LAUSR

Abstract Susceptibility of common pollen beetle (Brassicogethes aeneus Fabricius) to four insecticides was monitored at 14 locations in the Czech Republic during 2013–2017 on oilseed rape. Seventy local pollen beetle populations were tested for resistance to lambda-cyhalothrin, etofenprox, chlorpyrifos-ethyl, and thiacloprid. Resistance to lambda-cyhalothrin and etofenprox was determined with the recommended rates of 7.5 g a.i. ha−1 and 40 g a.i. ha−1, respectively. Resistance increased significantly over time only for lambda-cyhalothrin. Chlorpyrifos-ethyl at the recommended rate of 187.5 g a.i. ha−1 exceeded by 4 times the mean 90% lethal dose (LD90) value of 44.4 g a.i. ha−1, and mortality was 100% in all years. Thiacloprid had widely dispersed LD50 and LD90 values, as did lambda-cyhalothrin and etofenprox. Thiacloprid's recommended rate of 72 g a.i. ha−1 was substantially higher than mean LD90 values. Several subpopulations with reduced susceptibility to thiacloprid were, however, found in this study. No cross-resistance among lambda-cyhalothrin, etofenprox, chlorpyrifos, and thiacloprid was determined.