Dietary phytochemicals alter hypopharyngeal gland size in honey bee (Apis mellifera L.) workers

Authors: LASTRO-NINO, ELINA - University Of California, Davis; YOKOTA, SEIJI - US Department Of Agriculture (USDA); STACY, WILLIAM - University Of California, Davis; Seshadri, Arathi

Submitted to: Heliyon
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2022
Publication Date: 8/28/2022
Citation: Lastro-Nino, E., Yokota, S., Stacy, W.H., Seshadri, A.H. 2022. Dietary phytochemicals alter hypopharyngeal gland size in honey bee (Apis mellifera L.) workers. Heliyon. 8(9). Article e10452. https://doi.org/10.1016/j.heliyon.2022.e10452.
DOI: https://doi.org/10.1016/j.heliyon.2022.e10452

Interpretive Summary: Honey bees continue to face challenges resulting from habitat loss related compromises to nutrition, exposure to agrochemicals and devastating pests and pathogens. Honey bees depend on plants for their nutritional needs. Pollen and nectar produced by plants, in addition to protein, lipids and carbohydrates, provide bees with a wealth of micronutrients including phytochemicals such as flavanols and alkaloids. Continued habitat degradation and compromised access to quality nutrition, has negatively impacted gut microbial flora and overall health of bees. Earlier studies demonstrated that phytochemical supplementation to worker bees increased their longevity, pathogen tolerance and gut microbiome abundance. Here, we provide evidence that dietary supplementation with phytochemicals has an inconsistent effect on physiological traits such as the hypopharyngeal gland (HPG) size. Supplementation with p-coumaric acid or kaempferol increased HPG size in worker bees but supplementation with caffeine or gallic acid decreased HPG size as compared with control.

Technical Abstract: Honey bees, being efficient pollinators of several important fruit, nut and vegetable crops, contribute to the agricultural economy by providing essential pollination services. Honey bee health has been a concern for decades and a combination of factors including nutrition, agrochemicals, pests and diseases have all been identified as potential causes affecting bee colony performance and survival. Bees depend on plants for nutrition with pollen as the predominant protein and lipid source, and nectar, the source of carbohydrates. In addition to these macronutrients, pollen and nectar also contain important micronutrients, specifically phytochemicals that have been shown to improve longevity, pathogen tolerance and gut microbiome abundance in worker bees. Here we investigate the impact of four beneficial phytochemicals – caffeine, kaempferol, gallic acid and p-coumaric acid on hypopharyngeal gland (HPG) size of nurse bees. Newly emerged bees were provided with 25 ppm of phytochemical in 20% (w/v) sucrose solution and the size of HPGs were measured after a 10d period. Phytochemical supplementation had an inconsistent effect on HPG size with a significant increase seen when bees received ¬p-coumaric acid or kaempferol and a significant decrease in size seen in bees receiving caffeine or gallic acid. P-coumaric acid has been shown to have a role in worker bee ontogeny aligning with our finding of enhanced HPG development in nurse-aged bees. Caffeine promotes learning and memory which are important for forager-aged bees and a decrease in HPG gland size is also associated with bees transitioning from nurses to foragers. Access to phytochemicals is important for bees to perform different tasks that maintain healthy colonies. Our results reiterate the importance of access to phytochemicals in bee diet through natural habitats that provide a diversity of pollen and nectar sources or through dietary supplements that need to be standardized for bee colonies.