Morphology of the hypopharyngeal gland of the stingless bee Scaptotrigona postica (Apidae: Meliponini) and the effects of pesticides

Abstract

Bees play a crucial role in pollination but are exposed to various pesticides during nectar and pollen collection, which can impact their health and pollination efficiency. This study aimed to investigate morphological and histochemical changes in the hypopharyngeal glands of Scaptotrigona postica after exposure to three chemical compounds: glyphosate, fipronil, and Tween. Nurse bees of S. postica were divided into four experimental groups and fed with sucrose syrup containing the compounds for 24 h. After the exposure period, the hypopharyngeal glands were analyzed for morphology using light microscopy and transmission electron microscopy. The hypopharyngeal glands of S. postica exhibited a tubuloacinar structure, with unicellular acini approximately 54 µm in diameter. Exposure to fipronil resulted in changes in the organization of the rough endoplasmic reticulum (RER) and increased area and sphericity of the acini compared to all other groups, as well as a higher presence of proteins in the cytoplasm compared to other pesticides, potentially due to increased food consumption. Bees exposed to glyphosate showed alterations in the mitochondria compared to all groups. The Tween group did not exhibit significant changes in cellular ultrastructure, only a smaller area and sphericity compared to the control group. The hypopharyngeal glands are highly sensitive to pesticides and are efficient bioindicators. Significant changes in these glands can compromise the maintenance of the colony.