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.