| Gypsy moth, Lymantria dispar L. is one of the most important Lepidopteran defoliator pests all over the world. It has many characteristics, such as wide distribution, mixed food and having caused very economic loss in agriculture and forestry production, therefore, it is important to look for effective prevention and treatment. Methoxyfenozide, is also known as RH-2485, which can simulate the function of ecdysone of Lepidoptera larvae, and act on ecdysone receptor leading to the lethality during insect molting. As a non-steroidal ecdysone agonist, it had high toxic effect against the pharmaceutical Lepidoptera pests on crops and high security against the environment and non-target organisms, so it is an important tool for integrated pest management. To better study the biological activity and mechanism of methoxyfenozide, its bioactivity against the different instar larvae of L. dispar and its effect on the development, the activities of protective enzymes and detoxifying enzymes were assayed by leaf membrane method, and the expression of proteins in different tissues of L. dispar were detected, which provided theoretical basises for the applications of methoxyfenozide and other non-steroidal ecdysone analogs in forestry and new insecticides research.The toxic effect on the different instar larvae of Lymantria dispar were assayed by leaf membrane. The results showed methoxyfenozide on the moth, LC50 of methoxyfenozide against 2-6 instar larvae are 2.395,4.38911.677,16.612 and 20.984 mg/L (48 h), respectively, showing high activity, especially on the 2nd instar and 3rd instar larvae. With the growth of larval age, increasing the required dose, but with the treatment time, LC50 dose decreased. Effect of LC10 (0.274 mg/L) and LC30 (2.508 mg/L) of methoxyfenozide on the development of L. dispar found that it had some impact on morphology of L. dispar larvae indicating different abnormality. The relative consumption rate (RCR) of 4th instar larvae was significantly inhibited by treatment with LC10 dose. The LC30 dose could significantly inhibited efficiency of conversion of ingested food (ECI). The larval survival rate, the 6th instar larval weight, pupation rate and the weight of female pupae were significantly lower by treatment with LC10 and LC30 of methoxyfenozide. Besides, the lethality of LC30 concentration to the larvae and the pupae was superior to LC10 and the effect of continuously treating 4th instar larvae was superior to treating within 24 hours (P<0.05).In order to study the insecticidal activity and mechanism of methoxyfenozide (RH-2485), its effect on the activities of protective enzymes and detoxifying enzymes against the 2nd,4th and 6th instar larvals of L. dispar were assayed. The results showed the larvae of protective enzymes and detoxification enzyme activity could be interfered after treatment of methoxyfenozide. The activities of phenoloxidase, superoxide dismutase, chitinase and glutathione-S-transfer in the treated 2nd larvae were first activated, and then inhibited by using methoxyfenozide treatment. Of carboxylesterase were first activated, then inhibited and further inhibition, and the MFO-O-demethylase at first inhibited, then activated. The activities of peroxidase significantly inhibited,24 h treatment, the strongest inhibition of the enzyme for the same period in the control of 0.541 times the difference was significant (P<0.01). The activities of phenoloxidase, superoxide dismutase, peroxidase, MFO-O-demethylation and glutathione S-transfer were first activated, and then inhibited. In addition, the activities of chitinase and carboxylesterase were inhibited in the treated 4th larvae by using methoxyfenozide treatment. The activities of phenoloxidase, superoxide dismutase, peroxidase, carboxylesterase, MFO-O-demeth-ylation and glutathione S-transfer were first activated, and then inhibited. Furthermore, the activities of chitinase were inhibited (P<0.05). And there is time effect on these activities.The expression of proteins in different tissues of the 4th instar larvaes L. dispar were detected by SDS-PAGE. The results showed the protein expression of the 4th instar larvae were interfered after treatment of methoxyfenozide and the specific proteins were produced in the hemolymph tissue and epidermal tissue. After 12 h or 24 h, the protein expression of the haemolymph and midgut were increased or decreased and we found two new protein bands in hemolymph tissue after treatment of methoxyfenozide.48h later, the protein expression on the epidermal tissue is extremely obvious, a molecular weight of 17-25 kDa,30 kDa,30-46 kDa protein expression were lower than the Department's control group, but in 25-30 kDa, 46-58 kDa Department protein expression was significantly increased and a specific proteins were produced in nearly 80 kDa.These results indicated that methoxyfenozide as a non-steroidal ecdysone agonist had a higher biological activity against the L. dispar, and its major protective enzymes and detoxifying enzymes in the body were significantly interfered and the specific protein were produced in the hemolymph, midgut and epidermal tissue, showing methoxyfenozide had high toxic effect against the L. dispar, which providing a new thought to pest control, otherwise, studies on the expression of proteins in different tissues wohld also establish a theoretical foundation on demonstrating the mechanisms of insect molting and the new pesticide research.
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