Carboxyesterase degradation of malathion in vitro by susceptible and resistant strains of Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae)

Malathion monoacid was found to be the major metabolite of malathion produced in vitro by homogenates of susceptible and resistant Tribolium castaneum. Slightly increased production of this metabolite was detected in a malathion specific resistant strain. In all strains, monoacid formation was inhibited by triphenyl phosphate. Partial purification of the enzymes responsible failed to indicate a significant increase in enzyme levels in the resistant strain.