Toxicity of Spirodiclofen to the Predatory Mite, Amblyseius womersleyi (Acari: Phytoseiidae), and its Prey, Tetranychus urticae (Acari: Tetranychidae)

The relative toxicity of spirodiclofen to the predatory mite, Amblyseius womersleyi Schicha (Acari: Phytoseiidae), and its prey, Tetranychus urticae Koch (Acari: Tetranychidae), was evaluated in laboratory bioassays. Spirodiclofen was much less toxic to A. womersleyi than to T. urticae. Although the survival rate of adult females of A. womersleyi tended to decrease with increasing concentrations of spirodiclofen, 62–96% of the predators survived at concentrations of 22.5–180 ppm. Reproduction of adult female predators was only significantly affected at high concentrations (90 and 180 ppm). Spirodiclofen did not affect the hatch of A. womersleyi eggs at any concentration tested. Survival of immature predators was significantly decreased with increasing spirodiclofen concentration, however, 30–78% of immature predators reached adulthood at 22.5–45 ppm. Adult female predators survived on a diet of spider mites treated with spirodiclofen, and their fecundity was not significantly affected. Moreover, immature predators developed normally on prey treated with spirodiclofen. Spirodiclofen at selective sublethal concentrations (i.e., 22.5–45 ppm) could be of value in adjusting the prey/predator ratio in integrated management of T. urticae.