RNAi Targeting Chitin synthase Genes Specifically Affects Larval Performance in Tuta absoluta

An RNA interference (RNAi)-based management strategy has a great potential for control of the tomato leafminer Tuta absoluta, a microlepidoptera pest damaging a broad range of Solanaceae hosts. Nevertheless, whether RNAi efficiency of the target genes is affected by dsRNA reachability and mRNA levels remains to be established in T. absoluta. Two chitin synthase genes, TaChSA and TaChSB, were highly expressed in ectodermally-derived cells and midgut respectively, facilitating to test dsRNA reachability using oral delivery. According to the 2^{- ΔCT} value, TaChSA average level was much higher than that of TaChSB, allowing us to compare the mRNA levels on RNAi effectiveness. We found that ingestion of bacterially-expressed dsChSA or dsChSB for 24 h identically decreased the target mRNA levels in whole body, and in the head, epidermis, foregut and hindgut. Feeding dsChSA affected larval growth and leaf mining, caused 19.7% larval lethality and 31.6% non-emerged adults. Moreover, RNAi against TaChSA damaged rectum integrity, decreased cuticle thickness, and thinned tracheae. By contrast, ingesting dsChSB decreased larval weight, led to 3.8% larval lethality and 43.2% of resulting pupae failing to emerge. Taken together, dsChSA and dsChSB might be systemically transported, and exerted a strong RNAi efficiency irrespective of target mRNA levels. Our results indicate a possible application of bacterially-expressed dsChSA and dsChSB in the field to protect growing crops against T. absoluta.