Behavior Ecology Studies Of Host Foraging Of Meteorus Pulchricornis (Hymenoptera: Braconidae)

Meteorus pulchricornis, a widely distributed parasitoid in Palaearctic region. is a solitary endoparasitoid of numerous insect pests in agricultural crops and forest trees, including gypsy moth, Lymanstria dispar (L.), beet army worm, Spodoptera exigua Hubner, and cotton bollworm, Helicoverpa armigera (Hubner). Even though bionomics of this parasitoid has been reported, foraging behavior is little known. This thesis study was designed from both indoor and outdoor experiments, to address how host-foraging behaviors of uniparental strain of M. pulchricornis were influenced by a range of factors, including physiological state, experiences obtained from emergence site and foraging, food plants for host larvae, and spatial constraints. The studies should contribute to understanding underlying ecological mechanisms of foraging behaviors in parasitoids. The main results and conclusions obtained from these studies are summarized as follows.1. Flight ability of M. pulchricornis adult at the age of 1-day,5-day,10-day,20-day, and 30-day old was measured by a flight-mill system with 32 channels. The result showed that flight performances of 5-day old wasp, in take-off time, total flight time, average velocity, and the longest single flight duration, were significant better than those of other aged wasps. The middle-aged wasp (10-day old), though having a higher egg-load than the younger and older wasps, is was weaker in flight ability, which suggested that egg-load might influence flight ability of parasitoids.2. Host-foraging behavior of M. pulchricornis was studied as affected by food plants with host larvae in the wind tunnel, the large cage and the walk-in field cage.. The parasitoid obviously preferred host larvae together with plants to either host larvae or plants. The wasp favored host larvae on soybean plant than on the other plants, as indicated by number of visits, ovipositor drillings, and parasitism rate.3. Learning while foraging was studied in the wind tunnel, as affected by different host species associated with soybean plant. The parasitoid showed more behavioral responses to H. armigera and S. exigua host larvae that were together with soybean plant (host-plant complex) than to either host larvae or soybean plant. The experience of successful foraging and oviposition for a naive wasp did not affect follow-up behavioral responses to plant-host larvae complexes. However, a successive experience of foraging and oviposition on different plant-host larvae complexes led the wasp to prefer the complex that was recently experienced. The results suggested that learning while foraging plays an important role in M. pulchricornis, and that effects of such leaning depend on the plant identity with which host larvae were feeding. M. pulchricornis did not show significant preferences for either H. armigera-or S. exigua-soybean plant complexe.4. Host-patch foraging behaviors were observed in a large transparent cage, and the time spent on host-patches was fitted by the Cox proportional hazard model to gain insight into mechanisms for patch-leaving behaviors. The parasitoid paid more initial visits to, stayed longer on, launched more attacks on, and made more re-visits to host patches with higher host densities. The residence time on patch increased with increase of host density if oviposition was accomplished on the patch,but decreased with increase of host density if without. Thses performances were in accordance with the projection of the Marginal Value Theorum. The Cox modeling results indicated that (ⅰ) host density, number of visits, and parasitism rate contributed to longer residence on host-patches, which lend support to the'incremental mechanism'; (ⅱ) but the interactions of these variables accelarated patch-leaving, which lend support to the'decremental mechanism'.5. Host-instar selection behaviors of M. pulchricornis in the small and large arenas under lab conditions were observed using all larval instars of S. exigua as hosts. The host distribution on potted plants in the large arena was manipulated to produce the spatial aggregation in L1～L2 and dispersed distributions in L3～L5, based on the spatial distributions in the field. In the large arena the parasitoid performed more encountering and rejecting acts toward young host larvae (L1～L2) than toward old host larvae (L3～L5), but in the small cage the above pattern reversed. The host-handling time was significantly longer in the large cage than in the small for each instar host, and increased linearly with host instars both in the large and small cages. The parasitoids in the small cage resumed attacks on earlier instar larvae (653.17s) in a longer interval compared to attacks on later instar larvae (171.32s), whereas the reverse was observed in the large cage. The earlier instar larvae (L1～L2) were parasitized at higher rates in the large cage (23.24～38.54%) than in the small cage (7.88～21.43%), but later instar larvae (L4) were parasitized more than in the small cage (34.65%) compared to the counterparts in the large cage (16.86%). Our studies suggest that space where parasitoid behaviors are observed have major impacts on their host selection behaviors.6. Meteorus pulchricornis was observed in a wind tunnel to investigate effects on behavioral responses, as affected by different experiences from immature stage to adult emergence and from oviposition while searching host larvae of Spodoptera exigua. The result showed an obvious effect of food plants for host larvae in which immature development and adult emergence were accomplished. Soybean plant exercised significant influence on the behavioral response of naive parasitoids, compared to the other testing plants, cotton and Chinese cabbage. For the parasitoids with an experience of oviposition once while searching hosts, the effect was contingent on plant species that the host larvae fed on. A significant response was performed to soybean-and Chinese cabbage-host larvae complexes. For those with experiences of oviposition twice on different plants, the follow up behavioral response was dependent both on plant species and their sequence experienced. When the oviposition experience happened between soybean and Chinese cabbage, soybean-host larvae complex was always preferred regardless of the sequence experienced. But when the experience occurred between soybean and cotton, the parasitoid only favored soybean-host larvae complex that was recently experienced. When the oviposition experience was between cotton and Chinese cabbage, the parasitoid only showed significant response to Chinese cabbage-host larvae complex that was recently experienced. The results suggest that both experiences from immature development and adult emergence site and those from oviposition can have effects on follow up behavioral responses, but these effects are stringent on plant species on which host larvae fed.