TY - JOUR
AU1 - Rendon,, Dalila
AU2 - Walton, Vaughn, M
AB - Abstract Overhead sprinkler compared to drip irrigation in cropping systems can result in increased relative humidity (RH) and decreased temperature within the plant canopy. Such conditions may also result in a more favorable microclimate for pests. Drosophila suzukii Matsumura is an invasive agricultural pest of berries in America and Europe. Drosophila suzukii is susceptible to high temperatures and low RH, thus its survival may be affected by different irrigation methods. We tested how drip and overhead sprinkler irrigation in blueberries influenced temperature and RH. Furthermore, we determined how these environmental factors affected adult emergence rates from larvae within fruit or pupae outside of fruit. RH was higher in overhead sprinkler compared to drip irrigation treatments, but there was no difference in temperatures. Although there were no differences in fly emergence from larvae between irrigation treatments, more flies emerged from pupae in overhead sprinkler compared to drip irrigation treatments. This is likely because larvae developing inside fruit are protected from desiccation, while pupae were exposed to lower RH. Regardless of irrigation method, temperatures remained above 30°C for longer periods and RH was lower above as opposed to below the mulch. Fewer D. suzukii larvae and pupae consequently survived above the mulch than below the mulch. When assessing natural infestation, we found similar numbers of D. suzukii flies emerging from blueberries collected on drip and sprinkler rows. Irrigation management can be coupled with other cultural control methods that ensure that pupae remain exposed on low RH surfaces, where they are more likely to succumb to desiccation. spotted-wing drosophila, integrated pest management, water Agricultural practices implemented to improve crop production may also help improve pest management. The amount of water delivered by different irrigation methods can have profound effects on both pest populations and crop damage (Perfect 1986). Some irrigation methods may also create environments with high humidity and moderate temperature fluctuations in the plant canopy, providing a favorable microclimate for pests to thrive. As such, it is important to consider the impacts on integrated pest management when designing an irrigation system to optimize plant production. The effect of irrigation on insect pest populations has been examined in multiple crops. In some cases, excess water or additional irrigation can be detrimental to insects. For example, irrigation can delay development and affect survival of bollworm Helicoverpa pupae in the soil (Yu et al. 2008). Furthermore, drip-irrigated coffee plants can have fewer leaf miners compared to non-irrigated plants (Assis et al. 2012). In a contrasting scenario, increased irrigation can increase pest population and damage. For instance, in vineyards, higher volumes of drip irrigation can lead to increased late-season leafhopper populations (Daane and Williams 2003). In some crops, a single irrigation method can affect some insects positively, and others negatively. For example, reduced field irrigation can decrease the abundance of chewing insects in cotton, but increase the abundance of other sucking insects (Murrell 2017). Irrigation can also indirectly affect pest populations; for instance, reduced flooding in rice can increase natural enemy populations, leading to greater biocontrol (Murrell 2017). Previous research on irrigation and insect management has focused mostly on the amount of water delivered (e.g., Irvin et al. 2016, Rousselin et al. 2016), but few compare different irrigation methods. In one study in pear trees, overtree irrigation did not alter the number of fruit infested with codling moth (Cydia pomonella), pear psylla, and spider mite populations compared to trees irrigated with an undertree sprinkler system (Westigard et al. 1979). Although determining the optimal irrigation method is an essential step for crop production, there is little knowledge on how different irrigation systems affect pest populations. Drosophila suzukii Matsumura (spotted-wing drosophila) is an invasive agricultural pest of berries in America and Europe (Walsh et al. 2011, Dos Santos et al. 2017). Females possess a serrated ovipositor that enables them to lay eggs inside ripening fruit, leading to crop loss (Lee et al. 2016). In berries, D. suzukii management relies on insecticide sprays (Van Timmeren and Isaacs 2013, Diepenbrock et al. 2016), but economic and environmental unsustainability issues of chemical control make it necessary to seek complementary integrated pest management strategies. Additional management strategies may rely on agricultural practices that can modify the crop microenvironment, making it less favorable for D. suzukii survival and development. Various studies have investigated how relative humidity (RH) affects D. suzukii in laboratory and field conditions. Tochen et al. (2016) reported that D. suzukii reproduction is higher at RH greater than 80% in laboratory conditions, and that higher