Susceptibility of Tribolium castaneum to phosphine in China and functions of cytochrome P450s in phosphine resistance

Abstract

Worldwide application of phosphine fumigation has caused the development of resistance especially in Tribolium castaneum during the past 30 years. The understanding of how phosphine is metabolized by insects will benefit the management of phosphine resistance in stored-grain pests. In this study, ten field populations of T. castaneum were collected from different cities in China. Bioassays showed that XD, CD, ZB and GD populations were strongly resistant to phosphine with resistant ratios (RRs) higher than 160, followed by resistant populations QH and HK and four susceptible populations FX, CD, NX and TL. Enzyme activity assays showed that cytochrome P450 activities in resistant populations were higher than susceptible populations and P450 activities were up-regulated in phosphine-resistant T. castaneum after exposure to phosphine. Moreover, CYP345A subfamily members, CYP345A1 and CYP345A2, were significantly overexpressed in resistant populations. After phosphine treatment, the expression levels of CYP345A1 and CYP345A2 were up-regulated. Moreover, RNAi via dsRNA injection was effective to knock down the expression levels of CYP345A1 and CYP345A2 and resulted in an increase of the susceptibility to phosphine in T. castaneum, respectively. Overall, higher P450 enzyme activity and overexpression of CYP345A subfamily genes likely contribute to phosphine resistance in T. castaneum. The results will provide a foundation for developing better strategies to control stored-grain pests.