Effects of Intraguild Predation and Interspecific Competititon among Biological Control Agents in Augmentative Biological Control in Greenhouses

Two natural enemy species are frequently released simultaneously to control one pest species in augmentative biological control in greenhouses. Intraguild predation (IGP) and interspecific competition between natural enemies might affect the biological control. IGP occurs between two parasitoids, between one parasitoid and one predator, and between two predators. Although unidirectional IGP has been found in many studies about IGP between natural enemies used in the biological control of greenhouse pests, no significant effects of IGP on biological control have been recognized. On tomatoes in greenhouses, Liriomyza trifolii is usually controlled by the combined release of Dacnusa sibirica and Diglyphus isaea. Trialeurodes vaporariorum, another pest of greenhouse tomatoes, can be controlled by the combined use of Encarsia formosa and Eretmocerus eremicus. Simulation models incorporating IGP or interspecific competition between these parasitoid species have been constructed for evaluating biological control using two parasitoid species. These simulation models suggested no significant negative effects of IGP or interspecific interactions between two parasitoids on biological control.