Toxicity of novel neurotoxic insecticides on Tetranychus urticae and various phytophagous and predatory mite species.

Tetranychus urticae Koch (Acari: Tetranychidae) is a widespread pest that causes significant crop losses. Although acaricides are commonly used for its control, the development of resistance often leads to control failures under field conditions. Therefore, there is a constant need for new compounds with novel modes of action. Novel neurotoxic insecticides targeting γ-aminobutyric acid (GABA) receptors, such as isoxazolines and meta-diamides, represent one of the most recent classes of insecticides. However, their toxicity to T. urticae, other tetranychid mites, and predatory mites remains poorly understood. The isoxazoline insecticides fluralaner and isocycloseram showed very high toxicity to all T. urticae populations, with LC values ranging from 0.53 to 2.64 mg a.i./L and 0.04 to 0.26 mg a.i./L, respectively. Isocycloseram also caused 100% mortality in two other phytophagous mite species, Eutetranychus orientalis and Bryobia rubrioculus, at field application rates (30 mg a.i./L). In contrast, the meta-diamide broflanilide exhibited no toxicity against any of the tested phytophagous mites at the recommended field rate (20 mg a.i./L) and even at very high concentrations (5000 mg a.i./L), the mortality rate remained below 65% in all T. urticae populations except one. On the other hand, both isocycloseram and broflanilide, at their field rates, exhibited strong side effects ‒causing 100% mortality‒ on three predatory mite species: Phytoseiulus persimilis, Neoseiulus californicus, and Amblyseius swirskii. These findings highlight the potential of novel insecticides for mite control, while also emphasizing the importance of evaluating their non-target effects to support the development of sustainable pest management strategies.