Because predators may interfere with each other, an important step towards the implementation of successful release of multiple predators in biocontrol programs requires resolving how predators respond to the presence of heterospecific competitors. Several species of predatory mites are important biocontrol agents and the species Phytoseiulus macropilis and Neoseiulus californicus are used to control the two-spotted spider mite, Tetranychus urticae, an important pest in agriculture worldwide. We investigated their compatibility showing that the two predators do not avoid plants on which the other species is present together with their common prey, and demonstrated that their oviposition rates are not affected by the presence of the other species. However, the distribution of the eggs on leaf discs was affected by the presence of the heterospecific predator. This behaviour might weaken possible interference between these two biocontrol agents, which, in turn, may enable their persistence on plants and favour pest suppression. The increased joint use of several natural enemies for biological control highlights the importance of studies on predator-predator interactions.
Keywords: Augmentative biological control; Interspecific competition; Multiple predators; Phytoseiidae; Volatile chemical cues.