Biochemical Properties Characterizing the Development of Tolerance to Malathion in Ceratitis capitata Wiedemann (Diptera: Tephritidae)

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Abstract
Selection pressure with malathion for 18 generations resulted in a 2- or 3-fold tolerance of adult females of Ceratitis capitata Wiedemann to this insecticide. Male flies showed no increase in tolerance over the same period of selection. Tolerance to malathion in female flies was associated with higher carboxyesterase activity toward p-nitrophenyl acetate and with a lower Ki value for the inhibition of head acetylcholinesterase by malaoxon. No such relationship could be demonstrated with glutathione S-transferase activity using l-chloro-2,4-dinitrobenzene as substrate. In agreement with their lack of increase in tolerance to malathion selection pressure, male flies showed no increase in either of the above enzyme activities.