| 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. Spinosad is a class of macrolide compounds which has been tested extensively on a global basis since 1990. It demonstrates rapid contact and ingestion activity in insects, which is unusual for a biological product. The mode of action of spinosad is characterized by excitation of the insect nervous system, leading to involuntary muscle contractions, prostration with tremors, and paralysis. These effects are consistent with the activation of nicotinic acetylcholine receptors by a mechanism that is clearly novel and unique among known insect control products. Meanwhile, Spinosad has relatively low toxicity to mammals and birds and is only slightly-to-moderately toxic to aquatic organisms. In addition, chronic toxicology tests in mammals have shown that spinosad is not carcinogenic, teratogenic, mutagenic or neurotoxic. In order to study the biological activity and mechanism of spinosad, its bioactivity against the different instar larvae of L. dispar and its effect on the development, the activities of detoxifying enzymes and protective enzymes were assayed by leaf membrane method, which provided theoretical basises for the applications of spinosad and other non-steroidal ecdysone analogs in forestry and new insecticides research; Furthermore, the ulstructure of antennal sensilla were observed for the first time, which provided theoretical basises for exploring chemical communications between plants and insects, and developing environmental safe control in field.The toxic effect on the different instar larvae of Lymantria dispar were assayed by leaf membrane. The results showed spinosad on the moth, showing high activity, especially on the 3rd instar larvae.With the growth of larval age, increasing the required dose, but with the treatment time, LC50 dose decreased. LC50 of spinosad against 3rd and 5th instar larvae are 0.024 and 0.226mg·L-1, respectively. The development duration of the larva treated by LC10 and LC50 of spinosad was not significant difference with control, but larval survival rate and pupation rate were significantly lower than control (P<0.05)In order to study the insecticidal activity and mechanism of spinosad, its effect on the activities of detoxifying enzymes and protective enzymes against the 3rd and 5th instar larvals of L. dispar were assayed. The results showed the larvae of detoxification enzyme and protective enzymes activity could be interfered after treatment of spinoad. On one hand, the activities of enzymes showed different varieties after LC50 treatment of spinosad. Which carboxylesterase (CarE), glutathione-S-transferase (GST), multi-function oxidase (MFO) and alkaline phosphatase (ALP) are significantly increased firstly and decreased then(P<0.05); But for acid phosphatase (ACP), the trend of activity are decreased-increased-decreased, the difference was significant (P<0.01). On the other hand, activities of catalase (CAT) showed no significantly variaties after treatment, but phenoloxidase (PO) in the treated larvae were first activated, and then inhibited by using spinosad treatment. The activities of superoxide dismutase(SOD) and Peroxidase (POD) showed different varieties in the 3rd and 5th instar larvals of L. dispar after treatment of spinosad. Which the activities of SOD and POD in the 3rd instar larvals were first activated, and then inhibited too. The most the activities of the two enzymes were arose in the 3h to 6h(P<0.01). Whereas the POD and SOD activities in the 5th instar larvae were activated obviously, that is 1.543 and 1.716 times of CK which is in the same time, the difference was significant (P<0.01). The activities of chitinase activities showed different varieties after treatment of spinosad, which the chitinase activities in the 3rd instar larvaes were remarkable activated while that in the 5th instar larvae were inhibited obviously. And there is time effect on these activities.Antennae and their sensilla of L. Dispar were observed using scanning electron microscopy. The antennae of male moth were plumose, and those of female were pectinate. There are six different types of sensilla on the male of L. dispar: Sensilla trichoid, s. chaetica, s. coeloconic, s. basiconic, s. styloconic, and s. auricillica are present, besides the above types, there is additional type on famale antannae:s. squamiform. The antennae of male moth were plumose, and those of female were pectinate. Moreover, there were obviously sex dimorphisms, including different antenna sizes, different sensilla shapes, sizes, numbers and distributions. Using transmission electron microscopy (TEM) to illustrate the ultrastructures and possible functions of antennal sensilla of L dispar. S. trichoid and s. coeloconic were found to be olfactory receptor and chemical receptor separately.In a word, spinosad had a higher biological activity against the L. dispar, and its major detoxifying enzymes and protective enzymes in the body were significantly interfered, it had high toxic effect against the larvae, which providing a new thought to pest control, is an effective pesticide for L.Dispar; otherwise, studies on antennal sensilla would also establish a theoretical foundation on further research of insect-plant communication.
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