ambient RH correlates to higher trap captures in the field. In blackberries, fruit infestations can be higher in the inner canopy, where RH is also higher (Diepenbrock and Burrack 2016). Although RH may influence the microenvironment preference of D. suzukii, flies have been reported to be similarly active during and after irrigation events (Van Timmeren et al. 2017). Furthermore, flight performance in D. suzukii does not seem to be affected by RH (Wong et al. 2018). It is thus unclear how different irrigation methods can modify conditions such as temperature or RH, and whether any changes in the abiotic conditions can affect D. suzukii survival and development in the field. In blueberries (Vaccinium corymbosum L.; Ericales: Ericaceae), different irrigation methods have mostly been studied for fruit production and pathogen suppression (i.e., susceptibility to fungal disease or transmission of bacteria). In different regions, irrigation methods are tailored to mitigate locally relevant berry production issues; for instance, overhead sprinkler irrigation is often used to prevent frost damage in the Northeastern United States (Rodriguez-Saona, personal communication), or in an attempt to lower berry temperature and increase firmness in other regions (Yang 2018). In drip irrigation systems in blueberries, the spacing of the lines can influence the incidence of root rot (Yeo et al. 2017). Plants receiving water by drip irrigation systems produce higher berry yields with less water usage (Bryla 2010, Bryla et al. 2011), but also have higher incidence of root rot compared to plants on sprinkler irrigation (Bryla and Linderman 2007). The effect of different irrigation methods on D. suzukii development in blueberries is currently unknown. This study aims to investigate the influence of overhead sprinkler and drip irrigation in blueberries on 1) ground temperatures and RH, 2) D. suzukii immature (larval and pupal) survival, and 3) natural infestation in berries. Methods Field Site and Irrigation Regimes Irrigation trials were conducted in a blueberry (cv. Elliott) plot at the Lewis-Brown Farm at Oregon State University, Corvallis, OR (44°33′13′′N 123°13′07′′W), during the growing seasons of 2016 and 2017 (Fig. 1). Blueberry bushes were planted in 2004 on a raised bed containing approximately 5 cm of Douglas-fir (Pseudotsuga mensienzii; The Bark Place, Corvallis, OR) sawdust mulch. The blueberry plot was 24 rows wide by 72 bushes long, bushes were spaced approximately 0.76 m apart within rows and 3.05 m between rows. The canopy size was 150–160 cm tall, and 100–130 cm wide. The whole plot was divided into randomized complete block irrigation configurations in each row (Fig. 1); eight rows were selected for each treatment, such that each row was considered an experimental unit (N = 8). Irrigation treatments included drip and overhead sprinklers. Overhead sprinkler 90° angle nozzles (Rain Bird Corp., Glendora, CA, model 1802QDS) were mounted above the plant beds, delivering water at a rate of up to 2.8 liters/min. Drip tubing (Netafim, Fresno, CA, UniRam 570) was positioned under the sawdust mulch approximately 0.2 m from the base of the plants, and had 2 liter/h pressure-compensating emitters every 0.45 m. Drip irrigation was scheduled to run three to seven times a week, and sprinkler irrigation two to three times per week, for a 2.5-h period starting at 2000 h for sprinklers and 0400 h for drip for every irrigation event. The number of irrigation events and volume of water delivered by overhead and drip irrigation was adjusted to optimize fruit production according to crop growth stage, and weekly evapotranspiration (ET) rates and rainfall, assuming a 50% water loss from overhead sprinklers (Bryla et al. 2011). As a result, each treatment received a different amount of water depending on the replication date, and we acknowledge this as a confounding factor. Irrigation trials were replicated during the growing season according to fruit ripening on 20 May 2016 (‘Early 2016’), 1 Sep 2016 (‘Late 2016’), 1 June 2017 (‘Early 2017’), and 27 July 2017 (‘Mid 2017’). During 2016, blueberries were sprayed with a rotation of malathion (5 July and 4 August; 1.98 pints active ingredient [ai]/acre, 2,342 ml ai/Ha) and zeta-cypermethrin (21 July; 0.025 ai/acre, 28.32 g ai/Ha), but no insecticides were applied during trials. No insecticides were applied during 2017. Details of ET, rainfall, ambient temperature, and irrigation volumes for each trial date are summarized in Table 1. Table 1. ET, rainfall, and ambient temperature values in blueberry plots during trial dates in Corvallis, OR, during 2016 and 2017 Trial dates Prior week total ET (mm) Prior week total rainfall (mm) Prior week net ET (mm) Average max. air temperature (°C) 20–26 May 2016 19.55 5.84 13.71 16.11 1–7 Sep 2016 21.08 5.08 16.0 21.70 31 May–6 June 2017 28.95 0.0 28.95 27.30 20–26 July 2017 44.70 3.30 41.4 31.05 Trial dates Prior week total ET (mm) Prior week total rainfall (mm) Prior week net ET (mm) Average max. air temperature (°C) 20–26 May 2016 19.55 5.84 13.71 16.11 1–7 Sep 2016 21.08 5.08 16.0 21.70 31 May–6 