Efeito residual do tiametoxam em folhas de meloeiro sobre Apis mellifera.

Abstract

Conciliating the application of insecticides for pest management and the conservation of the honey bee Apis mellifera (Hymenoptera: Apidae) is one of the greatest challenges for melon (Cucumis melo) producers. Therefore, it is essential to understand the toxicity of insecticides on bees. The insecticide Thiamethoxam is considered highly toxic to A. mellifera at registered doses for use on melon plants. However, there is still limited information on the residual effect of this insecticide over time after spraying. Therefore, the objective of this study was to evaluate the residual effect of Thiamethoxam on A. mellifera in relation to time after spraying on melon leaves. The experiment was conducted in the Entomology Laboratory of the Center for Agri- cultural Sciences and Technology (CCTA) at the Federal University of Campina Grande (UFCG), Pombal Campus, Paraíba, Brazil. The bioassay corresponding to residual contact mode was carried out on melon leaves, followed by an evaluation of the bees' flight capacity. The bioassay was conducted in a completely randomized design, with a 3 X 5 factorial scheme, consisting of two doses of the insecticide Thiamethoxam (0.03 g a.i./L and 0.3 g a.i./L), a con- trol (distilled water), and five exposure times after product application (1, 2, 3, 24, and 48 hours), with five repetitions, each experimental unit consisting of 10 adult bees. Mortality and behavior (e.g. prostration, paralysis, tremors) of the bees were evaluated at 1, 2, 3, 4, 5, 6, 12, and 24 hours after exposure. The flight capacity was assessed for all bees that survived after exposure to the insecticide. The insecticide Thiamethoxam caused mortality between 75% and 100%, with the highest percentages observed for the 0.03 g active ingredient per liter dose at 1 hour after spraying and for the 0.3 g active ingredient per liter dose at 1 and 2 hours after spra- ying. After 3, 24, and 48 hours of spraying with the 0.03 g active ingredient per liter dosage, the Median Lethal Time (TL50) was 13.3 hours. In the evaluations at 1 and 2 hours after spra- ying, using the 0.03 g active ingredient per liter dosage, and 48 hours after spraying with the 0.3 g active ingredient per liter dosage, the TL50 was 7.3 hours. In the evaluations at 1, 2, 3, and 24 hours after application, with the 0.3 g active ingredient per liter dosage, the TL50 was 3.5 hours, the shortest lethal time among all the evaluated doses. A significant difference was observed in the flight capacity of bees exposed to Thiamethoxam compared to the control group. Regardless of the dose, Thiamethoxam was highly harmful through residual exposure at 1, 2, 3, 24, and 48 hours after spraying, at the dosages of 0.03 g active ingredient per liter and 0.3 g active ingredient per liter, on adult A. mellifera.