Toxicity of fluralaner against vegetable pests and its sublethal impact on a biocontrol predatory ladybeetle

Fluralaner, a systemic pesticide, was originally registered with the US Food and Drug Administration in 2014 under the trade name Bravecto for flea treatment for pets. As a GABA antagonist, the footprint of fluralaner has expended beyond medical and veterinary pests in recent years. In this study, we examined the acute toxicity of fluralaner against three pests of Henosepilachna vigintioctopunctata, Megalurothrips usitatus, and Phyllotreta striolata in the Solanaceae, Fabaceae, and Cruciferae families, respectively, and the sublethal impact of fluralaner on Propylaea japonica, a widely distributed predatory ladybeetle. Based on LC₅₀, fluralaner was effective against H. vigintioctopunctata (0.098 mg a.i. L⁻¹ for the second instar larvae), M. usitatus (0.134 mg a.i. L⁻¹ for adult females), and P. striolata (0.595 mg a.i. L⁻¹ for adults). For P. japonica, however, fluralaner was substantially less effective (1.177 mg a.i. L⁻¹ for the third instar larvae). Furthermore, the LC₁₀ and LC₃₀ of P. japonica were also consistently higher than the LC₅₀ of the three pests. In addition, we did not observe any significant impacts of fluralaner at LC₁₀ and LC₃₀ on the life history traits, including body weight, developmental time, pre-oviposition period, and fecundity of P. japonica. Based on our results from acute toxicities and sublethal impacts, fluralaner is effective against vegetable pests, while potentially friendly to P. japonica when employed as a biological control agent.