Development of RNAi Methods for the Mormon Cricket, Anabrus simplex (Orthoptera: Tettigoniidae)

SIMPLE SUMMARY: Mormon crickets (Anabrus simplex) are native to the United States and can become devastating rangeland pests. These insects can form migratory bands numbering in the millions, which can traverse the western U.S., damaging agricultural crops, invading urban areas, and producing hazardous slicks on roadways. Current methods of managing these insects involve targeted applications of non-specific chemical insecticides, which can potentially have negative effects on the environment. In this study, we took the first steps toward developing RNA interference (RNAi) methods, a type of gene silencing technique that has potential for pest management, for Mormon crickets as a potential alternative to traditional broad-spectrum insecticides. We first generated genomic resources to identify several candidate genes and developed double-stranded RNA (dsRNA) for these genes, which could be injected into the insect to induce gene silencing. We performed RNAi experiments to characterize gene knockdown efficiencies and demonstrated that it is possible to elicit RNAi responses in the Mormon cricket by injection, but knockdown efficiencies varied according to the target genes and tissue types. We conclude that RNAi silencing is possible in Mormon cricket, but more work needs to be done before it can be effectively used as a population management method. ABSTRACT: Mormon crickets are a major rangeland pest in the western United States and are currently managed by targeted applications of non-specific chemical insecticides, which can potentially have negative effects on the environment. In this study, we took the first steps toward developing RNAi methods for Mormon crickets as a potential alternative to traditional broad-spectrum insecticides. To design an effective RNAi-based insecticide, we first generated a de novo transcriptome for the Mormon cricket and developed dsRNAs that could silence the expression of seven housekeeping genes. We then characterized the RNAi efficiencies and time-course of knockdown using these dsRNAs, and assessed their ability to induce mortality. We have demonstrated that it is possible to elicit RNAi responses in the Mormon cricket by injection, but knockdown efficiencies and the time course of RNAi response varied according to target genes and tissue types. We also show that one of the reasons for the poor knockdown efficiencies could be the presence of dsRNA-degrading enzymes in the hemolymph. RNAi silencing is possible in Mormon cricket, but more work needs to be done before it can be effectively used as a population management method.