Comparison of the oxidant damage induced by phosphine and the uptake and tracheal exchange of ³²P-radiolabelled phosphine in the susceptible and resistant strains of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae)

Abstract

The activity of antioxidant enzymes and the effects of phosphine on them were compared in a susceptible and two resistant strains of Rhyzopertha dominica (F.). Phosphine treatment lowered the activity of catalase and peroxidase and raised the activity of superoxide dismutase and the content of lipid peroxides in the susceptible insects. The generation of toxic oxyradical species appeared to be taking place in insects as a consequence of the interaction of phosphine with the mitochondrial respiration. Compared to the extent of oxidant damage in the susceptible insects, phosphine treatment caused only minor effects in a laboratory-selected strain while it produced no significant effects in a highly resistant field strain, even when treated at higher doses. The dietary administration of buthionine sulphoximine (BSO) lowered the content of glutathione in the resistant insects but caused no appreciable change in the susceptible strain. There were no appreciable effects on the susceptibility of BSO-treated strains to phosphine or on the uptake of ³²P when treated with ³²P-radiolabelled phosphine. In a “pulse-chase” style experiment, the resistant insects showed a much lower uptake of ³²P and a significantly greater exchange of gaseous [³²P]PH₃ compared to the susceptible strain. The mechanisms of insect resistance to phosphine are discussed in the light of these results.