Investigation of potential non-target effects to a ladybeetle Propylea japonica in the scenario of RNAi-based pea aphid control

Abstract

Biopesticides based on RNA interference (RNAi) act in a sequence-dependent manner. Homology between target genes in insect pests and orthologs in non-target beneficial insects should therefore be investigated during the design of double-stranded RNA (dsRNA) constructs and by experimental testing to evaluate off-target effects. Here we investigated potential off-target effects against the ladybeetle Propylea japonica (Thunberg) (Coleoptera: Coccinellidae), an important biological control agent, in the context of RNAi-based aphid control. First, we sequenced the full-length P. japonica transcriptome and predicted potential off-target sites at the whole-transcriptome level in the pea aphid Acyrthosiphon pisum (Harris) (Hemiptera: Aphididae) as queries. We found off-target sites in almost every P. japonica genes. Second, we found that first-instar P. japonica larvae were more sensitive to dsRNA exposure than other developmental stages by comparing the silencing efficiency of three indicator genes ( IAP, V-ATP and CHMP-4b). The expression of core siRNA pathway genes after dsRNA treatment confirmed that the response to dsRNA was more robust in first-instar larvae than adults. Finally, we used the A. pisum alpha-actinin gene as a case study to design dsRNA fragments with different degrees of efficacy against P. japonica, confirming that the safety of RNAi approaches can be enhanced by rational dsRNA design.