The role of gland secretions from brood bees and of larval nutrion in caste determination in eusocial stingless bees and bumble bees
Final Report Abstract
Reproductive division of labor with cooperative brood care is one of the main characteristics of eusocial insects. It is based on the development of two physiologically and more or less morphologically distinct female castes, queens and workers. A key to caste development lies in the regulation of growth and development in the larval stages by colony intern factors, which can be a modification of the larval food or changes in the feeding behavior of the adult nurse workers. In social bees the exact mechanism of caste determination is completely unknown for almost all species. In the now finished project we investigated potential proximate mechanisms of caste determination in highly eusocial stingless bees (Apidae, Meliponini), as well as in a primitively eusocial bumble bees (Apidae, Bombini). The focus of analyses lay on the potential role of compounds secreted from labial glands of nurse workers and–in the case of Bombus terrestris–also queens because geraniol secreted from these glands in the stingless bee Melipona beecheii has been proven to induce queen development in larvae of this species when added to their provision. In particular, we looked for terpenoid compounds, like geraniol, in the nurse bees’ glands that may have a conection to juvenile hormone (JH) biosynthesis. One hypothesis for the mode of action of geraniol in M. beecheii states that the compound is an essential precursor molecule for a higher rate of JH biosynthesis, which, in turn, leads to a queen phenotype in adult bees. In the stingless bee Plebeia remota, a species that produces queens in large royal cells as well as in cells that do not differ in size from worker producing cells, we identified one candidate compound that was abundant in the labial glands of nurse workers and absent from the glands of foragers. This compound was a complex sesterterpene. Bioassays, in which synthetic samples of the setereterpene were fed to larvae of P. remota together with the provision within their brood cells, however, did not corroborate the hypothesis that its consumption by larvae induces queen development. It cannot be excluded without further analyses that the structure of the comlex sesterterpene has changed during transport from Germany to Brazil, thereby loosing its biological function. In the bumble bee Bombus terrestris we did not detect compounds in the glands of nurse workers that may be linked to queen development of female larvae during the final phase of the colony development, i.e., the competition phase. Rather, we found a series of fatty acid esters that are abundant in labial glands of queens collected during the social phase but almost absent from glands of competition phase queens. This led to the hypothesis that in bumble bees a queen produced primer pheromone may inhibit queen development in female larvae during the social phase, rather than that worker produced pheromones induce queen development during the competition phase. Bioassays testing this hypothesis were still running.
Publications
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(2014) Caste determination in eusocial bees: a key role of terpenoids? Proc. XVII. International Congress of the International Union for the Study of Social Insects (IUSSI), Cairns, Australia, p. 59
Jarau S
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(2014) Chemical ecology of bumble bees. Annu. Rev. Entomol. 59: 299-319
Ayasse M, Jarau S
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(2014) Kastendetermination bei Larven eusozialer stachelloser Bienen und Hummeln: Eine Schlüsselrolle von Terpenoiden? 61. Tagung der Arbeitsgemeinschaft der Institute für Bienenforschung, Marburg, Germany, p. 30
Jarau S
