.2807 0.623 9.99 8 0.27 12.5 0.66 ME Hybrid 506 0.0366 0.0035 0.1494 0.569 36.55 8 <0.001 5.3 Riverhead NY 342 0.4042 0.2258 0.6826 1.068 12.01 9 0.21 58.6 −0.35 NY Hybrid 245 0.0266 0.0130 0.0571 1.238 6.42 4 0.17 3.9 Michigan 250 0.1779 0.0100 1.9172 2.031 18.64 8 0.02 25.8 0.31 MI Hybrid 247 0.1034 0.0061 0.7411 0.393 4.84 6 0.56 15.0 Susceptible 217 0.0069 0.0014 0.0137 1.57 13.14 4 0.01 1.0 aNumber of second-instar larvae tested. bLD50s are in units of µg/larva. c95% fiducial limits. dLD50 of a given field population/LD50 of the susceptible laboratory line. eDominance as in Stone (1968) ranging from fully recessive (−1) to fully dominant (1). Open in new tab In contrast, higher level resistance from the South Fork of Long Island was much more, perhaps fully, recessive (Table 2). The resistance ratio was 15 times greater than seen in the Riverhead population sampled in 2010. Dominance, D, of −0.73 had confidence limits of −1.02 to −0.43, so not significantly different from fully recessive and significantly less than additive, and also less than −0.35 seen in Riverhead, NY, 2 yr earlier. Table 2. Resistance to spinosad of L. decemlineata from the most resistant population in eastern New York in 2012, a susceptible laboratory colony, and hybrids of between the two Population . Na . LD50b . Lowerc . Upperc . Slope . c2 . df . P . RRd . De . LI resistant 266 1.1406 0.5467 5.0625 0.629 7.03 7 0.43 877.3 −0.73 Hybrids 144 0.0032 0.0038 0.0074 2.4 2.58 8 0.96 2.5 NJ 354 0.0013 0.0016 0.0029 2.05 1.62 5 0.90 1.0 Population . Na . LD50b . Lowerc . Upperc . Slope . c2 . df . P . RRd . De . LI resistant 266 1.1406 0.5467 5.0625 0.629 7.03 7 0.43 877.3 −0.73 Hybrids 144 0.0032 0.0038 0.0074 2.4 2.58 8 0.96 2.5 NJ 354 0.0013 0.0016 0.0029 2.05 1.62 5 0.90 1.0 aNumber of second-instar larvae tested. bLD50s are in units of µg/larva. c95% fiducial limits. dLD50 of a given field population/LD50 of the susceptible laboratory line. eDominance as in Stone (1968) ranging from fully recessive (−1) to fully dominant (1). Open in new tab Table 2. Resistance to spinosad of L. decemlineata from the most resistant population in eastern New York in 2012, a susceptible laboratory colony, and hybrids of between the two Population . Na . LD50b . Lowerc . Upperc . Slope . c2 . df . P . RRd . De . LI resistant 266 1.1406 0.5467 5.0625 0.629 7.03 7 0.43 877.3 −0.73 Hybrids 144 0.0032 0.0038 0.0074 2.4 2.58 8 0.96 2.5 NJ 354 0.0013 0.0016 0.0029 2.05 1.62 5 0.90 1.0 Population . Na . LD50b . Lowerc . Upperc . Slope . c2 . df . P . RRd . De . LI resistant 266 1.1406 0.5467 5.0625 0.629 7.03 7 0.43 877.3 −0.73 Hybrids 144 0.0032 0.0038 0.0074 2.4 2.58 8 0.96 2.5 NJ 354 0.0013 0.0016 0.0029 2.05 1.62 5 0.90 1.0 aNumber of second-instar larvae tested. bLD50s are in units of µg/larva. c95% fiducial limits. dLD50 of a given field population/LD50 of the susceptible laboratory line. eDominance as in Stone (1968) ranging from fully recessive (−1) to fully dominant (1). Open in new tab Discussion Although there was considerable variation between strains in 2010, none of them were significantly different from additive resistance. The most resistant strain—Long Island—was also the most recessive. Two years later, the resistance of the Long Island strain was much more recessive, being significantly different from additive, but not from fully recessive. The fields from which these two sets of resistant beetles were collected are approximately 38 km apart. Highly spinosad-resistant Colorado potato beetles show recessive inheritance of resistance. The three moderately resistant populations sampled in 2010 all had close to additive resistance. Though high-level resistance was identified in 2010 (Schnaars-Uvino 2013), that population was not sampled for this study of mode of inheritance. When that population was examined for this study in 2012, resistance was fully or close to fully recessive. This change in dominance on Long Island suggests that perhaps the spinosad resistance trait was present in 2010 and had spread across the eastern part of the island by 2012. If true, this would theoretically make resistance easier to control, as long as there are costs to high-level resistance because the beetles are trading resistance for some diminution of overall fitness. There is considerable disagreement about the best way to estimate dominance of resistance. Stone (1968) calculated a quantitative estimate of the degree of dominance of the LD50. Roush and McKenzie (1987) however argued that it is difficult to apply estimates of dominance based on laboratory studies to field conditions. Differences may arise due to differing conditions between laboratory and field. An alternative is to assess the relative mortality level at a given pesticide concentration, which is usually referred to as effective dominance (Bourguet et al. 2000). That estimates dominance at a single high dose, in order to more closely simulate actual field conditions in the laboratory and find a single high dose that would kill heterozygotes. This approach assumes that insects in the field are exposed to a single, high dose and that dose is the same as would be applied in the field but that is difficult to achieve. Pesticides can be washed away by rainfall and they break down over time. Spinosad especially breaks down very quickly (Saunders and Bret 1997). Even a plant that takes up pesticide systemically will vary in concentration over the life of that plant. Smaller plants have higher concentrations of pesticide, whereas in older, larger plants, the pesticide is more diffused (Alford and Krupke 2017). In this case, we wanted to show how quantitatively different homozygotes are relative to the heterozygotes, so we calculated the dominance of the LD50. What’s interesting about the results of our 2012 survey is that they show actual dominance of spinosad resistance, not just effective dominance in the field. This suggests that the moderate resistance seen in the first 4 yr of spinosad use on Long Island (Alyokhin et al. 2015) had a different genetic