Effect of Cadmium on Worker Ovary Morphology of Bombus morio (Hymenoptera: Bombini)

Abstract

Bees are valuable bioindicators, providing information regarding environmental conditions through different kinds of analyses. Therefore, the effect of cadmium on the morphology of ovaries of Bombus morio workers was used to study a concentration considered environmentally safe (1 ppb) in Brazil. Workers of the same estimated age exposed for 48 h to 1 ppb cadmium showed extensive morphological changes in the germarium and vitellarium compared with the control group. Bees exposed to cadmium showed death of or damage to entire vitellogenic follicles, with chromatin condensation and fragmentation of nurse cell nuclei. In the germarium, the intercellular bridge connecting the primary oocyte to the developing nurse cells was broken. The nurse cells formed a cluster of cells with compacted chromatin, detached from an isolated primary oocyte. In some cases, the cytoblasts were absent from the germarium, leaving an empty space surrounded by collapsed peritoneal sheaths. We further propose that such a hazardous impact of 1 ppb cadmium on the ovaries of B. morio workers is not only mainly due to cadmium itself as an endocrine disruptor, indirect oxidative stress promoter, cytoskeleton destabilizer and mutagenic trace metal, but by disruption of the trophocytes, where perivitelline space filled with eosinophil material in the control group, was totally empty in exposed bees, suggesting interruption of trophocyte vitellogenin production.