Predation by phytoseiid mites on Tetranychus lintearius (Acari: Tetranychidae), an established weed biological control agent of gorse (Ulex europaeus)

Development of trophic relationships among introduced biological control agents and native (or introduced) parasitoids, predators, or pathogens can interfere with successful establishment, spread, and ecological impact on the target pest. For the introduced weed biological control agent Tetranychus lintearius (Dufor), we assessed predator acquisition, the ability of these predators to survive and reproduce when held with the weed biological control agent, and their impacts on agent populations. Surveys of T. lintearius (spider mite) colonies demonstrated that this biological control agent of gorse, Ulex europaeus L., has acquired generalist and specialist feeding predatory mites in its adventive range but association alone is insufficient evidence to conclude that these mites are negatively affecting the weed biological control agent. Predation bioassays demonstrated that all predatory mites tested can feed, survive, and reproduce when held with T. lintearius lending evidence to the interference hypothesis. The number of spider mite colonies and volume of gorse foliage colonized were higher when the introduced predatory mite Phtyoseiulus persimilis Athias–Henriot was excluded from plots, indicating these mites are suppressing T. lintearius populations. We report the predation of T. lintearius by a complex of predatory mites that are routinely used for biological control of spider mites in agricultural systems.