June 2017 28.95 0.0 28.95 27.30 20–26 July 2017 44.70 3.30 41.4 31.05 Water volumes applied during the trial week replenish net ET from the previous week, compensating a 50% water loss in overhead sprinkler plots, according to crop growth stage (Bryla et al. 2011). Open in new tab Table 1. ET, rainfall, and ambient temperature values in blueberry plots during trial dates in Corvallis, OR, during 2016 and 2017 Trial dates Prior week total ET (mm) Prior week total rainfall (mm) Prior week net ET (mm) Average max. air temperature (°C) 20–26 May 2016 19.55 5.84 13.71 16.11 1–7 Sep 2016 21.08 5.08 16.0 21.70 31 May–6 June 2017 28.95 0.0 28.95 27.30 20–26 July 2017 44.70 3.30 41.4 31.05 Trial dates Prior week total ET (mm) Prior week total rainfall (mm) Prior week net ET (mm) Average max. air temperature (°C) 20–26 May 2016 19.55 5.84 13.71 16.11 1–7 Sep 2016 21.08 5.08 16.0 21.70 31 May–6 June 2017 28.95 0.0 28.95 27.30 20–26 July 2017 44.70 3.30 41.4 31.05 Water volumes applied during the trial week replenish net ET from the previous week, compensating a 50% water loss in overhead sprinkler plots, according to crop growth stage (Bryla et al. 2011). Open in new tab Fig. 1. Open in new tabDownload slide Blueberry planting (cv. Elliot and Duke) irrigation map. Each ‘x’ represents one blueberry bush. Shaded areas were not used for experiments. A total of eight row sections (clear areas, each an experimental unit, N = 8) were used in trials; location of Drosophila suzukii bags and dataloggers within each section was randomized for each trial date. Fig. 1. Open in new tabDownload slide Blueberry planting (cv. Elliot and Duke) irrigation map. Each ‘x’ represents one blueberry bush. Shaded areas were not used for experiments. A total of eight row sections (clear areas, each an experimental unit, N = 8) were used in trials; location of Drosophila suzukii bags and dataloggers within each section was randomized for each trial date. Irrigation and Abiotic Factors We explored the following variables as predictors of temperature and %RH: 1) irrigation method (drip or overhead sprinkler), 2) location in relation to mulch (above or buried 1–3 cm below the sawdust mulch), and 3) berry growth season (early, mid, or late season). Temperature and RH were measured every 20 min in the blueberry rows using external dataloggers (HOBO U23 Pro v2 Temperature/%RH; Onset Computer Corp., Bourne, MA) for 7-d periods. For each irrigation method, dataloggers were placed directly above and buried 1–3 cm below the sawdust mulch (one datalogger in a separate row replicate, N = 3–4 for each treatment combination). From each treatment, we measured the total time (in minutes) above 30°C (D. suzukii developmental arrest threshold, Ryan et al. 2016), and mean RH for the 7-d trials when artificially infested blueberries and pupae cages were exposed in the field (see Artificial Infestation and D. suzukii Survival). To determine the effect of each variable on temperature and RH, a general linear model was performed using irrigation method, mulch location, and season as fixed effects. Variables were transformed using a Box–Cox power transformation to meet assumptions of normality and heteroscedasticity (Box and Cox 1964). All data analyses henceforth were performed in RStudio (RStudio Team 2016); data were organized using the package ‘dplyr’ (Wickham and Francois 2016), the transformations and general linear model analyses were performed using the packages ‘MASS’ (Venables and Ripley 2002) and ‘car’ (Fox and Weisberg 2011), and all graphs were produced using the package ‘ggplot2’ (Wickham 2009). Artificial Infestation and D. suzukii Survival We explored the following variables as predictors of D. suzukii survival: 1) irrigation method (drip or overhead sprinkler), 2) D. suzukii location in relation to mulch (lying above or buried 1–3 cm below the sawdust mulch), and 3) berry growth season (early, mid, or late season). Commercially sourced California organic blueberries were artificially infested by exposing the berries to mature D. suzukii females from laboratory colonies and allowing them to freely oviposit for 24–48 h. This was done by placing berries arranged in petri dishes inside either colony cages or inside 473 ml plastic vented containers with 10 mature (at least 7 d old) females. After exposure, each blueberry fruit was inspected under a dissecting microscope to count the number of eggs laid. In order to avoid intraspecies larval competition, only blueberries containing fewer than eight eggs were used during the experimental procedure (Bezerra Da Silva, unpublished data). Twenty (±2) infested blueberries containing a total of 50 ± 3 eggs were then distributed in a white organza bag (5.5 × 10.5 × 1.5 cm; Gifts International Inc., Bloomington, CA). Pupal survival outside of fruit was determined by attaching 20 D. suzukii pupae (1–2 d after pupation) inside wire rectangular cages (5 × 5 × 1 cm, referred to as ‘pupal cages’) using double-sided clear tape. All pupae were covered with a moist paper towel to avoid desiccation, and the clear tape was covered with sawdust to prevent emerging flies from