Hafiz Azhar Ali Khan
Methomyl resistance is a documented problem in Musca domestica field strains worldwide, including Pakistan, where the insecticide is commonly used. To address this, a methomyl-resistant near-isogenic line (Meth-R) was created specifically to determine its resistance inheritance mode and cross-resistance profile. Analysis of reciprocal F1 and F1' crosses demonstrated autosomal inheritance of methomyl resistance in the Meth-R strain, as evidenced by similar median lethal dose (LD50) values and the absence of sex linkage or maternal effects. Resistance expression was incompletely dominant, with dominance values of 0.7 (F1) and 0.6 (F1'). Significant deviations between observed and expected mortality in self-bred (F2 and F2') and backcross (BC1-BC4) progenies (chi-square analyses) indicate resistance is likely controlled by multiple genes. The Meth-R strain showed no cross-resistance to alpha-cypermethrin, fluralaner, pirimiphos-methyl, or clothianidin. Additionally, observing significant synergism of methomyl with both piperonyl butoxide (PBO; oxidase inhibitor) and S,S,S-tributyl phosphorotrithioate (DEF; esterase inhibitor) implicates metabolic detoxification as a key mechanism of methomyl resistance. The Meth-R strain exhibits methomyl resistance inherited as an autosomal, incompletely dominant trait under polygenic control. Although there was cross-resistance in the Meth-SEL strain to alpha-cypermethrin, fluralaner, pirimiphos-methyl, and clothianidin versus the lab susceptible strain, selection with methomyl did not increase the level of cross-resistance. These results offer a foundation for combating methomyl resistance.