Resistance developments in Estonia’s population of pollen beetles (Brassicogethes aeneus)

A total of 111 local pollen beetle populations were collected from both winter and spring oilseed rape fields, in the main oilseed growing regions of Estonia between 2015−2019. The objective was to analyse the insecticide-susceptibility of the pollen beetle population (in the form of Brassicogethes aeneus). The pollen beetle samples were tested for sensitivity to lambda-cyhalothrin, thiacloprid, and chlorpyrifos. The efficacy of the tested insecticides varied considerably by region. We observed a clear decrease in susceptibility to lambda-cyhalothrin and thiacloprid, but sensitivity to chlorpyrifos remained stable throughout the period between 2015 and 2019. Amongst the tested samples in that period, a total of 3% were classified as susceptible to lambda-cyhalothrin, 18% as moderately resistant, 70% as resistant, and 7% as highly resistant. In the case of thiacloprid, 21% of the samples were highly susceptible to the insecticide, 39% were susceptible, and 41% had reduced levels of susceptibility to the insecticide. The information which was presented tended to confirm the ongoing evolution of insecticide resistance in the B. aeneus population in Estonia, while also highlighting the importance of data-based decisions when optimising insecticide resistance management in the field.