getting entangled. Pupal cages were then placed inside white organza bags in order to protect them from parasitism or predation during each trial period. Due to low colony numbers, pupae were not tested in late 2016. Organza bags containing infested blueberries or pupal cages were placed in blueberry rows 1–2 d following blueberry infestation or pupal cage setup. The organza bags with infested blueberries or pupae were placed in split-plot treatments, in sections with drip or overhead sprinkler, and either on top of or buried 1–3 cm below the sawdust mulch. Additional control blueberries and pupal cages were kept in laboratory conditions for the duration of the trial. Bags containing infested blueberries and pupal cages were left in the field for 7 d, and no pesticides were applied in the blueberry plot during this period. In some rows, we placed more than one bag with infested blueberries or pupal cages depending on availability; we then took the average of all bags in a single row treatment, and used this value as a single replicate, such that sample size per treatment was N = 8 (number of plot rows used in the trials, Fig. 1). After this period of field exposure, the bags were removed from the field and placed in controlled laboratory conditions (22.5 ± 2.5°C, 50–70 % RH) for an additional 3–4 wk. Bags were checked three times a week, and newly emerged flies were removed and counted, until no more flies emerged. The total number of emerged D suzukii flies in each bag was recorded to determine the proportion of emerged flies (compared to the total number of eggs in blueberries or pupae originally in each bag) as an outcome variable. To determine the effect of each variable on D. suzukii survival, we performed a beta regression using irrigation method, ground location, and season as fixed effects. Beta regressions are appropriate for outcome variables bound between 0 and 1 (in this case, proportion of flies emerged from total eggs) and are not subject to assumptions of heteroscedasticity (Ferrari and Cribari-Neto 2004). Beta regressions were performed using the RStudio package ‘Betareg’ (Cribari-Neto and Zeileis 2010). Natural Infestations of D. suzukii We assessed weekly natural infestation in blueberries during July and August 2017 in the same treatment rows as above. Ripe berries were collected from the ground in the sections with drip and sprinkler irrigation (N = 8 rows for each date). Collected berries were kept in ventilated plastic containers in controlled laboratory conditions (22.5 ± 2.5°C, 50–70 % RH) for an additional 3–4 wk. Newly emerged flies were counted and removed from containers, and the total number of emerged D. suzukii flies in each container was recorded. Because the number of berries collected varied by date, we divided the number of D. suzukii by the total number of berries collected to obtain an estimate of D. suzukii per berry. To determine the effect of irrigation method on number of D. suzukii per berry, an analysis of variance on log-transformed data was performed using irrigation method (drip or overhead sprinkler) as a fixed effect, and date as a blocking factor. Results The relationships between irrigation method, mulch location, and season on temperature (time above 30°C), RH, and D. suzukii survival are described in Table 2 and Supp Table S1 (online only). Irrigation method (drip or overhead sprinkler) did not affect temperature (time above 30°C) or flies emerged from infested blueberries, but drip irrigation rows had significantly lower RH and lower D. suzukii emergence from pupae compared to overhead sprinkle irrigation rows (Figs. 2a and b and 3a and b). Above the mulch, temperatures remained above 30°C for longer periods, RH was lower, and D. suzukii emergence from both infested blueberries and pupae was lower, compared to below the mulch (Figs. 2a and b and 3a and b). Table 2. Regression parameters for the effects of irrigation method, mulch location, and season on temperature (total time above 30°C, in minutes), mean RH, and D. suzukii survival from artificially infested blueberries or pupal cages in Corvallis, OR, during 2016 and 2017 Outcome variables Temperature (time above 30°C) RH (%) Drosophila suzukii emergence (infested blueberries) Drosophila suzukii emergence (pupal cages) Fixed effects df F P df F P df χ2 P df χ2 P Irrigation method 1, 51 1.45 0.23 1, 51 34.61 <0.01 1 0.15 0.69 1 6.86 <0.01 Mulch location 1, 51 11.26 <0.01 1, 51 52.43 <0.01 1 70.36 <0.01 1 28.02 <0.01 Season 3, 51 6.62 <0.01 3, 51 26.05 <0.01 3 4.20 0.24 2 6.89 0.03 Outcome variables Temperature (time above 30°C) RH (%) Drosophila suzukii emergence (infested blueberries) Drosophila suzukii emergence (pupal cages) Fixed effects df F P df F P df χ2 P df χ2 P Irrigation method 1, 51 1.45 0.23 1, 51 34.61 <0.01 1 0.15 0.69 1 6.86 <0.01 Mulch location 1, 51 11.26 <0.01 1, 51 52.43 <0.01 1 70.36 <0.01 1 28.02 <0.01 Season 3, 51 6.62 <0.01 3, 51 26.05 <0.01 3 4.20 0.24 2 6.89 0.03 Effects on temperature and RH were estimated using a general linear model with Box–Cox lambda transformations, and effects on D. suzukii survival were calculated using a