Thiacloprid + deltamethrin against the cotton aphid and the parasitoid wasp Aphidius colemani: From lethal to sublethal population effects

The side effects of insecticides on non-target species are important to secure the intended effectiveness of pest management programmes. The cotton aphid Aphis gossypii is a frequent problem in industrial greenhouse cultivation, and insecticide and parasitoids are often used for crop protection. Among insecticides, mixtures are playing increasing roles in pest management in the greenhouse production system, as well as parasitoid use. The insecticide mixture thiacloprid + deltamethrin and the parasitoid wasp Aphidius colemani are the main agents used against the cotton aphid and are the focus of this study. Here, we report the effects of the thiacloprid + deltamethrin on A. gossypii and Ap. colemani. The low concentrations 2.79 g a.i/L (LC₁₀) and 7.28 g a.i/L (LC₃₀) compromised the life parameters of the aphid progeny and increased the development time at all juvenile stages. In addition, fecundity, longevity and other parameters (r, R₀ and T) were significantly impaired by thiacloprid + deltamethrin at both concentrations. The median lethal time estimate (LT₅₀) for Ap. colemani was 18.73 h; the parasitoid mortality was significant up to 24 h after application but decreased afterward. Regardless, the parasitoid life table parameters were also compromised by insecticide exposure, similarly to the parasitoid population growth and parasitism efficacy. These results demonstrate the effect of the insecticide mixture against A. gossypii, and the increased risk of its adverse impacts on the parasitoid Ap. colemani, which signals against their simultaneous application to control this pest species.