Effect of a 110 ppb mercury exposition on neotropical bumble bee workers, Bombus atratus: in situ localization of Hsp70 and Hsp90 and general morphological changes of hepato-nephrocitic cells

Abstract

We analyzed the effect of mercury (Hg) on the hepato-nephrocitic system (HNS) of Bombus atratus workers exposed to an estimated concentration similar to that found in honey stores of neotropical bees (110 ppb). The bees were divided into control and experimental groups. A solid mixture of honey, pollen and organic soy was offered to both experimental groups, ad libitum. The control group received distilled water and the exposed group received a 110 µg.L−1 (110 ppb) Hg solution. After 48 h of exposure, the bees were cryo-anesthetized, and the dorsal vessel was dissected directly in 4% paraformaldehyde. The samples were prepared for routine morphological analysis (HE), fluorescent histochemical staining (Acridine Orange and F-actin + DAPI), and in situ immunohistochemical labeling (Hsp70 and Hsp90). Our results showed that both the trophocytes and oenocytes of bees exposed to mercury exhibited chromatin damages. The Hg exposure also induced trophocytes deactivation of the nucleus-cytoplasm exchange as a result of branched contour loss of the nuclei. The pericardial cells were predominantly found at stage IV with pyknotic nuclei. Although the fluorescence intensity of both Hsp70 and Hsp90 was reduced in the exposed group compared to the control group, there was an indication of misfolded proteins. In conclusion, our results showed that the concentration of 110 µg.L−1Hg, which can be found in the honey stores of B. atratus colonies, has severely damaged the HNS of B. atratus workers. These effects can trigger major damage to their populations, contributing to bee declines in natural environments worldwide.