Pre-parasitism host treatment with broflanilide: lethal and sublethal effects on Trichogramma evanescens

Broflanilide has recently emerged as a highly effective tool for managing a diverse array of pest insects, including both chewing and sucking species. However, its compatibility with natural enemies—a crucial component of Integrated Pest Management strategies—remains underexplored. Therefore, there is an urgent need to evaluate its selectivity towards natural enemies, particularly the generalist egg parasitoid Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae). This study aims to investigate the lethal and sublethal effects of host eggs being treated with broflanilide on T. evanescens. To determine the median lethal concentrations, a series of concentrations, 0.0, 0.1, 0.5, 1, 5, 7, and 10 mg.ai.L⁻¹, were employed to cause mortality. The median lethal concentrations were determined as an LC₂₅ = 0.3 mg.ai.L^-1 and an LC₅₀ = 1.1 mg.ai.L^-1. The F0 parasitism performance and the F1 emergence ratio were unaffected by these concentrations. Subsequently, further experiments assessed whether the parasitoids could distinguish between untreated host eggs and those treated with sublethal broflanilide concentrations (LC₂₅ and LC₅₀). The parasitism preference index showed that the parasitoids could not distinguish between the insecticide-treated and untreated host eggs in two-choice experiments. These findings offer preliminary insights into the toxicity of broflanilide to T. evanescens when the host eggs are treated prior to parasitism. Ongoing research aims to refine these results and offer more conclusive and practical recommendations.