Insecticide residue longevity for on-site screening of Drosophila suzukii (Matsumura) resistance.

Preventative application of insecticides reduces marketable yield losses caused by Drosophila suzukii females that selectively lay eggs into ripe and ripening fruits. However, repeated applications of insecticides increase the risk of resistance development. It is therefore critical to test field-collected flies on-site to assess the level of sensitivity of D. suzukii to insecticides to monitor resistance, before it becomes a widespread issue. This requires that insecticide-treated vials be readily available to conduct bioassays. Thus, bioassays were conducted using malathion-, methomyl-, zeta-cypermethrin-, phosmet-, spinetoram- and spinosad-treated scintillation vials at 1 to 28 days after treatment to assess how residue age affects insecticide toxicity in scintillation vials. The impact of temperature on residue longevity was also assessed. Insecticide-treated vials stored for 28 days provided reliable estimates of susceptibility of D. suzukii to some of the tested insecticides. The toxicity of malathion remained consistently high throughout the experiment followed by methomyl. However, toxicities of zeta-cypermethrin, phosmet were variable whereas those of the spinosyns declined relatively quickly. Overall, storage temperature did not affect the residual toxicity of most of the tested insecticides except zeta-cypermethrin. These findings suggest that the toxicity of insecticide residues in treated vials remains active for ≤28 d for malathion and ≤21 and 28 days in methomyl-treated vials stored at 4 °C in Georgia and Michigan, respectively. However, the toxicities of spinosad, zeta-cypermethrin and phosmet were less consistent. Hence, vials treated with these insecticides should be freshly made to be effective for screening D. suzukii field populations for resistance. © 2020 Society of Chemical Industry.

Disi JO ，Van Timmeren S ，Gress B ，Zalom F ，Isaacs R ，Sial A ... -  《-》

Baseline susceptibility of spotted wing Drosophila (Drosophila suzukii) to four key insecticide classes.

The invasive drosophilid pest, Drosophila suzukii Matsumura, is affecting berry production in most fruit-producing regions of the world. Chemical control is the dominant management approach, creating concern for insecticide resistance in this pest. We compared the insecticide susceptibility of D. suzukii populations collected from conventional, organic or insecticide-free blueberry sites. The sensitivity of D. suzukii to malathion and spinetoram declined slightly across the 3 years of monitoring, whereas it was more consistent for methomyl and zeta-cypermethrin. The sensitivity of D. suzukii to all four insecticides (LC50 and LC90 values) did not differ significantly among the blueberry fields using different management practices. The baseline sensitivity of D. suzukii has been characterized, allowing future comparisons if field failures of chemical control are reported. The concentration achieving high control indicates that effective levels of control can still be achieved with field rates of these four insecticides. However, declining susceptibility of some populations of D. suzukii to some key insecticides highlights the need for resistance monitoring. © 2017 Society of Chemical Industry.

Van Timmeren S ，Mota-Sanchez D ，Wise JC ，Isaacs R ... -  《-》

Development of a rapid assessment method for detecting insecticide resistance in spotted wing Drosophila (Drosophila suzukii Matsumura).

Spotted wing Drosophila is an invasive pest of fruit crops in most production regions globally, and insecticides are commonly used for its control. The biology of this pest combined with repeated pesticide exposure increases the risk of resistance to insecticides. We tested malathion, methomyl, spinetoram, spinosad, and zeta-cypermethrin against multiple colonies from each state using a contact bioassay method to determine diagnostic doses for assessment of insecticide susceptibility in this species. These were used to test populations collected in Michigan and Georgia, USA. Concentrations required to reach 50% (LC50 ) and 90% mortality (LC90 ) were calculated for the tested populations, and male mortality consistently occurred at lower concentrations than female mortality. Fly mortality did not vary significantly among populations collected from unmanaged, organic, and conventional fields. Similar results were found using the diagnostic concentrations applied to glass jars. Using this method, samples of D. suzukii that are freshly caught or reared from fruit can be tested within 1 day for their mortality in response to discriminating doses of five key insecticides. This method can be used to inform proactive resistance management strategies within integrated pest management programs. © 2019 Society of Chemical Industry.

