Endocrine cells in the midgut of bees (Hymenoptera: Apoidea) with different levels of sociability

Abstract

Bees are important models to study the physiological role of endocrine cells. These cells produce hormones and may be open or closed cells depending on whether they have direct or indirect contact with the gut lumen, respectively. Food is digested and absorbed in the insect midgut. The objective of this study was to identify endocrine cells in the midgut of bees of different levels of sociability to understand the function of these cells. The midgut of Centris fuscata, Epicharis flava, Euglossa imperialis, Eulaema nigrita, Frieseomelitta varia, Megachile rava, and Melipona quadrifasciata anthidioides (Hymenoptera: Apoidea) was subjected to immunohistochemistry test for FMRF-amide. The midguts of E. imperialis, E. nigrita, and M. rava showed closed FMRFamide-positive endocrine cells, and those of E. flava, F. varia, and M. quadrifasciata anthidioides showed open cells. The greater number of open FMRFamide-positive cells suggest that this peptide probably regulates the synthesis of digestive enzymes without cell receptor and signal transductors, while closed FMRFamide-positive cells suggest that these peptides may play a role in regulating peristaltic movements of digestive tract. Presence of FMRFamide-positive cells in the bees, regardless of their sociability level, reflects the phylogenetic conservation of the peptide FMRFamide family in these bees.