Intraguild Predation And Cannibalism In The Phytoseiid Mites Neoseiulus Barkeri And Neoseiulus Cucumeris

Neoseius barkeri and Neoseiulus cucumeris are generalists of phytoseiid mites which were main preying on spider mites and thrips,etc.The past studies in our lab showed that two species of phytoseiid mites N.barkeri and and N.cucumeris preferentially engaged in intraguild predation(IGP)in absence of prey,and moreover N.barkeri was most probably a potential intraguild predator(IG-predator)and whereas N.cucumeri was a potential intraguild prey(1G-prey)when intraguild predation occurred between N.barkeri and N.cucumeris.In this thesis,two different species of shared preys,Tetranychus truncatus or Framklinie occidentalis,was chosen as extraguild prey(EG-prey)to further study the intraguild predation and cannibalism between N.barkeri and N.cucumeris,respectivelly.The density dependent effects of two species of EG-prey on IGP were evaluated.Moreover,the predation preference of IG-predator between IG-prey and EG-prey were observed and the risk of IG-predator to IG-prey was assessed by Cox regression analysis model.Furthermore,the cannibalism in two species of phytoseiid mites were studied,as well.The results will provide a basis for reasonable management and combined release of two species of phytoseiid mites in biological control.The main results are as follows:1.The studies of IGP with three different density of EG-prey(no EG-prey,insuicien,EG-prey and sufficient EG-prey)showed that the density of any kind of EG-prey had significant effects on IGP.With the increase of the density of EG-prey,the frequency of IGP and cannibalism decreased whereas frequency of IG-predator preying on EG-prey increased Therefore,the increase of the density of EG-prey inhibited the IGP and the cannibalism in phytoseiid mites of N.barkeri and N.cucumeris.2.To compare the IGP of two species phytoseiid mites in the presence of EG-prey(T.truncalus or F.occidentali.s)at the same density showed that the predation rate of' N.barkeri on N.cucumeris larvae was significantly higher than that of N.cucumeris on N.barkeri larvae,which further proved that N.barkeri is the IG-predator in IGP between N barkeri and N.cucumeris.3.In no-choice test,Kaplan-Meier survival analysis indicated that the aggressiveness preference of N.barkeri for prey was in an order of the larvae of T.truncatius,the larvae of heterospecific phytoseiid mite and then the Ist larvae of F.occidentalis(Breslow tests:x2=21.98;df=2;P<0.001)whereas the aggressiveness preference of N.cucumeris for prey was in an order of the lst larvae of F.occidentalis,the larvae of T.iruncatus and then the larvae of heterospecific phytoseiid mite(Breslow tests:x2=66.40;df=2;P<0.001).4.In choice test,the results from the Cox regression model showed that when T.truncatus as EG-prey,N.barkeri had lower threat to N.cucumeris with the regression coefficient of-3.110 which indicated N.barkeri prefered T.truncatus to N.cucumeris;whereas when F.occidentalis as an EG-prey,N.barkeri had higher threat to N.cucumeris with the regression coefficient of 1.344 which indicated N.barkeri prefered N.Cucucumeris to F.occidentalis and therefore resulting IGP.Therefore,the IGP should be considered when N.barkeri and N.cucumeris were combined to release to control F,occicdentalis,5.We didn't observe the cannibalism in N.barkeri and N.cucumeris preying on conspecific adults,which indicated the cannibalism of phytoseiid mites are mainly preying on conspecific larva.