Cytochrome P450-mediated detoxification is one of the most important mechanisms involved in insecticide resistance. High levels of inheritable resistance to phosphine in Tribolium castaneum have been detected. There is a paucity of reports on the molecular mechanism, especially on the role of P450-mediated detoxification, in phosphine resistance of stored product insect pests. A high-level phosphine resistant strain of T. castaneum was screened (resistance factor = 724). PBO synergistic ratios of resistant strains were low (1.77-3.81x). But P450 reductase and cytochrome b5 contents in resistant strains were significantly higher than that of a susceptible strain at 10d, 20d larval and adult (3-4 d of age) stages (P<0.05). The concentrations of P450 reductase and cytochrome b5 were positively correlated with LC50. P450 associated genes CYP4Q4 and CYP4Q7 were overexpressed in the midgut of resistance strains, while CYP similar gene was overexpressed in the fat body of resistant strains (P<0.01).Oxidative metabolism could be involved in phosphine resistance of T. castaneum as high levels of P450 reductase and b5 were detected in resistant strains compared to a susceptible strain. Furthermore, qPCR revealed that P450 associated genes, CYP4Q7, CYP4Q4 and CYP, were up-regulated in the phosphine resistant strains. The study provides the first direct evidence that cytochrome P450 monooxgenases and the over-expression of its related genes are one of metabolic mechanism responsible for phosphine resistance in T.castaneum.
