Study On The Sensitivity Of Two Dominant Natural Enemies To Common Insecticides In Greenhouse

The pesticides used in long term for control of pests can induce resistance in insects.The use of natural enemies can't induce resistance in pest but will control pest slower than the use of pesticides which will control the pest rapidly.The use of pesticides to control pest population will also affect the natural enemies of that pest by affecting its parasitic capability.In this paper the sensitivity of two different natural enemies Encarsia formosa and Harmonia axyridis were discussed against eight kinds of spraying pesticides(avermectin,nitenpyram,imidacloprid,thiamethoxam,cyantraniliprole,sulfoxaflor,pyriproxyfen,acetamiprid)and three kinds of fumicants(chlorothalonil,moroxydine,isoprocarb-pyridaben).The results are as follows:1.The sensitivity of Adults of E.formosa against eight insecticides was significantly different,screened out five moderate toxicity and three safe insecticides for E.formosa.The results showed that for E.formosa the mortality rate was the lowest i.e.42% by pyriproxyfen.The larvae stage of E.formosa was more sensitive than that of pupa.The longer pesticides residue remains,the parasitic ability of E.formosa and lethal effect was lower.But significantly difference was noticed between the residual periods of each agents,when the residue was seventh day,the agent showed hormesis on the parasitic ability of E.formosa,and the parasitic ability of E.formosa was 7.07,7.13,7.13 and 6.8 when the pesticides imidacloprid,thiamethoxam,cyantraniliprole and acetamiprid were used respectively which was significantly higher than 5.47 of the control group.2.Adults of H.axyridis against eight insecticides showed fewer death rates which were less than 50% which was the sensitivity rate.The sensitivity of H.axyridis to insecticides at different developmental stages was different i.e.egg and larvae stages were more sensitive as compared to pupae and adult stages.Pyriproxyfen and avermectin on H.axyridis eggs showed the highest death rate i.e.89% and 92% respectively.There was a positive correlation between the residual period of eight agents and the feeding behavior of H.axyridis i.e.longer the residual period,the H.axyridis feed on more aphids,but the feeding ability at seventh days was still significantly lower than the control.3.E.formosa was tested with three kinds of fumigants at different times(4 h,8 h,12 h and 24 h)and was tested for feeding ability on nymph as compared to control treatment which showed a significant inhibitory effect.Significant difference was noticed between the three kinds of agents.The results indicated that due to the use of fumigants,feeding ability of E.formosa was significantly inhibited as compared to the use of spraying insecticides i.e.feeding ability was affected more by the use of fumigant pesticides.After 24 hours of treatment of three kinds of fumigants,the number of parasitized whiteflies was significantly lower than the control group,the isoprocarb-pyridaben and chlorothalonil had no significant difference on the number of parasitoid E.formosa treatment at different time,and the virus spirit after treatment the number of parasitoid E.formosa along with the increase of processing time significantly increased.Three kinds of fumigants can produce lethal effects on E.formosa were in the range of 4 ~ 24 h,the death rate of isoprocarb-pyridaben was significantly higher than that of chlorothalonil and virus spirit.4.The death rate of H.axyridis by isoprocarb – pyridaben was significantly higher than that of chlorothalonil and virus spirit.The feeding number of H.axyridis were significantly inhibited at different times when three different kinds of fumigant pesticides were used.There was no significant difference between the treatment,but the feeding amount within 24 h were significantly lower than that of control group which showed the same trend with the role of E.formosa.All the above results showed that the sensitivity of E.formosa to acetamiprid,cyantraniliprole and pyriproxyfen was low i.e.showed high safety index.Eight kinds of spraying insecticides were moderately toxic to H.axyridis i.e.showed moderate mortality rate in the field for which the recommended concentration will be below 50%.Certain degree of toxicity was showed by isoprocarb-pyridaben fumicants when were used against E.formosa and H.axyridis.Three kinds of fumigant pesticides showed some inhibitory effects on two kinds of natural enemies feeding and parasitism.