beta regression. Open in new tab Table 2. Regression parameters for the effects of irrigation method, mulch location, and season on temperature (total time above 30°C, in minutes), mean RH, and D. suzukii survival from artificially infested blueberries or pupal cages in Corvallis, OR, during 2016 and 2017 Outcome variables Temperature (time above 30°C) RH (%) Drosophila suzukii emergence (infested blueberries) Drosophila suzukii emergence (pupal cages) Fixed effects df F P df F P df χ2 P df χ2 P Irrigation method 1, 51 1.45 0.23 1, 51 34.61 <0.01 1 0.15 0.69 1 6.86 <0.01 Mulch location 1, 51 11.26 <0.01 1, 51 52.43 <0.01 1 70.36 <0.01 1 28.02 <0.01 Season 3, 51 6.62 <0.01 3, 51 26.05 <0.01 3 4.20 0.24 2 6.89 0.03 Outcome variables Temperature (time above 30°C) RH (%) Drosophila suzukii emergence (infested blueberries) Drosophila suzukii emergence (pupal cages) Fixed effects df F P df F P df χ2 P df χ2 P Irrigation method 1, 51 1.45 0.23 1, 51 34.61 <0.01 1 0.15 0.69 1 6.86 <0.01 Mulch location 1, 51 11.26 <0.01 1, 51 52.43 <0.01 1 70.36 <0.01 1 28.02 <0.01 Season 3, 51 6.62 <0.01 3, 51 26.05 <0.01 3 4.20 0.24 2 6.89 0.03 Effects on temperature and RH were estimated using a general linear model with Box–Cox lambda transformations, and effects on D. suzukii survival were calculated using a beta regression. Open in new tab Fig. 2. Open in new tabDownload slide (a) Time (total minutes) above 30°C and (b) relative humidity (%, mean ± SE) above and below the sawdust mulch on two irrigation systems (drip and overhead sprinkler) in an ‘Elliot’ blueberry plot in Corvallis, OR during 2016 and 2017. Bars with same letters in each season are not significantly different (Tukey HSD, adjusted alpha for multiple pairwise comparisons). Fig. 2. Open in new tabDownload slide (a) Time (total minutes) above 30°C and (b) relative humidity (%, mean ± SE) above and below the sawdust mulch on two irrigation systems (drip and overhead sprinkler) in an ‘Elliot’ blueberry plot in Corvallis, OR during 2016 and 2017. Bars with same letters in each season are not significantly different (Tukey HSD, adjusted alpha for multiple pairwise comparisons). Fig. 3. Open in new tabDownload slide Proportion of Drosophila suzukii flies emerged (mean ± SE) from (a) artificially infested blueberries and (b) pupal cages placed above and below the sawdust mulch on two irrigation systems (drip and overhead sprinkler) in an ‘Elliot’ blueberry plot in Corvallis, OR during 2016 and 2017. Bars with same letters in each season are not significantly different (Tukey HSD, adjusted alpha for multiple pairwise comparisons). Fig. 3. Open in new tabDownload slide Proportion of Drosophila suzukii flies emerged (mean ± SE) from (a) artificially infested blueberries and (b) pupal cages placed above and below the sawdust mulch on two irrigation systems (drip and overhead sprinkler) in an ‘Elliot’ blueberry plot in Corvallis, OR during 2016 and 2017. Bars with same letters in each season are not significantly different (Tukey HSD, adjusted alpha for multiple pairwise comparisons). Temperatures, RH, and D. suzukii emergence were similar in both early and late 2016. Compared to early 2016, temperatures remained above 30°C for longer and RH was lower in late 2017, yet there were no significant differences in D. suzukii emergence from infested blueberries and pupae between the two dates. Compared to early 2016, in early 2017, RH was lower, and D. suzukii survival from pupae was higher (Supp Table S1 [online only]). Irrigation method (drip or overhead sprinkler) did not have an effect on number of flies emerged from berries collected on sawdust mulch (df = 1, 95, F = 1.37, P = 0.24). On average, drip rows had 0.36 ± 1.1 and sprinkler rows had 0.59 ± 1.55 (mean ± SD) D. suzukii emerging per berry. Discussion This study is the first to provide insight on the role of irrigation and its impact on survival of larval and pupal life stages of D. suzukii under commercial-standard field conditions. Overall, the RH was higher in overhead sprinkler rows compared to drip rows, but there was no difference in temperature (total time above 30°C). Significantly fewer D. suzukii emerged from pupae on drip rows compared to overhead sprinkler. No differences between irrigation methods were, however, observed when looking at D. suzukii larvae in artificially infested blueberries. These observations were probably due to the fact that, while larvae develop within fruit and are protected from desiccation, pupae were exposed to dry air. The lower RH recorded in drip irrigation rows thus likely contributed to the lower rates of survival of exposed pupae, but had little effect on larvae developing in blueberries. Both temperature and RH are known to affect pupal survival, but low RH can exacerbate the lethal effects of continuous exposure to high temperatures (Enriquez and Colinet 2017). If D. suzukii larvae within infested blueberries had been allowed to pupate outside of fruit in field conditions, we might have observed an effect survival due to irrigation on D. suzukii emergence from blueberries. Temperatures remained above 30°C and RH was lower