S-methoprene resistance in the lesser grain borer Rhyzopertha dominica

The lesser grain borer, Rhyzopertha dominica is a serious pest of stored grains. Fumigation and contact insecticides play a major role in managing this pest globally. While insects are developing genetic resistance to chemicals, hormonal analogues such as s-methoprene play a key role in reducing general pest pressure as well managing pest populations that are resistant to fumigants and neurotoxic contact insecticides. However, resistance to s-methoprene has been reported in R. dominica while there are some reports that show a remarkable high levels, recently, questioning the use of this compound and other related analogues in grain protection. The current study attempt to identify possible molecular mechanisms that contribute to resistance to s-methoprene in R. dominica. Transcriptome analysis of resistant and susceptible populations of this pest species identified a set of differentially expressed genes related to cytochrome P450s, indicating their potential role in resistance to s-methoprene. Laboratory bioassays were performed with s-methoprene treated wheat grains in presence and absence of piperonyl butoxide (PBO), a cytochrome P450 inhibitor. Our results indicated that the number of produced progeny decreased in presence of the inhibitor, especially in the resistant strain. In addition, we also identified CYP complement (CYPome) of R. dominica, annotated and analysed phylogenetically, to understand the evolutionary relationships with other species. The information generated in current study suggest that PBO can effectively be used to break resistance to s-methoprene in R. dominica.