RNA interference using double stranded RNAs as molecular biopesticide to regulate the invasive insect pest brown marmorated stink bug (BMSB)

Halyomorpha halys (Stål) (Heteroptera: Pentatomidae), the brown marmorated stink bug (BMSB), an insect native to the Asian continent has flourished as a major invasive insect pest in the United States since its accidental introduction in the Allentown, Pennsylvania area in the late 1990s.  The BMSB is a polyphagous piercing/sucking feeder on over 300 known plant hosts.  It poses a considerable ecological and economic threat of billions of dollars annually to specialty crops, ornamental plants, vegetables, and seed crops.  BMSB has been detected in 42 states in the United States, Canada and Europe, and its damage has been predominantly in the U.S. Mid-Atlantic Region (DE, MD, PA, NJ, VA, and WV).

The aim of this study was to generate molecular biopesticides detrimental to BMSB from in vitro transcribed gene specific double stranded RNAs (dsRNAs) to selectively trigger the RNA interference (RNAi) post-transcriptional sequence specific regulation of gene prevalent in all living things.  In nature, RNAi-mediated gene silencing takes place when target gene RNAs are degraded by sequence-specific dsRNAs into short RNAs, which then activate ribonucleases targeting homologous messenger RNAs thereby leading to their translational blockage.  RNAi technology holds great potential for use in insect control, but the lack of methods for delivery of dsRNA triggers for RNAi into pest insects has been a considerable problem, especially for piercing/sucking insects like BMSB.  Reports of successful delivery of dsRNAs to hemipteran insects have been accomplished only by direct microinjection of the dsRNAs into the insect using a needle.  However, to create practical molecular biopesticides the route of dsRNA entry into insects must be by oral delivery through feeding.  Therefore, we developed a method to deliver selected dsRNAs to BMSBs orally through feeding.  

BMSB-specific genes were selected for RNAi from BMSB transcriptome profiles and dsRNAs transcribed to these specific genes were fed to 4^th instar BMSB nymphs.  Our observations revealed that expression of each specific gene (referred to here as Gene A, Gene B, Gene C, Gene D, and Gene E) was significantly depleted in the insect.  Surprisingly, the expression of Gene E was dramatically diminished, by ≈25 fold compared with the mock control. Highest concentrations of dsRNA for Gene A and Gene B caused death of the test insects fed on the respective dsRNAs approximately 4 days post ingestion.  Currently, classical biological control strategies using natural enemies or predators, as well as novel management tools including pheromone lures for monitoring and trapping, are being used with some success for BMSB.  Newer biologically- and genetically-based control methods employing RNAi-based molecular biopesticides, such as the orally delivered dsRNAs for BMSB developed and described here, have potential to become a new paradigm for insect pest management.