The laying of male eggs by bumble bee queens: an experimental reappraisal and a new hypothesis

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Abstract
The hypothesis that proximal factors associated with high worker density in a bumble bee (Bombus terricola) colony trigger laying of male eggs by the queen was examined in a series of four experiments. Neither the age of workers, the presence or absence of laying workers, nor the amount of pollen available to the colony affected the date of first male egg laying. Moreover, queens that had begun laying male eggs did not revert to laying female eggs after being removed from their colonies and placed in isolation. Instead, onset of male egg production appeared to be associated with the date of attainment of a critical worker/larva ratio in the colony. Functional considerations lead to the new hypothesis that queens monitor their egg-laying performance and begin to lay male eggs when it can be predicted that their female eggs will be raised as young queens.