| Larch is the main tree species in Northeast China, which often suffered serious harm by pests. In this paper, Larix gmelinii and Lymantria dispar, one of the main pests were chose as target to study the impact of induced resistance of larch on growth, digestive enzyme and detoxification enzyme of Lymantria dispar by means using methyl jasmonate (MeJA), jasmine ketone, Lymantria dispar larva feeding, Dendrolimus superans larva feeding to deal with 3 year old larch seedlings. We discussed the impact mechanism of exogenous factors on induced resistance in larch, and Lymantria dispar's physiology response mechanism on the plant defense material. It provides a basis theoretical to improve forest health and effective control of Lymantria dispar population density. The conclusion as follows:1. The Larch induced resistance by different factors affects the growth of Lymantria disparLarch induced resistance by exogenous factors can inhibit the growth of Lymantria dispar which reflected in weight loss of different ages of larvae, larval survival reduced, pupal weight decreased, fecundity of adults reduced, and the population numbers of Lymantria dispar reduced. Insect resistance of Larch induced by different factors are different, of which the growth index of Lymantria dispar eating larch induced by Lymantria dispar feeding, lower than the ones induced by Dendrolimus superans feeding. Larch spraying MeJA had the greatest impact on Lymantria dispar larvae, weight, pupal weight and fecundity of adults in 4 ages significantly lower than other treatments of larvae. It showed that exogenous compounds and insect feeding can both induce a defense response of larch, and methyl jasmonate had the best effect.2. Larch induced resistance by different factors had interference on the digestive enzymes activities of Lymantria disparAfter Lymantria dispar larvae feeding larch induced by different factors, total protease, alkaline trypsin and chymotrypsin inhibitory activity decreased significantly(P<0.01), while alkaline trypsin activity was significantly increased (P<0.01) compared with the control. That indicated the larch induced resistance had strong interference on the digestive enzymes activities of Lymantria dispar. The induction of Larch induced Jasmonates on total protease, alkaline protease, chymotrypsin activity was stronger than insect feeding induced, larvae enzyme activity significantly less than insect induced(P<0.05), showed that exogenous compounds induce larch protease inhibitors had stronger interference; and insect feeding induced alkaline protease activity was significantly increased, probably because of effective blocked the expression of some defense gene of larch, reducing the synthesis of the enzyme inhibitor.3. Larch induced resistance by different factors had interference on the detoxification enzymes activities of Lymantria disparThe larch induced resistance by different factors disturbs the detoxification enzymes activities of Lymantria dispar larvae, including acid phosphatase (ACP), alkaline phosphatase (AKP), carboxylesterase (CarE), and glutathione S-transferase (GSTs). After feeding larches dealt with different factors, the ACP activity of larvae was significantly lower than control (P<0.01). In addition, the AKP activity increased first and then decreased after feeding the larches induced by Lymantria dispar, however, the activities of AKP were all inhibited lower than control (P<0.05 or P<0.01) induced by three other methods. Compared with the control, CarE activities were inhibited in varying degrees and showed significant differences. GSTs activity changes are different, of which enzyme activity of larvae was significantly lower than the control after feeding larches dealt with MeJA and Lymantria dispar feeding (P<0.01), while activity was significantly higher than the control after feeding the larches dealt with the other two methods (P<0.05或P<0.01). It explained that larch resistance induced by Lymantria dispar feeding can affect the detoxification mechanism of follow-up feeding in those same stocks. That is the integrated performance between induced resistance of larch and intraspecific competition of insects. MeJA, as an exogenous plant hormones, can induce larch resistance and effectively inhibit the detoxification of those follow-up feeding those were very similar to the Lymantria dispar larvae feeding in impression of action.Larch can rapidly induced production of defense material after stress by external factors, which has a negative impact on growth and development of Lymantria dispar. Larch induced by Insect feeding and jasmonic acid derivatives can significantly affect the digestive enzymes and detoxification enzyme activity of Lymantria dispar larvae, disturb normal metabolism of insects, and thus achieve the purpose of insect resistance. Methyl jasmonate as an inducer of plant insect-resistant, has better effect than the ones induced by insect feeding, that has a wide range of applications in ecological control of the Lymantria dispar, reduce environmental pollution and maintaining ecological balance etc.
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