Effects of the insecticide thiamethoxam on Scaptotrigona postica Latreille, 1807 (Hymenoptera, Meliponina): determination of the average lethal concentration and analysis of enzyme activity

Abstract

Bees represent a highly diverse group, more than 20,000 species are described worldwide. In addition, they are considered one of the main pollinating insects in natural ecosystems or agricultural cultures, thus they are responsible for the maintenance of diverse ecosystems and for the realization of ecosystem services very important for humanity. Despite this, in recent years there has been a decline in the population of these pollinators and one of the factors that have stood out is the indiscriminate use of pesticides. In Brazil, the insecticide thiamethoxam has been used on a large scale, and besides presenting systemic characteristics it is also a neonicotinoid, that is, it acts mainly on the insects' brains. Although they are not targeted insects, bees are exposed in various ways to insecticides applied in the field. Thus, toxicity tests and risk assessments for pollinators seek to understand the extent of these effects and evaluate the use of insecticides, with Apis mellifera being used worldwide as a model for them. However, several questions were raised by IBAMA as to whether this is the best species to represent stingless bees in Brazil, in addition to highlighting the lack of study with them. Thus, the objective of this study is to determine the Average Lethal Concentration (CL 50) for the species Scaptotrigona postica using the insecticide thiamethoxam. In addition, using the CL 50 to understand the effects of two sublethal concentrations in the brain and intestine of bees, as well as their survival time (Mean Lethal Time - TL 50) when exposed to these concentrations. Finally, verify at the enzymatic level what effects are caused on the brain and intestine of bees, using respectively the enzyme that helps the cholinergic synapses (Acetylcholinesterase) and those responsible for detoxification (Carboxylesterase ¿ and Glutathione S-Transferase). Thus, such approaches seek to understand the effects of the insecticide thiamethoxam on the species S. postica and also to understand knowledge gaps about the species, generating knowledge that can be used in future risk assessments. (AU)