RNAi efficacy is enhanced by chronic dsRNA feeding in pollen beetle

Abstract

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 αCOP (dsαCOP). In short-term dsαCOP feeding, only the highest concentration resulted in significant reductions in B. aeneus survival; whereas in chronic dsαCOP feeding, all three concentrations resulted in significant mortality. Chronic dsαCOP feeding also resulted in significantly greater mortality compared to short-term feeding of equivalent dsαCOP 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.

Highly Variable Dietary RNAi Sensitivity Among Coleoptera

“… Knorr et al (2018) observed at least 90% adult B. aeneus mortality after 14 days, in all four target gene treatments examined, after dietary exposure to water containing 1 μg dsRNA/μl followed by continuous uptake of dsRNA in artificial diet containing 500 ng/cm 2 . Willow et al (2020 , 2021a , b , c) examined RNAi sensitivity in B. aeneus via multiple field-relevant routes of exposure, and in both adults and larvae. A SIGS approach to achieving RNAi-induced mortality in B. aeneus , via feeding on dsRNA-treated oilseed rape buds and anthers, leads to variable success in achieving a lethal phenotype in this pest species.…”

Anther-Feeding-Induced RNAi in Brassicogethes aeneus Larvae

“…In the present study, significant αCOP silencing at 3 d, in B. aeneus larvae fed dsαCOP at 2.5 µg/µL, substantiates the interpretation that this significant mortality was indeed the result of αCOP silencing. Willow et al (2021) also showed significantly greater mortality in B. aeneus adults chronically fed dsαCOP, compared to the mortality observed in short-term (3 d) treatments. Similar to the effect we observed in the present study regarding B. aeneus larvae fed dsαCOP 2.5 µg/µL-treated anthers, B. aeneus adults fed honey water at 1 and 3 µg dsαCOP/µL showed significant mortality at 6 d and 4 d, respectively (Willow et al, 2020b).…”

“…In a previous experiment comparing short-term-to chronic dsRNA feeding, B. aeneus adults that fed for 3 d on dsαCOP 2.5 µg/µL-treated anthers did not show significantly reduced survival (Willow et al, 2021). A significant reduction in B. aeneus adult survival was observed rather after 8 d of chronic feeding on dsαCOP 2.5 µg/µL-treated anthers, compared to the present study which showed significantly reduced survival at 4 d in larvae fed dsαCOP 2.5 µg/µL-treated anthers for 3 d. Thus, we here observed quicker RNAi-induced mortality in B. aeneus larvae, compared to what has been previously observed in B. aeneus adults that were fed comparable dsαCOP treatments.…”

“…(syn. Meligethes aeneus), via field relevant routes of exposure, including consumption of dsRNA-treated oilseed rape buds (Willow et al, 2020a) and anthers (Willow et al, 2021) as well as dsRNA-treated honey water, representing dsRNA-contaminated nectar (Willow et al, 2020b). The above-mentioned studies were performed on B. aeneus adults, the adult stage being the typical focus of insecticide bioassays regarding this pest species (but see Melander et al, 2003).…”

Lab-to-Field Transition of RNA Spray Applications – How Far Are We?

“…This baseline study provides the first valuable insights on the broad applicability and transferability of RNA sprays over a geographic range in Europe (Mehlhorn et al, 2020). While the accessibility of phyllophagous pests by RNA sprays may seem trivial, a breakthrough was achieved by providing the first laboratory evidence that feeding dsRNA-coated oilseed rape buds to the pollen beetle Brassicogethes aeneus diminishes pollen beetle survival rate (Willow et al, 2021). This study is significant because many pathogens and pests that tremendously impact agriculture infect ears and buds rather than leaves.…”