Background: The cabbage moth, Mamestra brassicae, is a polyphagous pest that attacks several crops. Here, the sublethal and lethal effects of chlorantraniliprole and indoxacarb were investigated on the developmental stages, detoxification enzymes, reproductive activity, calling behavior, peripheral physiology, and pheromone titer of M. brasssicae. Methods: To assess pesticide effects, the second instar larvae were maintained for 24 h on a semi-artificial diet containing insecticides at their LC₁₀, LC₃₀, and LC₅₀ concentrations. Results: M. brassicae was more susceptible to chlorantraniliprole (LC₅₀ = 0.35 mg/L) than indoxacarb (LC₅₀ = 1.71 mg/L). A significantly increased developmental time was observed with both insecticides at all tested concentrations but decreases in pupation rate, pupal weight, and emergence were limited to the LC₅₀ concentration. Reductions in both the total number of eggs laid per female and the egg viability were observed with both insecticides at their LC₃₀ and LC₅₀ concentrations. Both female calling activity and the sex pheromone (Z11-hexadecenyl acetate and hexadecenyl acetate) titer were significantly reduced by chlorantraniliprole in LC₅₀ concentration. Antennal responses of female antennae to benzaldehyde and 3-octanone were significantly weaker than controls after exposure to the indoxocarb LC₅₀ concentration. Significant reductions in the enzymatic activity of glutathione S-transferases, mixed-function oxidases, and carboxylesterases were observed in response to both insecticides.

The cowpea aphid (Aphis craccivora Koch) is considered a serious insect pest attacking several crops. We carried out biochemical studies to elucidate the role of the metabolising enzymes in conferring resistance to thiamethoxam, in two strains (resistant and susceptible) of the cowpea aphid. Bioassay experiments showed that the thiamethoxam selected strain developed a 48 fold resistance after consecutive selection with thiamethoxam for 12 generations. This resistant strain also exhibited cross-resistance to the tested carbamates; pirimicarb and carbosulfan, organophosphorus (malathion, fenitrothion, and chlorpyrifos-methyl), and the neonicotinoid (acetamiprid). Synergism studies have indicated that S,S,S-tributyl phosphorotrithioate (DEF), a known inhibitor for esterases, increased thiamethoxam toxicity 5.58 times in the resistant strain compared with the susceptible strain. Moreover, the biochemical determination revealed that carboxylestersae activity was 30 times greater in the resistant strain than in the susceptible strain. In addition, the enzyme activity of glutathione S-transferase (GST) and mixed function oxidases (mfo) increased only in the resistant strain 3.7 and 2.7 times, respectively, in relation to the susceptible (the control). Generally, our results suggest that the higher activity of the detoxifying enzymes, particularly carboxylesterase, in the resistant strain of the cowpea aphid, apparently have a significant role in endowing resistance to thiamethoxam, although additional mechanisms may contribute