Fitness For Parasitizing Hosts At Differnet Ages And Patch Foraging Behaviors At Predation Risk In Meteorus Pulchricornis (Hymneoptera:Braconidae)

Parasitoids are ideal model systems to study foraging and developmental strategy, as offspring fitness completely depends upon the female wasps to make adaptive oviposition decisions. Until now, most studies on developmental performances of offspring parasitoids in response to host ages use molting as a measure of age, but few utilize day to measure age and even less attention has been paid to reproductive performances. Though numerous studies on parasitoid foraging behaviors are done, less focuses have been put on predation risks that affect parasitoids during their foraging. The thesis aims to answer the questions: (1) How Meteorus pulchricornis development and reproduction performs in relation to Spodoptera litura larval day-based ages? (2) Do the presence of the predaceous bug Cyrtopeltis tenuis influence foraging behaviors of M. pulchricornis on host pathes? Main results and conclusions obtained from the study are summarized below.1. Developmental and reproductive performances of offspring parasitoids in response to host age at ovipositionIt is well established that medium aged host larvae are higher in quality than the two ends of host instar for fitness of solitary parasitizing parasitoids attacking lepidopteran larvae. The previous supporting studies are mostly conduced using larval instars as host treatments and putting little focus on reproductive performances of offspring parasitoids, leading to inaccurate and incomplete description of parasitoid fitness and host age at parasitism. This study manipulated S. litura larvae as host age treatment in days and examined both developmental and reproductive parameters of offspring M. pulchricornis. The results of this study showed that female M. pulchricornis performed more parasitism on medium aged hosts than on younger and older hosts at oviposition. Offspring developmental survival, adult body size and fecundity in number of eggs laid were greater in medium aged hosts as compared with those in younger and older hosts, confirming to the "dome-shaped" model.2. Indirect predation of M. pulchricornis via S. litura larvae by C. tenuisTo examine indirect predation of M. pulchricornis by C. tenuis through preying on S. litura host larvae, trials were first made to measure consumption potential of C. tenuis to different instars of healthy larvae, and then to compare predation selection between healthy and parasitized hosts at different instars. The results showed that C. tenuis consumed S. litura larvae at the 1st stadium by 13.8±0.55, but significantly less larvae at higher instars, and least for the 3rd instar larvae (0.5±0.17). In choice trials between healthy and parasitized hosts at the same instar, predatory bugs did not show preferences between the 2nd and 3rd instar host larvae, but did between the 1st instar, preferring the healthy larvae. In choice trial between healthy and parasitized hosts cross instars, predatory bugs did not perform preferences between the 2nd healthy and 3rd parasitized hosts, and between the 3rd healthy and 2nd parasitized hosts, but did between the 1st healthy and 2nd parasitized hosts, the 1st healthy and 3rd parasitized, the 1st parasitized and 2nd healthy, and the 1st parasitized and 3rd healthy hosts, respectively. These results suggest that the predatory bug may actually base prey body size to make predation decisions.3. Effects of predation risk on patch foraging behaviorWe tested three density treatments:5,10,30 larvae per leaf on a plant, with or without the presence of C. tenuis on patches. The result showed that the presence of the predator had a significant effect on the wasp in patch-time allocation. The cumulative tendency of leaving patches in the presence of predators was 14.68 times more than that without. The host density had no significant effects on the patch-residence time. The sting of ovipositors had significant effects on patch residence time. Each one more sting increased the patch-leaving tendency by 6.43 times. The resting time had a significant effect, increasing the leaving tendency by 1% with each second elapsed for resting. But proportion parasitized hosts did have significant influence on the wasp in patch-time allocation.