Evidence for a queen-produced egg-marking pheromone and its use in worker policing in the honey bee

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Abstract
SUMMARY Worker-laid and queen-laid male eggs were transferred into combs of empty drone cells in four honey bee (Apis mellifera ligustica) colonies. Worker-laid eggs treated with an ethanol extract of queen Dufour's gland were removed by workers (worker policing) at a significantly lower rate than either untreated or ethanol-treated worker-laid eggs, but this effect was less when a 1:10 dilution was used and it disappeared at a 1:100 dilution. Worker-laid eggs that had been touched to an area of a queen at the base of the sting and between the sting sheaths (‘sting- wipe’ treatment) were also removed at a significantly lower rate than untreated worker-laid control eggs. In all trials, the removal rate of worker-laid eggs exceeded that of queen-laid eggs. Queen-laid eggs treated with the polar solvents methanol and ethanol were removed more rapidly than those treated with the less-polar hexane and methylene chloride, but it was not possible to determine if this was because methanol and ethanol were more effective at removing a possible pheromone or because they caused more damage to the eggs. The results support a hypothesis that recognition of worker-laid eggs during worker policing is via a queen-produced egg-marking pheromone. Possible sources of pheromonal material besides the Dufour's gland are discussed.