above the mulch compared to below the mulch regardless of irrigation method. We also observed fewer D. suzukii larvae and pupae surviving above the mulch compared to below the mulch. These results suggest that differences in survival are likely attributable to the observed environmental conditions. These results are consistent with those found in a previous study on the effect of mulching on D. suzukii survival in multiple regions across the Unites States, where D. suzukii survival was also consistently lower above the mulch than below the mulch (Rendon et al., unpublished data). Larvae are reported to leave the fruit to pupate underground (Woltz and Lee 2017), where there is a more favorable microenvironment for development. In the closely related Drosophila melanogaster, it was shown that pupation choice is affected by moisture, and that larvae prefer to leave their growth media to pupate when damp substrates are available (Godoy Herrera et al. 1989). Future studies should address how irrigation method and ambient RH can modify pupation location behavior. Berries collected from drip-irrigated rows had similar numbers of D. suzukii emerging as adults per berry compared to berries from sprinkler rows. Drip-irrigated blueberries are often softer (Bryla 2010), which could lead to higher susceptibility to oviposition (Lee et al. 2016). However, the similarities between drip and sprinkler irrigation show that risk of increased D. suzukii infestation is unlikely to be a concern for growers wanting to adopt drip irrigation systems. In drier or hotter areas, the differences between drip and sprinkler irrigation on D. suzukii infestation might be more pronounced. As such, the effect of irrigation methods on D. suzukii survival in other regions and berry crops warrant further study. Because sprinkler systems distribute water over a broader area, RH can thus remain higher over a larger volume of air within the irrigation zone. In contrast, drip irrigation deposits water only over a reduced surface, meaning that RH will remain high only in close vicinity of the drip pores. The blueberry canopies in these trials were more than 1 m wide. This means that even berries located in the outer canopy were likely within the high RH microenvironment provided by overhead sprinkler irrigation. Any larvae exiting from fruit further away from plant stems in sprinkler irrigation areas would likely experience more favorable pupation conditions than larvae exiting in drip rows. As explained above, irrigation showed no effect on natural infestation of D. suzukii, but the fruit that we collected had larvae within when they were removed to the field and taken to favorable laboratory conditions to continue their development. From this study, it is thus not possible to know what would have happened to larvae exiting the fruit in the field in drip or overhead sprinkler rows. Any changes in D. suzukii larval presence in blueberries might be due to female activity and oviposition preference in drip or sprinkler rows, arrested larval development in either irrigation method, or a combination of these factors. Because in this study we looked only at fly emergence (as evidence of successful development), but did not count eggs present in berries (as evidence of oviposition), we do not report these interactive effects. Some studies have explored the role of ambient RH on adult activity only; for example, Van Timmeren et al. (2017) found that in certain instances, adult flies are less abundant in blueberry rows with overhead sprinklers during irrigation events than in rows without irrigation, but this reduction was small and inconsistent. Even though Wong et al. (2018) found that RH does not affect flight performance in D. suzukii, Tochen et al. (2016) found that in blueberry fields, more D. suzukii adults were trapped in areas with higher RH. Other studies looked only at the effect of RH on field oviposition. In blackberries, oviposition and RH are higher in the inner portion of the canopy, but it is unknown whether these trends are due to female preference or egg mortality (Diepenbrock and Burrack 2016). There is thus currently no evidence that the oviposition activity of D. suzukii adults is affected by overhead sprinkler irrigation events. One possibility is that females might reduce their oviposition activity in sprinkler rows, but the associated higher RH is more favorable for larval development. Future studies are needed to elucidate the relationships between irrigation, RH, D. suzukii female oviposition behavior, and immature development. In addition to the effects on crop microclimate, drip and overhead sprinkler irrigation may also interfere with chemical controls. Rain events or overhead irrigation can reduce the effectiveness of some insecticides against D. suzukii (Van Timmeren and Isaacs 2013, Gautam et al. 2016). While the effect of irrigation method on insecticide efficacy was not evaluated in this study, it is important to consider the scenarios in which overhead sprinklers may reduce insecticide persistence in berry crops. In summary, drip irrigation rows provided a less favorable