The role of gland secretions from brood bees and of larval nutrion in caste determination in eusocial stingless bees and bumble bees

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A main goal of the project is the identification of compounds that mediate caste specific development in larvae of a primitvely eusocial bumble bee (Bombus terrestris) and a highly eusocial stingless bee (Schwarziana quadripunctata). We will investigate whether geraniol (or chemically similar compounds) from labial gland secretions of nurse bees acts as primer pheromone triggering queen development, as we recently found in another stingless bee (Melipona beecheii). The comparative approach to investigate caste determination including primitively eusocial bees, in which larvae are directly fed by nurse workers (Bombus), highly eusocial bees that produce regular and miniature queens in mass provisioned large or normal sized brood cells (Schwarziana) and highly eusocial bees that solely produce queens from normal sized brood cells (Melipona) will shed light on the evolution of caste determining mechanisms in eusocial bees. The second goal of the project is the identification of the proximate mechanism, by which geraniol mediates queen development in M. beecheii. We will test our hypothesis that the terpene geraniol serves as an essential precursor molecule for the synthesis of the terpenoid juvenile hormone, which is produced in high amounts in larvae developing into queens. Bioassays with deuterium-labelled geraniol fed to larvae will show whether they synthesize deuterium-labelled juvenile hormone. Finally, analyses of volatiles from plant derived larval food will reveal whether caste determining compounds are contained in pollen or nectar, the ancestral food for bee larvae. These investigations will allow providing conclusion for the evolutionary origins of caste determining compounds in eusocial bees.