Effects Of Supplementary Food And Host Density On Foraging Behaviour And Functional Responses Of Meteorus Pulchricornis (Hymenoptera: Braconidae)

Hosts are distributed in discrete patches in the wild. The host patch foraging behavior is closely related with the population dynamics. Many adult parasitoids could feed directly or indirectly on plants in the field with the sugar resource ascarbohydrate meals are important for adult maintenance and longevity so that fecundity can be more realized. The working hypothesis for this study was that supplementary foods have effects on foraging efficiency and selection for host patches in parasiotids. According to this hypothesis, it was predicted that supplementary foods will have significant effects on foraging and residence time on host patches. To test this hypothesis, experiments were conducted to observe foraging behaviors of Meteorus pulchricornis (Wesmael) both in a clear cage in the lab and a large walk-in cage in the outdoor. Trials were also made outdoor to assess effects of supplementary foods on its functional responses.1. Effects of supplementary foods and host density on foraging behaviors of Meteorus pulchricornis—Lab trialsExperiments were conducted to evaluate effects of supplementary foods (no food, only water, and 30% g·L-1 sugar solution) and host density on foraging efficiency and parasitization selection behavior of Meteorus pulchricornis for Spodoptera litura larvae. Results indicated that:(i) host density had significant effects on foraging efficiency and selection for host patches with an obvious preference for high host-density patches. (ii) The supplementary foods tested did not effect foraging time, and thus had no significant influence on foraging efficiency. But the foods had influence on parasitism, which was significant when the paired-patch of 5 and 15 larvae per leaf was exposed to parasitism. (iii) As the host density and the number of oviposition increase, parasitoids tend to continue foraging on patches. The interaction of the two factors produced a positive effect on the patch-leaving tendency. Feeding 30% sugar liquid produced a positive effect on the patch-leaving tendency, but feeding water had no such an effect.2. Effects of supplementary foods and host density on foraging behaviors of Meteorus pulchricorni—utdoor trialsA semi-field experiment was conducted in an outdoor cage (2.5×2.5×1.8) with 15 potted soybean plants. Foraging behaviors of parasitoids with different supplementary food treatments were observed from 8:00 am to 16:00 pm. The Cox proportional hazard model was fitted and modelling results indicated that:(i) compared with water-feeding parasitoids, the parasitoids feeding 30% sugar liquid had a positive effect on patch-leaving tendency; (ii) the residence time on patches was decreased with host density, andthe cumulative hazard of leaving 10-larvae patch was 1.1 times greater than that of leaving 5 larvae patch; (iii) ovipositions had a negative effect on the patch-leaving tendency, where two ovipositions made parasitoids run less hazard of leaving the patch by 34.5% than one oviposition; (iv) interaction of supplementary foods and host density produced a negative effect on the patch-leaving tendency, where as the host density increased the cumulative hazard of leaving host patches decreased by 9.4 percent in parasitoids fed with sugar food compared to those fed with water; (v)supplementary foods had no significant effect on parasitism rates, but host density did affect parasitism rate by a negative correlation, where an increase of 5 larvae per patch made parasitism risk decrease by 7.1% while one minute longer on patches would increased parasitism risk by 0.9%.3. Effects of supplementary foods on functional responsesA semi-field experiment was conducted in an outdoor cage (2.5×2.5×1.8). Parasitism behaviors of parasitoids with different supplementary food treatments were observed from 8:00 am to 16:00 pm. There were six density levels ranging from 5 to 30 larvae per plant. The results showed that:(i) on five consecutive days the number of parasitism increased with the host density, with an increase of 5 larvae plant associated with a gain of 2.2 larvae parasitized; (ii) the number of parasitism decreased with time elapsed, with a decrease of 0.63 on average with extending one more day; (iii) there was a significant interaction bewtween host density and time elapsed on the number of parasitism, with a decrease of 3% with increase of both host density and time elapsed; (iv) there was an interaction between supplimentary foods and host density, with a 6% decrease in the number of parasitism by parasitoids fed with the sugar food with an increase of 5 larvae per plant compared to parasitoids fed with only water; (v) there was a significant interaction between supplimentary foods and the time elapsed after release, with the number of parasitized hosts increasing by 5% with an one-day increse in the time elasped in parasitoids fed with sugar foods as comapred to parasitoids with only water.