Biochemistry of malathion resistance in a strain of Cimex lectularius resistant to organophosphorus compounds.

The penetration of (14)C-labelled malathion was found to be similar in two bedbug strains, of which one was susceptible and the other moderately resistant to a range of organophosphorus insecticides. The latter strain was especially resistant to malathion and fenchlorphos, but was not resistant to organophosphates or (significantly) to organochlorine insecticides. There was no difference in acetylcholinesterase activity or sensitivity, or in total esterase activity (using 1- or 2-naphthyl acetates as substrates). In vitro experiments on malathion metabolism showed about 17% greater degradation in the resistant strain, demethyl malathion and malathion diacid being the main products.