Ultrastructure of the excretory organs of Bombus morio (Hymenoptera: Bombini): bee without rectal pads.

Bumblebees need to keep bodily homeostasis and for that have an efficient system of excretion formed by the Malpighian tubules, ileum, and rectum. We analyzed the excretory organs of Bombus morio, a bee without rectal pads. In addition, we analyzed the rectal epithelium of Melipona quadrifasciata anthidioides which has rectal pads. The Malpighian tubules exhibited two cell types and the ileum four types. However, comparative analysis of the rectum showed that only cells of the anterior region of the rectal epithelium of B. morio are structurally distinct. We suggest that cells of the Malpighian tubules of B. morio have an excretory feature and that cells of ileum have different functions, such as ion absorption and water, organic compound, and protein secretion. In addition, only the anterior region of the rectum of B. morio showed characteristic absorption. We suggest that Malpighian tubules participate in the excretion of solutes and that the ileum and rectal epithelium are responsible for homeostasis of water and solutes, compensating for the absence of rectal papillae. These results contribute to our understanding of the morphophysiology of the excretory organs of bees without rectal pads.