The efficacy of biological control of Greenhouse whitefly ( Trialeurodes vaporariorum Westwood (1856) (Hemiptera: Aleyrodidae) by three natural enemies, Encarsia formosa Gahan (1924), Eretmocerus warrae Naumann & Schmidt (2000) (Hymenoptera: Aphelinidae) and Nesidiocoris tenuis Reuter (1895) (Hemiptera: Miridae), may be reduced by interactions between the species. I quantified host discrimination between the parasitoids through examination of multiparasitism (interspecific), superparasitism (intraspecific), and selfsuperparasitism (on own parasitism). The choice to host feed increases adult resources, whilst reducing oviposition resources. Host feeding contributes to whitefly control, but may destructively interfere with parasitoid population sizes. I report the level of host feeding and feeding preferences on parasitized and nonparasitized nymphs by the parasitoids. Comparative control by the two parasitoids, separately and together, is presented to determine if multiple or single introductions are more effective to achieve control. Feeding preferences by the omnivorous predator, N. tenuis, were analysed for potential interference on the establishment of En. formosa.

Laboratory choice experiments were conducted, using all parasitoid combinations (pairs of interspecifics, conspecifics, or the same parasitoid), where females had to choose between nonparasitized or parasitized whitefly nymphs, with treatments of a delay between the first and second parasitoids of 0 or 1 hr, or 1 day. All combinations showed the ability to host discriminate, and a preference for feeding and ovipositing on nonparasitized whitefly nymphs. Multiparasitism occurred in 19%, superparasitism in 7% and self-superparasitism in 4% of ovipositions by the parasitoids. Laboratory choice tests were conducted using N. tenuis, with a choice between parasitized or nonparasitized whitefly nymphs or pupae. These tests showed no preference between feeding on parasitized or nonparasitized whitefly nymphs, indicating N. tenuis may impact on En. formosa establishment. Caged tomato plants, in a greenhouse, were inoculated with whitefly; parasitoids were then released into the cages using a full factorial design, with four replicates of all treatments. All combinations of parasitoids decreased whitefly numbers relative to control, with no significant difference between the treatments. This demonstrates that En. formosa and Er. warrae are compatible as biological control agents in multiple introductions.

Food webs map feeding interactions among species, providing a valuable tool for understanding and predicting community dynamics. Using species' body sizes is a promising avenue for parameterizing food-web models, but such approaches have not yet been able to fully recover observed community dynamics. Such discrepancies suggest that traits other than body size also play important roles. For example, differences in species' use of microhabitat or non-consumptive effects of intraguild predators may affect dynamics in ways not captured by body size. In Laubmeier et al. (2018), we developed a dynamic food-web model incorporating microhabitat and non-consumptive predator effects in addition to body size, and used simulations to suggest an optimal sampling design of a mesocosm experiment to test the model. Here, we perform the mesocosm experiment to generate empirical time-series of insect herbivore and predator abundance dynamics. We minimize least squares error between the model and time-series to determine parameter values of four alternative models, which differ in terms of including vs excluding microhabitat use and non-consumptive predator-predator effects. We use both statistical and expert-knowledge criteria to compare the models and find including both microhabitat use and non-consumptive predator-predator effects best explains observed aphid and predator population dynamics, followed by the model including microhabitat alone. This ranking suggests that microhabitat plays a larger role in driving population dynamics than non-consumptive predator-predator effects, although both are clearly important. Our results illustrate the importance of additional traits alongside body size in driving trophic interactions. They also point to the need to consider trophic interactions and population dynamics in a wider community context, where non-trophic impacts can dramatically modify the interplay between multiple predators and prey. Overall, we demonstrate the potential for utilizing traits beyond body size to improve trait-based models and the value of iterative cycling between theory, data and experiment to hone current insights into how traits affect food-web dynamics.