Foraging Decisions On The Cotton Mealybug Patch In Resposnse To Survival Risks In Aenasius Arizonensis(Hymenoptera:Encyrtidae)

Herbivorous insects are usually distributed in discrete patches in the environment.According to optimal foraging theory,parasitoids make optimal decisions to make efficient use of time on a host patch by assimilating the information about ever changing environmental variables and their own physiological states.In many studies of patch foraging behaviors in parasitoids,more attention has been given to the characteristics of hosts and foraging parasitoids than to those of external factors such as survival risks posed by natural enemies of the parasitoids,especially by their own parasitoids or hyperparasitoids of their hosts.My thesis research was focused on gregarious Aenasius arizonensis Girault attacking alien cotton mealybug Phenacoccus solenopsis Tinsley,to examine its patch-leaving decisions and foraging behaviors at the risk of being attacked by either predaceous ladybird beetle Harmonia axyridis Pallas or the hyperparasitoid Cheiloneurus nankingensis Li et Xu,which is a new species found in my study attacking the mealybug that has been parasitized by A.arisonenesis.My study indicates that the presence of H.axyridis on the patch increases the patch-leaving tendency of A.arisonenesis but the existence of the hyperparasitoid is not influential on the patch-leaving tendency.These findings provide novel empirical evidence for understanding foraging behavior ecology of parasitoids.What follows is a summary of main results and conclusions obtained from my study.1.Patch foraging behavior of A.arizonensis at risk from predationHost patches of P.solenopsis were established on broad bean seedlings at the density ranging from 10 to 28 per plant and one 2^nd instar larva of H.axyridis was then moved onto the leaf with mealybugs（a patch）.A female A.arizonensis wasp was released on the patch and continuously observed for its foraging behaviors until leaving from the patch.The Cox proportional hazard model was run to fit the parasitoid’s patch residence time as a function of covariates to estimate patch-leaving tendency of the parasitoid.The results showed that in the presence of H.axyridis,A.arizonensis females increased their patch-leaving tendency by 4.35 times higer than that in the control,and this tendency did not change with host density.They decrease the patch leaving tendency with an increase in the frequency of ovipositor’s sting or the giving-up time（the interval between the last stinging and leaving the patch）.Generalized linear models were run to analyze foraging behaviors on host patches.The results showed that the presence of H.axyridis reduced the frequency of stinging,and did not influence the frequency of antenna tapping.The frequencies of stinging and of tapping increased with host density.The results from the current study suggest that A.arizonensis increases its patch leaving tendency at the risk of predation.2.Description of a new hyperparasitoid species from attacking P.solenopsisA hyperparasitoid of the cotton mealybug was found in eastern China attacking the cotton mealybug that had been parasitized by A.arizonensis.It was identified as a new species of Cheiloneurus（Hymenoptera:Encyrtidae）and named as C.nankingensis sp.nov.after the name of the city where it was firstly found.It is similar to C.arabiacus Hayat,but distinct from it（in brackets）in following morphological characters.Without an infuscate area below proximal half of parastigma;scape cylindrical;pedicel as long as F1（longer than F1–F2 combined）;F3 quadrate or slightly broader than long（F3 longer than broad）;F4–F6 broader than long（F4,F5 quadrate）;clava shorter than F4–F6 combined（longer than F4–F6 combined）;head in frontal view higher than broad（broader than high）;mandible with three acute teeth（with two acute and one round teeth）.The new hyperparasitoid is an obligate parasitoid of A.arizonensis.3.Patch foraging behavior of A.arizonensis at risk from hyperparasitismMealybug patches were set up on broad bean seedlings at continuously variable host densites from 13 to 28 per plant,and then one female adult of C.nankingensis was introduced onto the host patch as a risk factor.One female A.arizonensis wasp was released and followed to record its foraging behaviors.The Cox proportional hazard model was run to fit the patch residence time of the parasitoid as a function of the treatment factors and relevant covariated behaviors performed on the patch.The modelling results showed that the presence of a hyperparasitoid did not influence the patch leaving tendency of A.arizonensis.The analyses of foraging behaviors demonstrated that both the frequency of ovipositor stinging and that of antenna tapping were not affected by the presence of the hyperparasitoid.Increasing host density shortened the patch residence time and increased the frequency of stinging,but did not influence the frequency of antenna tapping.The results from the current study suggest that the presence of the hyperparasitoid is not influential on patch-leaving decision and oviposition behavior of A.arizonensis.