Author(s): Adriano E Pereira, Newton P Carneiro and Blair D Siegfried
Corn rootworms (CRW) are the most important corn pests in the U.S. Corn Belt. Damage is caused by larval feeding on the plant roots. RNAi has been studied in CRW and has proven to be effective for the management of this insect with effects on both larval and adult stages. The objective of this study was to determine comparative susceptibility of adult and larva of Southern Corn Rootworm (SCR) and Western Corn Rootworm (WCR) to two different lethal RNAi target genes (vacuolar (v)-ATPase-A and Snf7). Adults and larvae were exposed to dsRNAs overlaid on artificial diet five times every other day. WCR larval susceptibility to vATPase-A was approximately 4-fold more tolerant than SCR, but were similar for Snf7 (2.6 ng/cm2 for both species). For adults, LC50s were generally higher for vATPase-A dsRNA relative to larvae with a 20-fold higher LC50 for WCR (SCR=33.3 ng/cm2; WCR=657.3 ng/cm2) relative to Snf7 dsRNAs (SCR=13.2 ng/cm2; WCR=60.2 ng/cm2). Gene silencing was also evaluated in adults and larvae exposed to the LC50 dsRNAs, and gene knockdown ranged from 48% up to 83% in adults fed for eight days in dsRNA, and from 55% to 89% in larvae fed for 24, 48 and 72 h, compared to control treatments. This is the first study to report LC50 values for dsRNA in WCR and SCR adults. The results indicate that both larvae and adults of both species were affected by vATPase-A and Snf7 dsRNAs suggesting that RNAi for the management of CRW should be considered for both stages.