Intraguild Predation And Combine Release Effects In The Phytoseiid Mites Amblyseius Swirskii And Neoseiulus Cucumeris

Amblyseius swirskii is an exotic phytoseiid generalist,and Neoseiulus cucumeris is a commercially widely used phytoseiid species,which was mainly used as biocontrol agents of Bemisia tabaci and the Western flower thrips Frankliniella occidentalis,respectively.In this thesis,these two species of predatory mites and their shared prey?Extraguild prey,Extra-prey?B.tabaci or F.occidentalis was used as the research system to study the Intraguild predation?IGP?by evaluating the intensity of aggression between these two phytoseiid species,the predation preference,the effects of different densities of Extra-prey on the IGP,and the effects of joint release in greenhouse.The results will provide the basis for the application of exotic A.swirskii and combine release of different phytoseiid mite species in biocontrol.The main results were as follows:?1?In the absence of Extra-prey,A.swirskii and N.cucumeris were preferentially engaged in an asymmetric IGP??² test,?²=4.631,df=1,P=0.032?,which 63.16%of A.swirskii became IG-predator whereas 36.84%of N.cucumeris became IG-predator.There were significant differences of predation on heterogeneous egg,larvae and nymphs for female adults of N.cucumeris or A.swirskii(N.cucumeris:F_2,57=59.49,P<0.001;A.swirskii:F_2,57=344.42,P<0.001).Both the two species of predatory mites were able to complete their normal growth and development,respectively?2?In the no-choice experiments of IG-predator for IG-prey and Extra-prey,there was a much significant difference in the feeding time among IG-prey and two species of prey(ANOVA:F_2,87=7.88,P=0.001).When A.swirskii was as a IG-predator,its preference for prey was in an order of eggs of B.tabaci?COX risk regression:R=18.548,P<0.001?>1^st instar nymph of B.tabaci?R=11.47,P<0.001?>2^nd instar nymph of B.tabaci?R=6.74,P=0.031?>1^st instar nymph of F.occidentalis?R=6.13,P=0.012?>3^rd instar nymph of B.tabaci?R=5.53,P=0.028?>larvae of N.cucumeris?R=0.537,P=0.387?,successively.Therefore,when Extra-prey B.tabaci(egg,1^st instar nymph,2^nd instar nymph,3^rd instar nymph)or F.occidentalis(1^st instar nymphy)was present,A.swirskii would not pose a threat to N.cucumeris.?3?In the choice experiments of IG-predator for IG-prey and Extra-prey,the IG-predator A.swirskii showed an extremely significant preference for Extra-prey of 1^stt instar of F.occidentalis over IG-prey?Breslow tests:?²=12.98,df=1,P<0.001?.Similarly,the IG-predator A.swirskii showed an extremely significant preference for Extra-prey of eggs of B.tabaci,1^st instar of B.tabaci,2^nd instar of B.tabaci over IG-prey?Breslow tests:all P's<0.01?.Therefore,when Extra-prey and IG-prey co-existed,IG-predator A.swirskii preferred Extra-prey to IG-prey.?4?The differences of predation of IG-predator A.swirskii to IG-prey and Extra-prey were compared under three different Extra-prey densities?no,insufficient,and sufficient?.With the increase of Extra-prey density,the predation of IG-predator on Extra-prey increased significantly(ANOVA,B.tabaci:F_2,57=1188.164,P<0.001;F.occidentalis:F_2,57=52.804,P<0.001).Meanwhile,the predation of IG-predator on IG-prey decreased significantly(ANOVA,B.tabaci group:F_2,57=7.363,P<0.001;F.occidentalis group:F_2,57=5.062,P=0.009).Thus,the increase of Extra-prey density reduced the IGP risk as a result of IG-predator shifting to prey on more Extra-prey.?5?In the greenhouse experiment with 4 treatments of single release of A.swirskii,single release of N.cucumeris,combined release of two kinds of predators and no release of predators,the results showed that there were significant effects of treatments on the population of both kinds of prey(GLM,B.tabaci:F_2,21=39.535,df=3,P<0.001;F.occidentalis:F_2,21=6.698,df=3,P=0.002)exhibiting that 3 treatments with predators suppressed the prey population significantly.