Atividade formicida de derivados de timol sobre operárias de Acromyrmex balzani.

Abstract

Leaf-cutting ants, Acromyrmex balzani, are important pests of forest and agricultural ecosystems. Chemical control is the most used method to control them, however, recent research highlights the anticidal potential of essential oils in controlling this pest. In this sense, thymol stands out for being one of the main constituents of several aromatic plants and for showing activity against insect pests. However, there is still no information on the effects of its derivatives on leaf-cutting ants. Thus, the objective of this work is to evaluate the toxicity of thymol, its derivatives and the insecticide deltamethrin on worker ants of A. balzani. To carry out the bioassays, worker ants were initially weighed to obtain the average mass of the insects. The treatments (thymol, thymil acetate, thymyl benzoate, thymyl chloroacetate, thymil ethyl, thymil methyl, thymil propionate, thymyl trichloroacetate and deltamethrin) were applied topically (1.0 μL) in the prothoracic region of each insect with the aid of a microsyringe, using preliminary doses of the compounds (1.0; 2.5; 5 μg of substance/mg of insect). In the control, only acetone was used. The experimental design was completely randomized with six replications. Each repetition is composed of seven ants of the same size, kept in Petri dishes, lined with filter paper and moistened with distilled water. Then, the plates containing the treated ants were kept in air conditioned rooms, where they remained until the evaluation, which was carried out 72 hours after setting up the bioassays. The data obtained show that the most toxic derivative to A. balzani was thymyl chloroacetate with an LD50 of 1.41 mg/g. Among the seven derivatives tested, thymyl benzoate was the one with the lowest toxicity (LD= 5.67 mg/g). Furthermore, thymol and its more (chloroacetate) and less (benzoate) toxic derivatives significantly reduced A. balzani survival, with TL50s of 15; 26; 32; 31 and 35; 73 hours, respectively. This research makes an important contribution with toxicological information on thymol derivatives on A. balzani workers that may contribute to the development and synthesis of new ant killers.