Targeting the proteasome subunit PSMB5 by RNA interference induces proteasome dysfunction and mortality in the Colorado potato beetle (Leptinotarsa decemlineata)

The Colorado potato beetle (CPB, Leptinotarsa decemlineata) is a devastating super-pest of potato crops in the northern hemisphere. Chemical control methods are expensive, harmful to non-target species, and inefficient because CPB populations can rapidly evolve resistance to multiple classes of insecticides. Double-stranded RNA (dsRNA) provides an opportunity for the sustainable and targeted control of CPB by RNA interference (RNAi). A dsRNA active ingredient (ledprona, marketed as Calantha^®) targeting proteasome subunit β5 (PSMB5) achieves the efficient suppression of PSMB5 gene expression and protein synthesis, causing CPB mortality and protecting crop plants in the laboratory and field. To understand the mode of action of ledprona in more detail, expression levels of other proteasome subunit genes and proteins and correspondingly the accumulation of ubiquitinated proteins were measured in ledprona-treated CPB larvae. This study confirms the strong downregulation of PSMB5 mRNA and PSMB5 protein, as well as the systemic upregulation of other proteasome transcripts and the accumulation of cell waste in the form of ubiquitin-labeled degrons that correlate with larval mortality. This comprehensive characterization of ledprona's mode of action expands our previous knowledge of the only sprayable dsRNA pesticide with regulatory registration in the United States and may facilitate future efforts to control CPB.