Ultrastructural and chemical characterization of egg surface of honeybee worker and queen-laid eggs

Worker policing in honeybees predicts the evolution of a mechanism to discriminate between queen- and worker-born eggs. Although it has been postulated that this discrimination is based on an egg recognition pheromone, neither the chemistry nor the glandular source were elucidated. To verify whether egg discrimination might be based on structural differences, we compared the ultrastructure surface of queen-laid diploid and haploid eggs to that of worker-laid eggs using SEM. Only small differences between the different types of eggs were found. Thus, at least based on the fine structure of the egg surface, queen eggs are indistinguishable from worker-laid eggs. To explore the chemosensory hypothesis for egg discrimination, we conducted a detailed comparative chemical analysis of the different egg types. The coating of all egg types was dominated by linear alkanes, but queen eggs, diploid and haploid, differed from those of workers on two accounts: 1. The diversity of compounds found on queen-laid eggs was much greater than found on worker-laid eggs, mainly due to the number of hydrocarbons. 2. Acetates of some fatty alcohols, alkenes and especially monornethylalkanes were characteristic to queen eggs. The origin of the two latter substances and the acetates is still unknown. Whether these compounds constitute the signal that enables police workers to discriminate between queen- and worker-born eggs remains to be investigated.