Oral acute toxicity and impact of neonicotinoids on Apis mellifera L. and Scaptotrigona postica Latreille (Hymenoptera: Apidae).

Wild and managed bees are essential for crop pollination and food production. However, the widespread use of insecticides such as neonicotinoids may affect the survival, development, behavior, and maintenance of bee colonies. Therefore, in this study we evaluated the impacts of three neonicotinoid insecticides on the survival and walking abilities of the Africanized honeybee A. mellifera and stingless bee S. postica. A. mellifera was more susceptible than S. postica to all neonicotinoids tested. The median lethal concentrations LC50 values estimated for acetamiprid, imidacloprid, and thiacloprid were 189.62, 22.78, and 142.31 ng µL-1 of diet for A. mellifera, and 475.94, 89.11, and 218.21 ng µL-1 of diet for S. postica, respectively. All tested neonicotinoids affected the speed, distance traveled, duration and frequency of resting, and continuous mobility of both bee species. The results showed that in spite of the different susceptibility to compounds with cyano and nitro radicals, the behavioral variables showed different levels of commitment according to the molecule insecticide and bee species. These results contribute not only to the understanding of the effects of neonicotinoid insecticides on A. mellifera and S. postica, but also to help in the development of protocols that aim to reduce the impact of these insecticides in Neotropical environments.

Impact of fipronil on the mushroom bodies of the stingless bee Scaptotrigona postica.

BACKGROUND: Studies on stingless bees are scarce, and little is known about these insects, especially regarding the effects of contamination by neurotoxic insecticides, which can cause damage to important structures of the insect brain. This study evaluated the morphological changes in the intrinsic neurons of the protocerebral mushroom bodies (Kenyon cells) of the stingless bee Scaptotrigona postica after exposure to different doses of fipronil, using light microscopy and transmission electron microscopy. This region of the brain was selected for analysis because of its importance as a sensory integration centre. RESULTS: In both oral and topical treatments, Kenyon cells presented pyknotic profiles, suggesting cell death. Statistical analysis showed significant differences among doses and exposure times. Transmission electron microscopy revealed changes in the nucleus and cellular organelles. Depending on the dose, the characteristics observed suggested apoptotosis or necrosis. CONCLUSION: This study demonstrates the toxic effects of fipronil. An increase in the number of pyknotic profiles of Kenyon cells of mushroom bodies was observed even at the sublethal doses of 0.27 ng AI bee(-1) and 0.24 ng AI µL(-1) in the topical and oral treatments respectively. Also, differences in the number of pyknotic profiles were dose and time dependent.