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)

We examined the factors that might influence ovary development in worker ho ney bees, Apis mellifera L. Queenless workers at different ages (less than or equal to 12 h, and 4, 8, and 21 d) were tested in cages for ovarian deve lopment. Newly emerged, 4- and 8-d-old, and 21-d-old workers had medium-, l arge-, 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 r oyal jelly to that of another group of workers similarly caged but screened so that they could only obtain food via trophallaxis from young bees. Ovar ies of newly emerged workers that received food from young bees were as wel l developed as those of newly emerged workers allowed to take pollen or roy al jelly directly. Screened workers also had lower but still elevated vitel logenin levels compared with bees having direct access to food. These resul ts indicate that nurse-age bees functioning as pollen-digesting units affec t the ovarian development of other workers and to a lesser extent vitelloge nesis via food exchange. We compared the influence of group sizes of 25, 12 5, 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 gr oup of 600 bees. Our findings suggest that nurse-age bees could play an imp ortant role in mediating worker fertility via trophallaxis, possibly by dif ferentiating worker dominance status, and generally only young workers beco me fertile when a queen is lost in a colony. Vitellogenin is a more sensiti ve parameter to measure bee fertility, and might be a useful tool to furthe r explore ovary development and egg laying in worker social insects. We rec ommend measuring haemolymph vitellogenin titres and (or) oocyte length of w orkers in a group of 25 bees per cage, supplied with 50% royal jelly in hon ey as a standard method to assess honey bee worker fertility in future expe riments.