basis than the high-level resistance seen starting in 2010 in the South Fork. This is consistent with the pattern of polygenic, additive, low levels of resistance seen early in the initial use of a new ingredient or in laboratory selection studies of resistance prior to the appearance of novel mutations of large effect (Roush and McKenzie 1987). Dominance modifier genes may also play a role in the pattern of dominance uncovered in this study. Bourguet et al. (1997) found evidence for such modifier genes in organophosphate and carbamate-resistant Culex pipiens, Linnaeus, Diptera: Culicidae. Those genes, they speculated, boosted acetylcholinesterase activity in resistant strains, enough that heterozygotes were able to survive bioassays in the laboratory, and making resistance more dominant. A similar phenomenon could be taking place with these populations of L. decemlineata. Although the exact mechanism of spinosad resistance in L. decemlineata is unknown, around half of the studies to date have identified target site mutations in other species—like organophosphate-resistant C. pipiens—that confer spinosad resistance (Sparks et al. 2012). One reason to think this might not be the case here is that each resistant strain of C. pipiens in the above-mentioned study exhibited identical mortality curves and differed only in dominance (Bourguet et al. 1997). The different strains of L. decemlineata in the present investigation differ in both resistance level and dominance, perhaps indicating that the differences seen here are more likely due to environmental conditions than genetic modifications. Varying levels of dominance of spinosad resistance present challenge the developing effective management strategies. Recessive resistance can be managed with the high-dose refuge strategy that uses high enough doses of pesticide to kill heterozygotes and spatial refuges that allow resistant individuals to develop free from selection pressure and then mix with the resistant population, so long as the resistant individuals are relatively rare (Tabashnik 2008). Resistance in the Long Island strains has declined sharply since this investigation began (Klein 2019). Spinosad failure has been reported from these fields, and its use was discontinued on the South Fork after this investigation (Schnaars-Uvino 2013), creating a temporal refuge for susceptible individuals to migrate onto the farms and mate with the resident individuals. In addition, other active ingredients with different modes of action were deployed. Since resistance on Long Island was recessive, the result would be more heterozygotes that are less resistant to spinosad. Managing dominant resistance is more difficult. One method is to increase the concentration of the insecticide to a level that would kill heterozygotes (Tabashnik et al. 2004). That raises some practical problems though. It is not feasible in all cases to estimate the appropriate concentration to kill heterozygotes and it also poses increased risk to nontarget, potentially beneficial species (Roush and McKenzie 1987). Denholm and Rowland (1992) suggest that denying refuges to insect pests—i.e., not rotating to other types of pesticide and not maintaining untreated fields—may be a more effective strategy to decrease dominance. That prevents resistant individuals from having the opportunity to migrate to an untreated area and mix with susceptible individuals (Preisler et al. 1990). The situation may be more complicated in the case of polygenic resistance. Recent studies provide evidence that Colorado potato beetle resistance to imidacloprid depends on the action of multiple genes, including cuticular proteins, cytochrome P450, monooxygenases, and glutathione synthetases (Clements et al. 2016, Naqqash et al. 2020). The choice of management strategy is ideally based on local resistance and life-history traits. A thorough understanding of those characteristics between geographically isolated populations provides the ability to customize control techniques based on local conditions (Chen et al. 2014). There is often a great deal of variation in resistance, dominance, and fitness between populations of L. decemlineata. Imidacloprid resistance was first documented in the eastern United States in the late 1990s (Olson et al. 2000). Northeastern populations remained susceptible until around 2003 and resistant populations in the Midwest outnumbered susceptible ones only around 2010 (Szendrei et al. 2012). Several studies have documented differences in imidacloprid resistance between different regions of the United States. Chen et al. (2014) found variation between populations in the Northeast, Midwest, and Mid-Atlantic regions. Crossley et al. (2018) found differences in resistance between populations in the Upper Midwest and Pacific Northwest. Huseth et al. (2015) and Crossley et al. (2017) found considerable variation between populations within the Upper Midwest region that might be related to the intensity of farming between different fields. The level of dominance of insecticide resistance is an important factor in determining the types of strategies that are used in controlling insect pests. Dominance can vary between geographically isolated populations and even between interconnected populations. Spinosad resistance was found to be incompletely dominant in Maine and Michigan but incompletely recessive on a large, conventional farm on Long Island. 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Google Scholar Crossref Search ADS PubMed WorldCat © The Author(s) 2020. 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/open_access/funder_policies/chorus/standard_publication_model)
TI - Geographic Variation in Dominance of Spinosad Resistance in Colorado Potato Beetles (Coleoptera: Chrysomelidae)
JF - Journal of Economic Entomology
DO - 10.1093/jee/toaa274
DA - 2021-02-09
UR - https://www.deepdyve.com/lp/oxford-university-press/geographic-variation-in-dominance-of-spinosad-resistance-in-colorado-qjmMyN1VAV
SP - 320
EP - 325
VL - 114
IS - 1
DP - DeepDyve
ER -