Abstract: 【Aim】To clarify the effects of methyl jasmonate (MeJA) treatments on the growth and detoxifying metabolic abilities of insects, and the effects of MeJA fumigation on the relationship between plant defense and insect detoxifying metabolism. 【Methods】 The influences of feeding MeJA and MeJA fumigation on the growth and the activities of detoxifying enzymes in the late 3rd instar larvae of H. armigera were examined, and the changes of detoxifying enzymes in H. armigera larvae, which fed the MeJA-sprayed cotton leaves after fumigation with MeJA, were also studied. 【Results】 Feeding MeJA and MeJA fumigation produced different effects on the growth and the detoxifying abilities of H. armigera larvae. Feeding the artificial diet containing 2.9 μg/g MeJA inhibited the growth of H. armigera larvae, and induced 1.92-fold increase in P450 activities. However, after fumigation with MeJA, no significant effects on the growth of H. armigera larvae were observed, while the activities of P450 and carboxylesterases (CarEs) increased to 2.94 and 1.16 times as high as the control, respectively. The P450 activities in H. armigera larvae, which experienced MeJA fumigation firstly and then fed the normal or MeJA-sprayed cotton leaves, were significantly induced, and H. armigera larvae, which fed the MeJA-sprayed cotton leaves after fumigation with MeJA, exhibited the highest P450 activity. 【Conclusion】MeJA fumigation induces the P450 related detoxifying abilities, and increases the detoxifying abilities in H. armigera against cotton defense responses induced by MeJA.

Key words: Helicoverpa armigera, cotton, plant defense, MeJA, growth, P450 enzymes, detoxifying enzyme