Comparative toxicity of spinetoram to the greenhouse whitefly and its parasitoid Encarsia formosa

Abstract: The assessment of chemical toxicity towards target and non-target organisms is
required when Integrated Pest Management programs are adopted. Spinetoram, a semisynthetic analogue of the microbial-derived bioinsecticide spinosad, is widely used to control insect pest populations in agricultural crops. However, spinetoram toxicity towards the greenhouse whitefly Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae) and its successful biological control agent, the parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae), has been scarcely documented. We assessed the acute toxicity of spinetoram insecticide (25 % a.i.) to adults and nymphs of the whitefly, as well as to adult and pupal stage of the parasitoid in laboratory conditions. In all dose-response bioassays a Potter spray tower was used to apply the insecticide to tobacco leaves settled onto 1 % agar layer in ventilated Petri dishes. Adults of both pest and parasitoid were exposed for 48 h to dry residues, while whitefly nymphs and parasitoid pupae were directly sprayed with a series of spinetoram concentrations, covering a range of 10-90 % mortality. The following median Lethal Concentrations (LC50s) were estimated: 4.593 and 15.027 mg a.i./l for whitefly adults and nymphs, respectively, and 0.686 and 1.715 mg a.i./l for parasitoid adults and pupae,
respectively. The calculated selectivity ratio (LC50 parasitoid/ LC50 whitefly) indicated the nonselective nature of spinetoram towards both tested stages of the parasitoid. However, a more comprehensive risk-assessment for E. formosa involved in the integrated use of spinetoram insecticide within whitefly management requires further evaluation of the sublethal effects and greenhouse trials, aiming to highlight population-level responses.