Van Timmeren S ，Sial AA ，Lanka SK ，Spaulding NR ，Isaacs R ... -  《-》

Canopy spray deposition and related mortality impacts of commonly used insecticides on Drosophila suzukii Matsumura (Diptera: Drosophilidae) populations in blueberry.

Insecticide applications in blueberry production systems play a crucial role in the control of Drosophila suzukii populations. Here, quantitative spray deposition patterns were obtained under replicated field experiments in blueberry during two field seasons with three sprayers, i.e. cannon, electrostatic, and air-blast. Seven insecticides were tested (at 6 hours using a Potter spray tower) to determine the mortality data for adult D. suzukii. Spray deposition and mortality data for adult D. suzukii were used to create model simulations for insect populations. Model simulations included field deposition rates of sprayers and insecticide mortality as factors. Simulations were applied in different combinations with five applications over a 6-week period. Relative deposition rates for the cannon sprayer were elevated in the upper zones of the canopy, whereas for the air-blast sprayer, deposition was greater in the bottom zones. Electrostatic spray deposition was relatively uniform within the six canopy zones. Clear trends in D. suzukii laboratory mortality were found with lowest to highest mortality recorded for phosmet, spinetoram, spinosad, malathion, cyantraniliprole, zeta-cypermethrin, and methomyl respectively. Maximum D. suzukii population impacts, as shown by model outputs, were observed with air-blast sprayers together with zeta-cypermethrin. The electrostatic sprayer had the least variable canopy deposition among the three types of spray equipment, and the air-blast sprayer had the highest overall deposition rates. This study provides new hypotheses that can be used for field verification with these spray technologies and insecticides as key factors. © 2019 Society of Chemical Industry.

Mermer S ，Pfab F ，Hoheisel GA ，Bahlol HY ，Khot L ，Dalton DT ，Brewer LJ ，Rossi Stacconi MV ，Zhang C ，Xue L ，Walton VM ... -  《-》

Monitoring of Spotted-Wing Drosophila (Diptera: Drosophilidae) Resistance Status Using a RAPID Method for Assessing Insecticide Sensitivity Across the United States.

Drosophila suzukii (Matsumura) has spread rapidly, challenging berry and cherry crop production due to its ability to lay eggs into ripening fruit. To prevent infestation by this pest, insecticides are applied during fruit ripening and harvest. We field-tested the Rapid Assessment Protocol for IDentification of resistance in D. suzukii (RAPID) on seventy-eight populations collected across eight U.S. states in 2017 and 2018. Exposure to LC50 rates of malathion, methomyl, spinetoram, spinosad, and zeta-cypermethrin led to average female fly mortality of 25.0% in 2017, and after adjusting concentrations the average was 39.9% in 2018. Using LC99 × 2 discriminating concentrations in 2017 and LC90 × 8 rates in 2018, average female mortalities were 93.3% and 98.5%, respectively, indicating high overall susceptibility. However, using these high concentrations we found 32.0% of assays with survival of some female flies in 2017 and 27.8% in 2018. The adjustment in discriminating dose from 2017 to 2018 also reduced the proportion of assays with <90% survival from 17.6 to 2.9%. Populations with low mortality when exposed to spinosad were identified using this assay, triggering more detailed follow-up bioassays that identified resistant populations collected in California coastal region berry crops. Widespread evaluations of this method and subsequent validation in California, Michigan, and Georgia in 2019-2021 show that it provides a quick and low-cost method to identify populations of D. suzukii that warrant more detailed testing. Our results also provide evidence that important insecticide classes remain effective in most U.S. regions of fruit production.

Isaacs R ，Van Timmeren S ，Gress BE ，Zalom FG ，Ganjisaffar F ，Hamby KA ，Lewis MT ，Liburd OE ，Sarkar N ，Rodriguez-Saona C ，Holdcraft R ，Burrack HJ ，Toennisson A ，Drummond F ，Spaulding N ，Lanka S ，Sial A ... -  《-》