Carlos H. Vergara, Departamento de Ciencias Químico-Biológicas, Universidad de las Américas-Puebla, Cholula, Puebla, Mexico
During colony foundation in bumblebees the queen is the only reproductive female. She suppresses ovarian development and ovipositon by workers by behavioral and pheromonal means. The “competition phase” of a colony is characterised by antagonistic interactions among workers and between workers and the queen. .
Psithyrus, (cuckoo bumblebees) are obligate social parasites in the nests of Bombus species. These parasites lack pollen collecting structures and rely on the host workers for the rearing of their offspring. Some New World Psithyrus species invade young colonies with few workers, coexist with the foundress queen and seem unable to control ovarian development of workers. Others invade larger colonies, evict or kill the queen, and may be able to supress worker ovarian development. Two European cuckoo bumblebees (P. vestalis, which is the speciific parasite of Bombus terrestris and P. bohemicus, which is the specific parasite of B. lucorum) were able to inhibit worker ovarian development and to reproduce in B. terrestris colonies. The effect of P. vestalis females on ovarian development of workers was statistically not different from the effect of B. terrestris queens (positive control) and significantly different from ovarian development inhibition measured in groups of workers alone (negative control). Ovarian development inhibition by P. bohemicus was not statistically different both from the positive and the negative control, indicating that this non-specific parasite is able to affect the ovarian development of workers, but not to the same extent as the queens of the same species or the females of the specific parasite. Females of Psithyrus species which are able to effectively suppress the development of ovaries in the workers of their host colonies will kill the queen upon invasion, since their reproductive success does not depend on the presence of the host queen to suppress egg laying and oophagy by workers.
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