RNAi efficacy is enhanced by chronic dsRNA feeding in pollen beetle

Double-stranded RNAs (dsRNAs) represent a promising class of biosafe insecticidal compounds. We examined the ability to induce RNA interference (RNAi) in the pollen beetle Brassicogethes aeneus via anther feeding, and compared short-term (3 d) to chronic (17 d) feeding of various concentrations of dsRNA targeting alpha COP (ds alpha COP). In short-term ds alpha COP feeding, only the highest concentration resulted in significant reductions in B. aeneus survival; whereas in chronic ds alpha COP feeding, all three concentrations resulted in significant mortality. Chronic ds alpha COP feeding also resulted in significantly greater mortality compared to short-term feeding of equivalent ds alpha COP concentrations. Our results have implications for the economics and development of dsRNA spray approaches for managing crop pests, in that multiple lower-concentration dsRNA spray treatments across crop growth stages may result in greater pest management efficacy, compared to single treatments using higher dsRNA concentrations. Furthermore, our results highlight the need for research into the development of RNAi cultivars for oilseed rape protection, given the enhanced RNAi efficacy resulting from chronic, compared to short-term, dsRNA feeding in B. aeneus. Jonathan Willow et al. use ds alpha COP-treated anthers to examine RNAi efficacy against pollen beetle, a major pest of oilseed rape. The authors found that chronic feeding resulted in significantly greater mortality compared to short-term feeding; and significant silencing of alpha COP was detected only in beetles chronically exposed to ds alpha COP