A little help from my friend: Virus infection reduces susceptibility of beet leafhoppers to neonicotinoid insecticides

Sugar beets are grown across the western United States for their lucrative taproot and are an economically important crop generating 1.16 billion dollars in 2021. However, production is threatened by the beet curly top virus (BCTV), a viral pathogen that severely reduces yield. The virus is exclusively transmitted by the beet leafhopper, Circulifer tenellus. Current management options for BCTV rely on neonicotinoid seed treatments and pyrethroid foliar sprays. However, there are reports of neonicotinoid resistance in numerous insect pests and this insecticide group may have harmful effects on non-target insects. Hence, the goal of this research is to examine susceptibility of beet leafhoppers to three different application rates (2x, 1x, 0.1x) of insecticides and determine their ability to lower virus transmission. We hypothesize that applying insecticide at a higher label rate will result in an increased mortality of beet leafhoppers, and therefore reduced virus transmission. At the 1x rate, neonicotinoids were more effective than pyrethroids, yielding 100% mortality of BCTV-infected and non-infected insects. However, at the 0.1x rate BCTV-infected leafhoppers had a higher survival rate than non-infected insects. This result was observed in only the neonicotinoid trials and not the pyrethroid trials. Although experiments are ongoing, confirming this potential insecticide resistance in BCTV-infected insects would be a key piece of information to aid in tracking the epidemiology of BCTV and make predictions about leafhopper populations. With this knowledge, farmers would be able to adjust their management strategies to achieve more sustainable and profitable sugar beet production practices.