Effects Of Three Insect Growth Regulators On Bemisia Tabaci (hemiptera: Aleyrodidae) And Its Parasitoid Encarsia Formosa (hymenoptera: Aphelinidae)

Bemisia tabaci (Gennadius)(Hemiptera: Aleyrodidae) is one of the most serious pests inmore than90countries and districts in tropical, subtropical regions and adjacent temperatezones. Whitefly outbreaks in the world causing serious economic losses. Because ofwidespread use of chemical pesticides, pests resistance increased significantly. Encarsiaformosa Gahan is an important parasitoid of whiteflies and is widely used on greenhousecrops as an important whitefly biological control agent. Generally, it is difficult to achieveideal control effects by using natural enemies alone. The combination of biological controland chemical control has broad application prospects.In this thesis, I reported the results of four experiments:(1) deteremined the toxicities ofthree insect growth regulators (IGRs), pyriproxyfen, fenoxycarb and buprofezin to nymphalstages of B. tabaci in the laboratory;(2) determined the effects of the IGRs on E. formosalarvae, pupae and adults in the laboratory;(3) evaluated the effects of the IGRs on E. formosaadults foraging, and (4) evelaued the effects of both IGRs and E. formosa to control B. tabaciin the greenhouse.The results of the experiments were summarized as follows:(1) Pyriproxyfen had the strongest ovicidal effect on the whitefly, with the LC50of1.084mg/kg, and had a high activity against young nymphs, with the LC50of41.491mg/kg.However, its toxicity against elderly nymphs was low. Fenoxycarb had a strong ovicidal effect,with the LC50of2.965mg/kg, and had a certain activity against young nymphs. But, it had noeffect on elderly nymphs. Buprofezin had a high activity against young nymphs, with theLC50of118.940mg/kg. However, its ovicidal effect was low, with the LC50of1614.290mg/kg. (2) All three IGRs had toxic effects on E. formosa larvae. The emergence rate of E.formosa was0if pyriproxyfen was used on the recommended field rate; Fenoxycarb was36.4%and Buprofezin was19.6%. Pyriproxyfen was seriously harmful to E. formosa larvae;Fenoxycarb was slightly harmful and buprofezin was moderately harmful. The effect of IGRson E. formosa pupae was apparently smaller than larvae. The emergence rate of E. formosawas just7.7%if pyriproxyfen was used on the recommended field rate; while those offenoxycarb and buprofezin were86.2%and83%respectively. Pyriproxyfen was moderatelyharmful to E. formosa pupae. However, both fenoxycarb and buprofezin belonged to safeinsecticides.(3) Using leaf dipping method to test the effect of the three IGRs on E. formosa adults, themortality of E. formosa adults was lower than30%. According to the standards of IOBC, theyare safe insecticides. However, pyriproxyfen and fenoxycarb are slightly harmful to adult E.formosa if using glass-vial bioassay method.(4) Spraying IGRs on tomato leaves without B. tabaci nymphs, the toxicity of fenoxycarbto E. formosa had significantly increased after24h. After aging for72h and168h in agreenhouse, IGR residues did not adversely affect parasitoid survivorship in comparison towater controls. Spraying IGRs on tomato leaves that had B. tabaci nymphs, the toxicity ofpyriproxyfen and fenoxycarb significantly increased after24h posttreatment, Highest levelsof parasitoid mortality was still on pyriproxyfen and fenoxycarb-treated leaves after72h.After aging for168h, IGR residues had similar parasitoid survivorship rates and had nodifference with water controls.(5) The results of simulating field trials demonstrated that pyriproxyfen had the strongesttoxic effects on B. tabaci, but it caused the lowest emergence rate of E. formosa, and was themost unsafe insecticide among the three IGRs. Buprofezin had a high activity against B.tabaci. It had the lowest effect among the three IGRs on E. formosa parasitism and emergencerate. So it was the most safety insecticide. Fenoxycarb had some toxic effects on B. tabaci andwas slightly harmful to E. formasa.