Effects of partially spraying Larix olgensis seedlings with exogenous methyl jasmonate on the defensive enzyme activities of Dendrolimus superans larvae

In order to investigate the effects of exogenous methyl jasmonate on the detoxification metabolism of Dendrolimus superans larvae, three concentrations of methyl jasmonate (MeJA, 0.01, 0.10 and 1.00 mmol/L) were sprayed partially onto lateral branch of Larix olgensis seedlings; and the protective and detoxification enzyme activities of the 3rd-5th instars of Dendrolimus superans larvae that fed on these seedlings were analyzed. Our results showed that exogenous applications (partial sprays) of methyl jasmonate at three different concentrations on larch seedlings had significant effects on both the protective and detoxification enzyme activities of Dendrolimus superans larvae (P < 0.05) with similar trends, but were concentration-independent. The SOD and POD activities of the 4th instar larvae in each treatment group were significantly higher than those in CK (P < 0.05), but the differences were not significant for the 3rd and 5th instars (P>0.05). The ACP, AKP and GST activities of D. superans larvae in the MeJA treated groups were slightly lower than those in CK at the 3rd instar, and were significantly lower than those in CK at the 4th instar (P < 0.05), but were to some extent higher than those in CK at the 5th instar. The above results indicate that partially spraying exogenous methyl jasmonate can increase the induced systemic resistance of Larix olgensis against various defoliators, such as D. superans by disturbing its detoxification and metabolism mechanisms. However, D. superans larvae, in turn, might respond and even adapt to the induced systemic resistance of larch trees by quickly increasing the bio-activities of their protective and detoxification enzymes.