Toxicity of neonicotinoid insecticides to Neoseiulus californicus and Phytoseiulus macropilis (Acari: Phytoseiidae) and their impact on functional response to Tetranychus urticae (Acari: Tetranychidae)

Evaluations of possible impacts of insecticides on natural enemies are highly relevant in integrated pest management (IPM) programs. Because of the intensive use of neonicotinoid insecticides for controlling sucking pests, the objectives of this study were to evaluate the toxicity of these insecticides on the phytoseiid mites Neoseiulus californicus (McGregor) and Phytoseiulus macropilis (Banks) (Acari: Phytoseiidae) and their impact on the functional response to Tetranychus urticae Koch eggs. A residual-type bioassay was used to evaluate mortality of adult females of both predator mites exposed to acetamiprid (80 mg a.i./L), imidacloprid (280 mg a.i./L), and thiamethoxam (135 mg a.i./L). The impact of each insecticide on the functional response of the predators was carried out by spraying T. urticae eggs with insecticides at densities of 5, 10, 20, 40, 60, and 80 eggs per arena. All insecticides evaluated showed low toxicity on the adult females of both species. However, the insecticides differently affected the functional responses exhibited by N. californicus and P. macropilis. Although acetamiprid did not affect the predatory capacity of N. californicus, it was detrimental to the performance of P. macropilis from a density of 20 T. urticae eggs per arena. Imidacloprid changed the functional response parameters estimated for both species, with reductions of 55% and 87% relative to the peak consumption observed for N. californicus and P. macropilis, respectively. Thiamethoxam significantly reduced P. macropilis consumption from a density of 40 T. urticae eggs per arena. Therefore, the use of neonicotinoid insecticides should be evaluated carefully in IPM programs.