Monitoring Onion Thrips (Thysanoptera: Thripidae) Susceptibility to Spinetoram in New York Onion Fields

Onion thrips (Thrips tabaci Lindeman) is a severe pest of onion (Allium cepa L.). Their management relies on frequent applications of foliar insecticides, including spinetoram (Radiant (R) SC), which has a novel mode of action and is effective at controlling large populations. However, despite being widely used for the past 10 yr, susceptibility to spinetoram has not been evaluated formally in New York state, where nearly 3,000 hectares of onion are planted annually. Over 2 yr (2017-2018), the susceptibility of onion thrips to spinetoram was assessed from populations collected in commercial onion fields in New York. LC(50)s for adults were generated from feeding assays and ranged from 2.07 to 5.08 ppm, but grower reports indicate that onion thrips populations continue to be susceptible to spinetoram. Moreover, both regional and temporal variations in susceptibility were similar among these populations based on survival at individual concentrations tested, despite significant differences in LC(50)s. These results suggest some genetic heterogeneity among onion thrips populations and serve as a valuable reference for the continued monitoring of onion thrips susceptibility to spinetoram, contributing to ongoing efforts to manage insecticide resistance in this system.