Evaluation of dsRNA produced in E. coli for controlling Japanese beetle

The Japanese beetle (Popillia japonica) is a highly polyphagous invasive pest that causes significant economic damage to field crops, ornamentals, and turf. Traditionally, large amounts of broad-spectrum chemical insecticides have been used to target both adults and larvae, but with limited success mainly due to resistance. RNA interference (RNAi) might provide an alternative method for species-specific control by silencing essential survival genes with double-stranded RNAs (dsRNAs). Injecting dsRNA targeting the actin and ATPCL genes reduced their expression and caused death in Japanese beetle adults. However, orally delivered dsActin did not induce knockdown of the target gene or mortality. Exposure of dsRNA to lumen contents, followed by electrophoresis, showed that dsRNases present in the lumen digest dsRNA, suggesting that degradation of orally delivered dsRNA may contribute to its ineffectiveness. In contrast, dsActin produced in Escherichia coli and fed to adult beetles caused target gene knockdown, reduced feeding on rose leaves, and increased mortality. When heat-killed bacteria were sprayed onto okra plants in covered field plots, a similar effect was observed; the plants were better protected by dsActin than by control dsGFP. These results from laboratory assays and preliminary field trials suggest that using heat-killed bacteria that produce dsRNA targeting essential genes in Japanese beetles could offer a cost-effective strategy for its control.