INFLUENCE OF AGE AND POPULATION SIZE ON OVARIAN DEVELOPMENT, AND OF TROPHALLAXIS ON OVARIAN DEVELOPMENT AND VITELLOGENIN TITRES OF QUEENLESS WORKER HONEY BEE (HYMENOPTERA: APIDAE)

Abstract

AbstractWe examined the factors that might influence ovary development in worker honey bees, Apis mellifera L. Queenless workers at different ages (≤ 12 h, and 4, 8, and 21 d) were tested in cages for ovarian development. Newly emerged, 4- and 8-d-old, and 21-d-old workers had medium-, large-, and small-sized ovaries, respectively, suggesting that of the worker ages tested only 4- and 8-d-old workers are likely to become egg layers in a queenless colony. Also, we compared ovarian development of newly emerged workers that were caged for 14 d and allowed to consume either pollen or royal jelly to that of another group of workers similarly caged but screened so that they could only obtain food via trophallaxis from young bees. Ovaries of newly emerged workers that received food from young bees were as well developed as those of newly emerged workers allowed to take pollen or royal jelly directly. Screened workers also had lower but still elevated vitellogenin levels compared with bees having direct access to food. These results indicate that nurse-age bees functioning as pollen-digesting units affect the ovarian development of other workers and to a lesser extent vitellogenesis via food exchange. We compared the influence of group sizes of 25, 125, and 600 bees per cage on ovarian development for 14 d. The two groups of 25 and 125 bees had similar mean ovary scores, and higher scores than a group of 600 bees. Our findings suggest that nurse-age bees could play an important role in mediating worker fertility via trophallaxis, possibly by differentiating worker dominance status, and generally only young workers become fertile when a queen is lost in a colony. Vitellogenin is a more sensitive parameter to measure bee fertility, and might be a useful tool to further explore ovary development and egg laying in worker social insects. We recommend measuring haemolymph vitellogenin titres and (or) oocyte length of workers in a group of 25 bees per cage, supplied with 50% royal jelly in honey as a standard method to assess honey bee worker fertility in future experiments.