Depressed performance and detoxification enzyme activities of Helicoverpa armigera fed with conventional cotton foliage subjected to methyl jasmonate exposure

Methyl jasmonate (MeJA)-mediated defense in conventional cotton, Gossypium hirsutum L. (Malvaceae), against cotton bollworm, Helicoverpa armigera (H€ ubner) (Lepidoptera: Noctuidae), was investigated with respect to the activities of the detoxification enzymes acetylcholinesterase (AChE), carboxylesterase (CarE), and glutathione S-transferases (GST) in pupae as well as the performance of larvae. The results suggested that exogenous application of MeJA to cotton leaves depressed the activities of AChE, CarE, and GST of cotton bollworm pupae. Both the absolute and protein-specific AChE activities of pupae were depressed at all three MeJA concentrations applied as compared with a control, and the effects of 0.4 mMMeJA were significantly higher than those of 0.1 and 0.2 mM. A marked reduction in absolute CarE activity was observed at the 0.4 mM MeJA treatment, whereas the protein-specific activity was increased by 0.2 and 0.4 mM. Absolute GST activity was significantly depressed only by the 0.4 mM MeJA treatment, whereas protein-specific GST activity was not markedly affected by MeJA. Protein content of pupae was reduced by 0.4 mM MeJA-induced defense in cotton leaves. The development time of larvae was protracted and pupal weight was reduced by 0.1 and 0.4 mM MeJA-treated cotton leaves. Larval weight gain was inhibited significantly on 0.2 and 0.4 mM MeJA-treated cotton leaves. The results suggested that MeJAinduced plant defense may have adverse effects on H. armigera. In addition to the inhibition of growth and development, induced defense may also impair the insect’s ability to detoxify toxic plant secondary metabolites.