Prophylactic Releases of Predatory Mites to Protect Ruellia simplex from the Eriophyoid Mite Acalitus simplex

The eriophyoid mite Acalitus simplex induces the formation of open galls (erinea) on Ruellia simplex plants in ornamental landscapes, compromising their aesthetic value. Management of A. simplex currently involves implementation of chemical and mechanical methods, while biological control remains largely unexplored. This study aimed to assess the potential of two commercially available predator mite species, Amblyseius andersoni and Am. swirskii, and three naturally occurring predator mite species, Am. adhatodae, Phytoseius woodburyi, and Am. largoensis. Predator efficiency was first evaluated under laboratory conditions by measuring predator oviposition when fed ad libitum on Ac. simplex. Amblyseius swirskii laid significantly more eggs than Am. andersoni, whereas Am. adhatodae and Am. largoensis laid slightly more eggs than P. woodburyi. Amblyseius swirskii and Am. adhatodae were further evaluated under greenhouse conditions using two release approaches: i) curative, after erinea formation, and ii) prophylactic, before erinea formation. Neither predator prevented new erinea formation on already infested plants; however, despite limited development of hyaline erinea, predators were efficient in preventing infestations on previously uninfested plants. In the curative approach, A. swirskii and A. adhatodae successfully established on the plants but did not reduce Ac. simplex population density. In the prophylactic approach, predators substantially reduced Ac. simplex populations, but the low recovery of predator eggs indicated lack of establishment. Our results suggest that if Am. swirskii and Am. adhatodae are established on R. simplex plants prior to Ac. simplex infestation, they can effectively protect plants from the pest.