Queenless colonies contribute to the male breeding population at honey bee drone congregation areas

Honey bee workers can lay eggs that result in viable males (drones). In queenless colonies, workers activate their ovaries and lay eggs, both in their own colony and in other queenless colonies. While worker reproduction and reproductive parasitism are well demonstrated, the direct contribution of reproductive workers to the gene pool is unclear. Queenless workers mostly lay their eggs in worker-sized brood cells. The resulting drones are smaller than normal drones. We determined two measures of forewing size in drones reared in drone-sized cells (DC) and in worker-sized cells (WC). Forewing length and width were 5.78 ± 0.26 mm (± SD) and 1.27 ± 0.08 mm, respectively, for drones reared in DC, and 5.01 ± 0.21 mm and 1.11 ± 0.05 mm for drones reared in WC. Discriminant function analysis indicated that forewing length alone is sufficient to differentiate DC and WC drones. To determine the contribution of worker-laid drones to the mating population, we sampled males at a natural mating lek using a Williams’ drone trap every month for 12 months. We used the discriminant function to assign drones as being DC or WC based on their forewing length and a strict classification criterion of ≥ 0.99% posterior probability of assignment to one or other group. We estimate that about 0.23% of sampled males were reared in WC and were, therefore, likely to have been laid by workers. Our results suggest that queenless workers and queenless colonies make a small contribution to the male mating population, and that this contribution may be sufficient to provide ongoing selection for worker reproductive parasitism.