Riscos da exposição crônica a resíduos de clorpirifós para operárias imaturas e adultas de abelha sem ferrão Scaptotrigona bipunctata

Abstract

RISKS OF CHRONIC EXPOSURE TO CHLORPYRIFOS RESIDUES ON IMMATURE AND ADULT WORKERS OF STINGLESS BEES The growing increase in the use of pesticides in agricultural ecosystems puts the pollinator populations at risk. Among these products, residues of the insecticide-acaricide chlorpyrifos (organophosphorus) are detected in the food resources collected by bees. Thus, assessment of the toxicological response resulting from exposure to this insecticideacaricide is essential to elucidate the action of this product on pollinators. Therefore, the present study evaluated the effects of chronic exposure to environmentally relevant concentrations of chlorpyrifos (equivalent to the residues found in pollen and honey) on the (1) larval development of worker bees rearing in vitro and on (2) adult worker stingless bees Scaptotrigona bipunctata. In order to carry out the tests, increasing concentrations of chlorpyrifos were added to the larval food (0.46 ng a.i./μL diet, 0.92 ng a.i./μL diet and 1.8 ng a.i./μL diet) provided to the immature, and a diet with no added insecticide was used as a negative control.The individuals were monitored daily until adult emergence and the survival, development time and morphometric characteristics of the newly emerged adults were evaluated. Sublethal concentrations of chlorpyrifos diluted in sucrose solution (0.011 ng a.i./μL diet, 0.056 ng a.i./μL diet and 0.112 ng a.i./μL diet - values representing 0.1, 0.5 and 1% of the LC50 for S. bipunctata) were chronically used in the feeding of the bees so that the tests could be performed in the adult phase. The first exposure to the insecticide was conducted without interruption until 100% mortality was reached for the exposed individuals in order to assess the survival rate and food consumption. For the other analyzes, the bees were fed for 27 days (survival time), then the walking behavior, enzymes activity acetylcholinesterase (AChE), superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferases (GST), in addition to thiobarbituric acid (TBARS) levels were evaluated. Possible ultrastructural changes in the midgut and in the Malpighian tubules of bees were also evaluated. As a result, it was observed that the larvae exposure to chlorpyrifos reduced survival rates significantly, but did not alter the development time of the immature. In addition, exposure to the insecticide reduced the size and body mass of newly emerged adults, and also caused a reduction in the alar area. Regarding bees exposed during adulthood, the intake of chlorpyrifos did not affect the survival rate and food consumption. After 27 days of exposure to the insecticide, changes in AChE activity were not observed, but the locomotor behavior was substantially impaired. Furthermore, extended exposure to chlorpyrifos resulted in decreased activity levels of the antioxidant enzymes SOD and CAT, and biotransformation enzyme GST. TBARS levels were also significantly reduced. The cells of the midgut of bees exposed to chlorpyrifos did not show relevant ultrastructural changes. However, ingestion of the insecticide caused changes in the epithelium of Malpighian tubules. In view of the results presented, we consider that exposure to chlorpyrifos residues represents a risk for both the immature and adults of the stingless bee S. bipunctata. The changes observed in the physiology and behavior of bees can compromise the homeostasis of the colonies, thus contributing to the decline of their populations. This study contributes to a better understanding of the effects of chronic exposure to environmentally relevant concentrations of chlorpyrifos and the results presented here may have implications for other species of bees.