Evidence for a queen-produced egg-marking pheromone and its use in worker policing in the honeybee
Francis L W Ratnieks;
Worker-laid and queen-laid male eggs were transferred into combs of empty drone cells in four honey bee (Apis mellitera 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 ('stingwipe' 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 lesspolar 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.