Improving RNAi in the Brown Marmorated Stink Bug: Identification of target genes and reference genes for RT-qPCR

The brown marmorated stink bug (BMSB) is native to Asia and recently invaded the USA. RNA interference (RNAi) is a gene silencing mechanism in which the introduction of double-stranded RNA (dsRNA) inhibits gene function by degrading target mRNA. In dsRNA stability assays, the dsRNases present in the hemolymph and salivary gland secretions of BMSB showed lower activity than those in the hemolymph of Heliothis virescens. We evaluated six housekeeping genes (18S rRNA, EF1-alpha, Actin, Ubiquitin, 60S RP and beta-Tubulin) across dsRNA treatments (injection and feeding) in nymphs and adults of BMSB and identified 18S rRNA and 60S RP as the best genes to use as a reference in reverse-transcriptase quantitative PCR (RT-qPCR). Homologs of 13 genes that were shown to function as effective RNAi targets in other insects were identified and evaluated by injecting dsRNA targeting these homologs into BMSB adults. Five out of 13 dsRNAs tested caused more than 70% mortality by seven days after injection of dsRNA. Feeding dsRNA targeting five of these genes (IAP, ATPase, SNF7, GPCR, and PPI) to nymphs caused more than 70% mortality by three of the five dsRNAs tested. These data suggest that feeding dsRNA causes target gene knockdown and mortality in BMSB.