environment for the development of D. suzukii pupae compared to sprinkler irrigation. Because larvae within fruit were not significantly affected by irrigation method, it is possible that drip irrigation can be coupled with other cultural control methods to ensure that pupae remain exposed on the surface of drip rows, where they are more likely to succumb to desiccation. Other cultural methods may include the use of physical barriers, such as plastic mats, where larvae are unable to dig through to pupate underground (Rendon et al., unpublished data). This study illustrates how manipulating RH in crop microenvironments can be used as a useful strategy in conjunction with other integrated pest management methods to reduce D. suzukii population pressure in berry crops. Acknowledgments We would like to thank Dr. David Bryla at the Horticultural Crops Research Unit (United States Department of Agriculture – Agricultural Research Service [USDA-ARS]) in Corvallis, OR, for access to blueberry research plots. Scott Orr and Fan-Hsuan Yang provided assistance with irrigation records and plot management. Gabriella Boyer, Jessica Buser, and Dr. Jana Lee assisted in setting up trials, and all the members of the Walton lab counted eggs in infested blueberries. This project was funded by a United States Department of Agriculture National Institute for Food and Agriculture (USDA-NIFA) award, #2015-51181-24252 and USDA-NIFA Organic Agriculture Research and Extension Initiative #2014-51300-22238. References Cited Assis , G. A. , F. A. Assis , M. S. Scalco , F. J. T. Parolin , I. Fidelis , J. C. Moraes , and R. J. Guimaraes . 2012 . Leaf miner incidence in coffee plants under different drip irrigation regimes and planting densities . Pesqui. Agropecu. Bras . 47 : 157 – 162 . Google Scholar Crossref Search ADS WorldCat Box , G. E. P. , and D. R. Cox . 1964 . An analysis of transformations (with discussion) . J. R. Stat. Soc. Ser. B Stat. Soc . 26 : 211 – 252 . WorldCat Bryla , D. R . 2010 . Irrigation management methods to manipulate fruit quality in blueberry . HortScience 45 : S49 – S49 . Google Scholar Crossref Search ADS WorldCat Bryla , D. R. , and R. G. Linderman . 2007 . Implications of irrigation method and amount of water application on Phytophthora and Pythium infection and severity of root rot in highbush blueberry . HortScience 42 : 1463 – 1467 . Google Scholar Crossref Search ADS WorldCat Bryla , D. R. , J. L. Gartung , and B. C. Strik . 2011 . Evaluation of irrigation methods for highbush blueberry-I. growth and water requirements of young plants . HortScience 46 : 95 – 101 . Google Scholar Crossref Search ADS WorldCat Cribari-Neto , F. , and A. Zeileis . 2010 . Beta regression in R . J. Stat. Softw . 34 : 1 – 24 . (https://cran.r-project.org/web/packages/betareg/betareg.pdf) (accessed 26 June 2018). Google Scholar Crossref Search ADS WorldCat Daane , K. M. , and L. E. Williams . 2003 . Manipulating vineyard irrigation amounts to reduce insect pest damage . Ecol. Appl . 13 : 1650 – 1666 . Google Scholar Crossref Search ADS WorldCat Diepenbrock , L. M. , and H. J. Burrack . 2016 . Variation of within-crop microhabitat use by Drosophila suzukii (Diptera: Drosophilidae) in blackberry . J. Appl. Entomol . 141 : 1 – 7 . Google Scholar Crossref Search ADS WorldCat Diepenbrock , L. M. , D. O. Rosensteel , J. A. Hardin , A. A. Sial , and H. J. Burrack . 2016 . Season-long programs for control of Drosophila suzukii in southeastern blueberries . Crop. Prot . 84 : 171 . Google Scholar Crossref Search ADS WorldCat Dos Santos , L. A. , M. F. Mendes , A. P. Krüger , M. L. Blauth , M. S. Gottschalk , and F. R. Garcia . 2017 . Global potential distribution of Drosophila suzukii (Diptera, Drosophilidae) . PLoS ONE 12 : e0174318 . Google Scholar Crossref Search ADS PubMed WorldCat Enriquez , T. , and H. Colinet . 2017 . Basal tolerance to heat and cold exposure of the spotted wing drosophila, Drosophila suzukii . PeerJ 5: e3112 . WorldCat Ferrari , S. L. P. , and F. Cribari-Neto . 2004 . Beta regression for modeling rates and proportions . J. Appl. Stat . 31 : 799 – 815 . Google Scholar Crossref Search ADS WorldCat Fox , J. , and S. Weisberg . 2011 . An R companion to applied regression , 2nd ed. Thousand Oaks, CA: Sage . Google Preview WorldCat COPAC Gautam , B. K. , B. A. Little , M. D. Taylor , J. L. Jacobs , W. E. Lovett , R. M. Holland , and A. A. Sial . 2016 . Effect of simulated rainfall on the effectiveness of insecticides against spotted wing drosophila in blueberries . Crop Prot . 81 : 122 – 128 . Google Scholar Crossref Search ADS WorldCat Godoy Herrera , R. , L. Cifuentes , M. F. D. Dearcaya , M. Fernandez , M. Fuentes , I. Reyes , and C. Valderrama . 1989 . The behavior of Drosophila melanogaster larvae during pupation . Anim. Behav . 37 : 820 – 829 . Google Scholar Crossref Search ADS WorldCat Irvin , N. A. , A. Bistline-East , and M. S. Hoddle . 2016 . The effect of an irrigated buckwheat cover crop on grape vine productivity, and beneficial insect and grape pest abundance in southern California . Biol. Control 93 : 72 – 83 . Google Scholar Crossref Search ADS WorldCat Lee , J. C. , D. T. Dalton , K. A. Swoboda-Bhattarai , D. J. Bruck , H. J. Burrack , B. C. Strik , J. M. Woltz , and V. M. Walton . 