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

Abstract

BACKGROUND: 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. RESULTS: Concentrations required to reach 50% (LC 50 ) and 90% mortality (LC 90 ) 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. CONCLUSIONS: 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.

Identification and risk assessment of spinosad resistance in a California population of Drosophila suzukii

“…). Additional resistance ratios were calculated using susceptible LC 50 values from Van Timmeren et al . as the baseline, and these results indicated much higher levels of resistance, with values ranging from 11.6 to 22.4 for WAT flies and 17.4–32.7 for WAT‐S (Table ).…”

“…Susceptibility of WAT and WOLF populations to spinosad was tested using a glass vial residue bioassay protocol recently developed for D. suzukii . This method was also adopted by research teams throughout the country as part of a nationwide monitoring program that aimed to detect putatively resistant populations for various insecticides that are commonly used in D. suzukii management (Isaacs R, unpublished).…”

“…Following the protocol used in the resistance monitoring survey, we performed mortality assessments after 6 h of exposure for all dose–response trials. However, because moribund flies were commonly observed at this time point during the first round of bioassays, we adopted an additional 8‐h mortality assessment, as suggested by Van Timmeren et al . for all remaining tests (see Table for 8‐h sample sizes).…”

“…RR S = resistance ratio, LC 50 of WOLF, WAT and WAT‐S strains/LC 50 of susceptible Michigan strain; Michigan male LC 50 s: 10 mg kg −1 at 6 h and 7.2 mg kg −1 at 8 h; Michigan female LC 50 s: 16.3 mg kg −1 at 6 h and 13.1 mg kg −1 at 8 h.…”

“…These concerns were heightened based on the findings of a 2017 national resistance monitoring survey in which D. suzukii from the Monterey Bay Region showed elevated levels of survival at the spinosad LC 50 and LC 99x2 concentrations relative to other sites in the USA (Isaacs R, unpublished). The two concentrations used in this survey were generated using susceptible colonies of D. suzukii from untreated Michigan fields and provide a baseline for assessing resistance in field populations . However, elevated survival at these concentrations is not sufficient for confirming resistance; instead, full dose–response analyses are needed to generate and compare lethal concentration values of susceptible and putatively resistant field populations.…”