Development of RNA interference tools for functional genomic assays and control strategies of Frankliniella occidentalis

The western flower thrips, Frankliniella occidentalis Pergande, is an economically important pest that belongs to the insect order Thysanoptera. This insect causes direct and indirect damage to hundreds of plant species through feeding and transmitting tospoviruses, respectively. Currently, there are no methods to study gene function in thrips, which are necessary to dissect the role of specific genes in thrips-tospovirus interactions. The goal of this work was to develop RNA interference (RNAi) tools to conduct functional genomic assays and evaluate their utility for control strategies of F. occidentalis. Using a microinjection system, we directly delivered double-stranded RNA (dsRNA) against the vATPase-B gene of this insect pest. Gene expression analysis using real-time quantitative PCR showed that there was a significant reduction of the vATPase-B transcript in adult female thrips injected with the corresponding dsRNA compared to those injected with GFP dsRNA at 2 and 3 days post-injection (dpi). This transcript reduction resulted in two observable phenotypes, increased mortality and reduced fertility. Survivorship began to decrease significantly at 6 dpi compared to the negative control, which continued until the end of the bioassay. Adult female thrips injected with vATPase-B dsRNA produced significantly less offspring during 14 dpi compared to the negative control. Thus, RNAi is a functional cellular process in F. occidentalis that can be exploited to ascertain the function of thrips genes in their interaction with tospoviruses. To our knowledge, this represents the first report of RNAi in any thrips species and shows potential to be translated into applied control strategies.