Sublethal Effects Of Several Insecticides Commonly Used In Rice Fields On Pirata Subpiraticus

The spider, whuch is the key group of predatory natural enemies in the rice system, play an important role in the natural control of rice pests, particularly,of rice planthoppers. In this stage, for the management of rice planthoppers, application of insecticides still occupy a dominant position. As a typical pesticide-induced resurgence pests, for brown rice planthopper Nilaparvata lugens (Stal), the destruction of natural control of the pest after insecticide spraying is one of the important mechanisms of the resurgence. Therefore, it is an important to scientificly evaluate the negative effects of insecticide on the spider groupas. be reasonablly used for selection of insecticides, and enhance natural control in paddy fields. In this study, we focused on a wolf spider Pirata subpiraticus, selected several insecticides, imidacloprid, triazophos, pymetrozine and chlorantraniliprole,which are commonly used against rice pest insects in China, studied the sublethal effects of tested insecticides on predation function, reproduction, detoxification enzymes and the immune system. The results are as follows:1.The sublethal effects of several insecticides commonly used in paddy field on predation and digestive enzymes of P. subpiraticus.The results showed that, the predation of had been negatively affected when treated with the insectcides at recommoned rates at the condition of fixed prey density, while triazophos impacted the most. Functional responses of P. subpiraticus treated with sublethal doses of insecticides were still in line with Holling â…¡ model, but model parameters had not been significantly effected. Effects of tested insecticides at sublethal doses on digestive enzymes varied with insecticide varieties, the time after treatment. The experiment indicated that treatement with triazophos significantly inhibit protease activity of the wolf spider. For the effects of imidacloprid at two sublethal doses (recommoned rate for application and LC20), the insecticide stimulated protease activity short after the treatment, but subsequent the promoting disappeared, and even showed inhibition, while pymetrozine showed similar inhibitory role in the first stimulation. The effect of chlorantraniliprole treatment was not significant on protease activity. Treatment with field recommended doses of pymetrozine and imidacloprid inhibited of lipase activity at certain degree,while the treatment of50mg/L triazophos inhibited lipase of the wolf spider significantly. 2.The sublethal effects of several insecticides commonly used in paddy field on the propagation of P. subpiraticus and its ovarian cells.Experiment indicated that the egg number produced by P. subpiraticus significantly decreased when treated the spider without egg sac with the tested insecticides at sublthal doses. while there were no effects when treated the spider with egg sac. From TEM picture of the ovarian cells, dense yolk granules in the ovarian cells of the control group was shown. which arranged in compact yolk granules. In the ovarian cells treated with pymetrozine, yolk granules occurred mainly in small and arranged in loose:in triazophos treatment, the yolk particles arranged in loose, medium-sized yolk granules, scattered small yolk granules, while in the treatments of imidacloprid and chlorantraniliprole,there were no significant effect. In triazophos treatment, the number of longitudinal ridge in the mitochondria reduced in mitochondria and endoplasmic reticulum. Significantly reduced in the number of its nucleus surrounded by mitochondria and endoplasmic reticulum. in the pymetrozine treatment, while mitochondrial structure is not clear:Chlorantraniliprole and imidacloprid treatment had no significant effect on internal endoplasmic reticulum and mitochondria.3.The sublethal effects of several insecticides commonly used in paddy field on two detoxification enzymes and the immune parameters of P. subpiraticus.The results showed that:among the several insecticide treatments, triazophos stimulated glutathione S-transferase of P. subpiraticus most and at5bioassay from4h to48h after treatment, the activity increased107.7%,26.7%,22.7%,73.3%and15.7%respectively. Imidacloprid also has a certain stimulating effect on GSTs. while formamide and pymetrozine had no significant effects. For esterase of the wolf spider, significant inhibition was found with triazophos treatment, and there were no significant effect of the three other treatmentsagents on the enzyme.Total haemocytes counts (THC), plasma cell and granulocyte cell of P. subpiraticus were significantly increased at4h,8h and12h after treatment when treated with sublethal doses of the tested insecticides, especially in the treatment of imidacloprid. At48h after treatment, inhibition were found on cell count, especially in the teatment with triazophos. Similar to the effect on blood cells, first stimulation and then inhibition effect were indicated in the effects of sublethal doses on immunization-related phenol oxidase activity.