Toxicidade do extrato aquoso de Simarouba sp. em Plutella xylostella, Apis mellifera e Melipona quadrifasciata

Abstract

Botanical extracts are natural chemical products derived from plants, whose synergistic action of secondary metabolites can interfere with the biological characteristics of insect pests. Thus, they represent a promising alternative for the control of species resistant to synthetic insecticides, such as Plutella xylostella (Linnaeus, 1758) (Lepidoptera: Plutellidae). Commonly known as the diamondback moth, this species is one of the main lepidopteran pests of brassicas and stands out for its resistance to several registered active ingredients. Additionally, botanical extracts are known for their lower environmental persistence and, in general, lower risk to human health. However, the scarcity of information on their effects on non-target organisms, such as pollinators and natural enemies, hinders the safe application of botanical insecticides in crop areas. In this context, the objective of the present study was to evaluate the mode of action of the aqueous extract of Simarouba sp. (EAS), at different concentrations, on Plutella xylostella, with emphasis on alterations in the midgut (Chapter I), as well as to investigate the selectivity of the extract to Apis mellifera and Melipona quadrifasciata (Chapter II). For the histological analyses, second-instar larvae were exposed for 48 h to kale leaves (Brassica oleracea var. acephala) treated with the botanical extract at concentrations of 0.01%, 0.05%, 0.1%, 1%, 5%, and 10%, in addition to the control treatment, which consisted of distilled water. After exposure, caterpillars were randomly collected from each treatment for histological processing and evaluation. For the selectivity tests in bees, workers of A. mellifera and M. quadrifasciata were exposed to EAS at concentrations of 0.01% and 0.05% by oral and topical routes. Survival was evaluated over 96 h. Sublethal effects on locomotion were analyzed by video tracking using the EthoVision XT system. The highest concentrations of the aqueous extract of Simarouba sp. (10% and 5%) caused marked alterations in the midgut of P. xylostella, with impairment of the intestinal epithelium. The main alterations observed included cellular disorganization, presence of vacuoles, and protrusions and extrusions toward the lumen. In addition, at the highest concentrations, it was not possible to identify the presence of the peritrophic membrane, suggesting impairment of the structure responsible for protecting the intestinal epithelium. Regarding selectivity, in A. mellifera, EAS caused low impact on survival after oral exposure, with high survival throughout the evaluation period, whereas, after topical exposure, the concentration of 0.05% promoted mortality close to 50% at the end of 96 h. In M. quadrifasciata, the effects were more evident after oral exposure, in which EAS at 0.05% caused mortality of at least 50% of individuals at the end of 96 h, allowing the estimation of the LT50, whereas, after topical exposure, all treatments showed survival above 70%. Regarding locomotor activity, EAS altered the movement pattern in both species, mainly affecting mean speed, mean distance, and locomotion intensity. In M. quadrifasciata, it also caused resting periods, indicating absence of movement. In summary, our results demonstrate that the aqueous extract of Simarouba sp. promotes significant alterations in the midgut of P. xylostella, highlighting its potential as a promising alternative for the ecological management of insect pests. However, EAS also showed lethal and sublethal effects on bees, depending on the species, exposure route, and concentration, with 0.05% being more toxic than 0.01%. These findings indicate that, although botanical extracts have potential for pest control, they may also pose risks to non target organisms, such as pollinators, reinforcing the need to develop appropriate protocols for assessing the toxicity of plant-derived products.