MULTIPLE MECHANISMS OF PERMETHRIN RESISTANCE IN THE RED FLOUR BEETLE, Tribolium castaneum Herbst
Permethrin resistance in the red flour beetle (Tribolium castaneum Herbst) was characterized using permethrin-selected (R-per1) strain. In the absence of selection pressure, permethrin resistance was stable for 8 (ca. 8 months) generations and then showed a partial decrease in degree of resistance. The resistance was in a stable level in the succeeding months suggesting two types of resistance mechanism. The KT values obtained by 50 topical application of permethrin exhibited a 2.0 fold knockdown resistance (kdr) against larvae of R-per1 as compared to the susceptible strain. The shortened knockdown time as a result of pretreatment with the metabolic inhibitors PBO and DEF confirmed the presence of kdr factor in the permethrin resistant strain. The cytochrome P450 content as estimated by the CO-binding difference spectrum was 2.2 times larger in adult and 2.7 times larger in larva of permethrin-resistant strain, indicating the participation of monooxygenase system as part of the mechanism of resistance. The third mechanism is the participation of esterases as exhibited by an increased activity in the presence of α- and β-naphthyl acetates as substrates, implying a relationship between permethrin resistance and degradation by esterases. The implication of such findings was discussed in relation to the current use of grain protectants in managing resistant stored grain insect pests.
Key words: permethrin, pyrethroid resistance, resistance mechanisms, stability of resistance, red flour beetle
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