Enzyme Activity in Strains of the Sawtoothed Grain Beetle (Coleoptera: Cucujidae) Differentially Resistant to Fenitrothion, Malathion, and Chlorpyrifos-Methyl

Four strains of Oryzaephilus surinamensis (L.) with differing levels of resistance to malathion, fenitrothion, and chlorpyrifos-methyl were assayed for a range of enzymic systems associated with resistance. High resistance to fenitrothion was correlated with high monooxygenase activity; high resistance to chlorpyrifos-methyl was correlated with high esterase activity. No such relationship was apparent with malathion. This information helps explain the complex resistance patterns observed in this species and will aid in decisions regarding choice of insecticides for its control.