Oviposition Strategy Of Chouioia Cunea Yang(Hymenoptera:Eulophidae)

The fall armyworm Hyphantria cunea is an invasive insect pest,serverly damaging trees in northern China.Biological control of the fall armyworm using the parasitoid Chouioia cunea Yang has offered a considerable potential.As of this time many studies have been done on the its application to biological control.However,less focus has been given on the behavioral ecology of the gregarious parasitoid.This thesis study was designed to identify factors that can affect C.cunea in making decisions on clutch size and sex ratio.The main results and conclusions obtained from this study are summarized as follow.1.Clutch size and sex ratio in response to host body size and foundress numbersTo investigate ovipsotion tactics of C.cunea in response to mother wasp density and A.pernyi pupa body size,seven categories of mother wasp density,30,50,70,100,130,150 and 180,were manipulated,which were provided with a host varied cross a broad range in body weight.The study showed that the proportion of male offspring wasps increased with increasing clutch size.The body size of offspring parasitoids decreased with increasing mother wasp density.Under the same mother wasp density,clutch size and offspring body size increased with host body weight at parasitism.The results of this study suggest that C.cunea can adjust oviposition strategy according to host size and mother wasp density.2.Effects of foundress competition experience and host body size on oviposition tacticsTo understand how intraspecific competition affects females in making their decisions on oviposition,individually exposed weighted H.cunea pupae were exposed to female wasps with or without the experience of grouping with conspecific wasps,and sex ratio,clutch size and longevity of offspring parasitoids were examined.The results showed that when mother wasps had the experience of competition,male proportion in offspring parasitoids increased.But the competition treatment had no significant effect on clutch size and adult longevity.When mother wasp density was constant,host body weight had a significantly positive effect on the longevity and clutch size.The results of this study suggest that competition experience had an effect on oviposition strategy of C.cunea.3.Oviposition strategy in response to temperature and host body sizeTo examine the influence of temperature on sex ratio,development duration,clutch size and adult longevity,three temperature treatments,20?,25? and 30?,were tested,using A.pernyi pupae as hosts.The results showed that 20? was best for female proportion in offspring production,followed by 25?,and then by 30?.Furthermore,adult longevity and developmental duration of offspring parasitoids decreased with increasing temperature.Clutch size was largest at 25?,followed by that at 30?,and then by that at 20?.At the same temperature,adult longevity of offspring decreased,while male proportion and clutch size increased,with increasing host body weight.Host body weight did not affect developmental duration of offspring parasitoids.These results suggest that 25 ? was optimal for C.cunea,as manifested by adult longevity,clutch size and developmental duration.4.Effects of supplementary food,temperature and mother wasp body size on offspring longevityTo provide data for effective mass-production of the parasitoid C.cunea,a factorial combination of wasp body size(2 levels),supplementary food(2 levels)and temperature(3 levels)treatments was manipulated using Antherea pernyi pupa as the host in laboratory trials to examine the survival to adult.The survival analysis found a significant three-way interaction effect among the three factors on survivorship to adult.The adult survival probability varied between temperature treatments under different treatment combinations of body size with food,decreasing with increasing temperature.Adult longevity significantly differed between temperatures under combination treatments between food with body size,being greater at 20 ? than at 25 ?,and in temperatures of 25 ? than of 30?.The results of this study suggest that temperature,supplementary food and female body size can be in interaction in affecting C.cunea longevity.