Effects of sublethal doses of pesticides on the Scaptotrigona postica (Latreille, 1807) key organs

Scaptotrigona postica, is a native stingless bee, important in the pollination of native and agricultural áreas in Brazil. The inappropriate use of pesticides is one of the main causes of their population decrease. The exposure to the sublethal doses can cause morphological changes and affect their immune system, leading them to death. Thus, this work aimed to evaluate and compare the morphological changes caused in the intestine and in the Malpighian tubules using a semi-quantitative analysis described by Grella et al., (2019). For that, forages of S. postica were collected and exposed to sublethal concentrations of the insecticide dimethoate (0.04392 ng/μL) and the fungicide azoxystrobin (0.060 ng/μL). Five experimental groups were analyzed for each pesticide, being: (1) control (fed only with syrup-50%); acute exposure to pesticides to (2) azoxystrobin and (3) dimethoate (fed for 1 day); and chronic exposure to (4) azoxystrobin and (5) dimethoate  (fed for 10 days). After these periods, the organs were collected, sectioned, and stained by Hematoxylin Eosin technique. The analyzed changes were: loss of cytoplasmic material, loss of brush border, elimination of cells to the lumen, loss of regenerative cell nests, cell swelling, cells with pycnotic nuclei, apocrine secretion and spherocrystals. After analyzing the results obtained, we observed that both forms of exposure were able to cause changes in the parameters mentioned. However, chronic exposure caused greater damage. Sublethal concentrations of these pesticides cause morphological changes in important organs involved in the metabolic pathway and can affect the individual answer to toxicity.