2016 . Characterization and manipulation of fruit susceptibility to Drosophila suzukii . J. Pest Sci . 89 : 771 – 780 . Google Scholar Crossref Search ADS WorldCat Murrell , E. G . 2017 . Can agricultural practices that mitigate or improve crop resilience to climate change also manage crop pests ? Curr. Opin. Insect Sci . 23 : 81 – 88 . Google Scholar Crossref Search ADS PubMed WorldCat Perfect , T. J . 1986 . Irrigation as a factor influencing the management of agricultural pests . Philos. Trans. A Math. Phys. Eng. Sci . 316 : 347 – 354 . Google Scholar Crossref Search ADS WorldCat Rousselin , A. , M. H. Sauge , M. O. Jordan , G. Vercambre , F. Lescourret , and D. Bevacqua . 2016 . Nitrogen and water supplies affect peach tree-green peach aphid interactions: the key role played by vegetative growth . Agric. For. Entomol . 18 : 367 – 375 . Google Scholar Crossref Search ADS WorldCat RStudio Team . 2016 . RStudio: integrated development for R . RStudio Inc. , Boston, MA . (http://www.rstudio.com/) (accessed 17 May 2017). Google Preview WorldCat COPAC Ryan , G. D. , L. Emiljanowicz , F. Wilkinson , M. Kornya , and J. A. Newman . 2016 . Thermal tolerances of the spotted-wing Drosophila Drosophila suzukii (Diptera: Drosophilidae) . J. Econ. Entomol . 109 : 746 – 752 . Google Scholar Crossref Search ADS PubMed WorldCat Tochen , S. , J. M. Woltz , D. T. Dalton , J. C. Lee , N. G. Wiman , and V. M. Walton . 2016 . Humidity affects populations of Drosophila suzukii (Diptera: Drosophilidae) in blueberry . J. Appl. Entomol . 140 : 47 – 57 . Google Scholar Crossref Search ADS WorldCat Van Timmeren , S. , and R. Isaacs . 2013 . Control of spotted wing drosophila, Drosophila suzukii, by specific insecticides and by conventional and organic crop protection programs . Crop. Prot . 54 : 126 – 133 . Google Scholar Crossref Search ADS WorldCat Van Timmeren , S. , L. Horejsi , S. Larson , K. Spink , P. Fanning , and R. Isaacs . 2017 . Diurnal activity of Drosophila suzukii (Diptera: Drosophilidae) in highbush blueberry and behavioral response to irrigation and application of insecticides . Environ. Entomol . 46 : 1106 – 1114 . Google Scholar Crossref Search ADS PubMed WorldCat Venables , W. N. , and B. D. Ripley . 2002 . Modern applied statistics with S , 4th ed. Springer , New York . (https://cran.r-project.org/web/packages/MASS/MASS.pdf) (accessed 26 June 2018). Google Preview WorldCat COPAC Walsh , D. B. , M. P. Bolda , R. E. Goodhue , A. J. Dreves , J. Lee , D. J. Bruck , V. M. Walton , S. D. O’Neal , and F. G. Zalom . 2011 . Drosophila suzukii (Diptera: Drosophilidae): invasive pest of ripening soft fruit expanding its geographic range and damage potential . Integr. Pest. Manag . 2 : G1 – G7 . Google Scholar Crossref Search ADS WorldCat Westigard , P. H. , P. B. Lombard , and R. B. Allen . 1979 . Effects of overtree irrigation on density and damage of pear pests . J. Econ. Entomol . 72 : 839 – 840 . Google Scholar Crossref Search ADS WorldCat Wickham , H . 2009 . ggplot2: elegant graphics for data analysis . Springer-Verlag , New York . Google Preview WorldCat COPAC Wickham , H. , and R. Francois . 2016 . dplyr: a grammar of data manipulation. R package version 0.5.0 . (https://CRAN.R-project.org/package=dplyr) (accessed 17 May 2017). Woltz , J. M. , and J. C. Lee . 2017 . Pupation behavior and larval and pupal biocontrol of Drosophila suzukii in the field . Biol. Control 110 : 62 – 69 . Google Scholar Crossref Search ADS WorldCat Wong , J. S. , A. C. Cave , D. M. Lightle , W. F. Mahaffee , S. E. Naranjo , N. G. Wiman , J. M. Woltz , and J. C. Lee . 2018 . Drosophila suzukii flight performance reduced by starvation but not affected by humidity . J. Pest. Sci . 91 : 1269 – 1278 . Google Scholar Crossref Search ADS WorldCat Yang , F. H . 2018 . Predictions and practices for reducing heat damage in northern highbush blueberry (Vaccinium corymbosum L.) . Ph.D. dissertation, Oregon State University, Corvallis, OR. COPAC Yeo , J. R. , J. E. Weiland , D. M. Sullivan , and D. R. Bryla . 2017 . Nonchemical, cultural management strategies to suppress Phytophthora root rot in northern highbush blueberry . HortScience 52 : 725 – 731 . Google Scholar Crossref Search ADS WorldCat Yu , F. L. , G. Wu , T. J. Liu , B. P. Zhai , and F. J. Chen . 2008 . Effects of irrigation on the performance of cotton bollworm, Helicoverpa armigera (Hubner) during different pupal stages . Int. J. Pest. Manag . 54 : 137 – 142 . Google Scholar Crossref Search ADS WorldCat © 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. 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 - Drip and Overhead Sprinkler Irrigation in Blueberry as Cultural Control for Drosophila suzukii (Diptera: Drosophilidae) in Northwestern United States
JF - Journal of Economic Entomology
DO - 10.1093/jee/toy395
DA - 2019-03-21
UR - https://www.deepdyve.com/lp/oxford-university-press/drip-and-overhead-sprinkler-irrigation-in-blueberry-as-cultural-00RoSoby6T
SP - 745
VL - 112
IS - 2
DP - DeepDyve
ER -