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International audience; To investigate whether flower selection in polylectic solitary bees is modulated by chemical imprinting to nest provisions, larvae of Osmia bicornis (L.) were reared on either Brassica napus L. (Brassicaceae) or Onobrychis viciifolia Scop. (Fabaceae). Flower preferences by adults were evaluated in multiple-choice behavioral tests based on visit number and duration, and flowers selected in the first three visits; data were compared to control bees from the wild. Females reared on B. napus showed only subtle increases in selection for this species, which was highly attractive to both control and experimental bees, masking any effects of imprinting; however, in the first three visits, experimental bees tended to select B. napus more frequently and consistently than controls. Bees reared on O. viciifolia were few and mostly males, which tended to visit this species more than controls. Rearing larvae on either plant affected bee attraction to other plant species. Overall, the data do not provide clear evidence of imprinting, but suggest that rearing bees on a single plant can both directly and indirectly affect flower selection by adults.

International audience; Stingless bees produce considerable numbers of virgin queens over the year, most of which are superfluous and get executed by the workers. Nothing is known yet about the sign stimulus that releases the worker attacks. In the present study we investigated the queen execution process in Melipona beecheii and found in both behavioral observations and experiments with caged living virgin queens that workers are not attracted to them from a distance by means of volatile chemicals. Furthermore, worker aggression, which is obvious towards virgin queens that run through the nest excitedly with their abdomen enlarged and the wings beating, was lowered to almost zero when we made the queens "behavior-less" by experimentally killing them. Our results clearly show that the sign stimulus for releasing the execution behavior in Melipona beecheii workers is not a chemical stimulus but the virgin queens' conspicuous behavior, which, we hypothesize, could act as a direct measure of their fitness.

International audience

Stingless bees (Apidae, Meliponini), which areclose relatives to honey bees (Apidae, Apini) andshare with them a highly eusocial colonial organi-zation (Michener, 2000), are remarkable for theirhabit of producing virgin queens throughout theyear (Engels and Imperatriz-Fonseca, 1990). Mostof these queens are not needed for a colony’s sur-vival or division, however, and get executed sometime after their emergence (Imperatriz-Fonseca andZucchi, 1995). Only little is known about the mech-anism that releases the execution behavior in work-ers or about how a particular virgin queen is cho-sen as a new queen. Recently, we found that in