Sublethal effects of a spiromesifen and abamectin combination on Tetranychus urticae (Acari: Tetranychidae) and its predators Phytoseiulus persimilis and Amblyseius swirskii (Acari: Phytoseiiidae).

The two-spotted spider mite, Tetranychus urticae Koch (TSSM), is an important cosmopolitan pest of agricultural crops that is often managed in greenhouses by augmentation of predatory mites in combination with acaricides. Here we examined the transgenerational effects of low lethal concentrations of a widely-used acaricide, Oberon Speed® (a combination of spiromesifen and abamectin), on the life history traits and population growth of T. urticae and two of its predators, Phytoseiulus persimilis Athias-Henriot and Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae). The concentrations employed corresponded to the LC₁₀, LC₂₀ and LC₃₀ values estimated for TSSM protonymphs 48 h post-exposure in a topical bioassay, which yielded an LC₅₀ value of 207.2 ppm. Parental exposure of TSSM to all three low concentrations increased the total developmental time of progeny; both the LC₂₀ and LC₃₀ treatments reduced adult longevity and number of oviposition days, but only the LC₃₀ treatment increased the preoviposition period. Similarly, both the LC₂₀ and LC₃₀ treatments significantly reduced life table parameters (r, R₀, λ, and GRR), and increased generation time (T) and population doubling time (DT). Although maternal exposure to the acaricide had various impacts on progeny life history, A. swirskii was less affected than P. persimilis, suggesting the former species would be more compatible for integration with Oberon Speed® for control of T. urticae in greenhouse vegetable production.