Chemical ecology involved in invasion success of the cuckoo bumblebee <Emphasis Type="Italic">Psithyrus vestalis</Emphasis> and in survival of workers of its host <Emphasis Type="Italic">Bombus terrestris</Emphasis> |
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Authors: | A Sramkova M Ayasse |
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Institution: | (1) Department of Experimental Ecology, Institute of Zoology, Albert-Einstein-Allee 11, 89069 Ulm, Germany |
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Abstract: | In bumblebees all species of the subgenus Psithyrus are social parasites in the nests of their Bombus hosts. In the bumblebee B. terrestris we investigated how colony size influences survival rates of nest entering females of the social parasite Psithyrus vestalis. Furthermore, we studied whether the host worker’s dominance status and age are reflected in its individual scent and whether
Psithyrus females use volatiles to selectively kill host workers. The survival rate of Psithyrus vestalis females drops from 100%, when entering colonies with five workers, to 0% for colonies containing 50 host workers. Older host
workers, born before the nest invasion, were selectively killed when Psithyrus females entered the nest. In contrast, all workers born after the nest invasion survived. The host workers’ dominance status
and age are reflected by their individual odours: newly emerged workers produced a significantly lower total amount of secretions
than 4-day-old workers. In chemical analyses of female groups we identified saturated and unsaturated hydrocarbons, aldehydes,
and unsaturated wax-type esters of fatty acids. In a discriminant function analysis different worker groups were mainly separated
by their bouquets of hydrocarbons. Killed workers release significantly more scent and of a different chemical composition,
than survivors. Survivors alter scent production and increase it beyond the level of the killed workers within 1 day of the
invasion. The Psithyrus female clearly maintains reproductive dominance utilizing these differences in the odour bouquets as criteria for killing
workers that compete for reproduction. |
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Keywords: | Social parasitic bumblebees Bombus terrestris Psithyrus vestalis Chemical signature of host workers Survival rate of host workers and parasite females |
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