Lack of partner preference system for incest avoidance in the bumble bee Bombus terrestris

Inbreeding is caused by the mating of closely related individuals and produces a decrease in the offspring fitness and deleterious consequences for adults. In haplodiploid social Hymenoptera inbreeding has a further negative effect because of their particular mechanism of sex determination (sl-CSD), that causes the emergence, in half of the founded colonies, of unviable or sterile diploid males. When these males are able to develop until adult stage, as in bumble bees, they represent a huge cost for the colony. With respect to these high inbreeding consequences, a selection for mechanisms of inbreeding avoidance would be expected in bumble bees. Social recognition is one of the most common and efficient system to avoid inbred mating in social insect, but it is poorly studied in bumble bees. In this study we investigated the mating choice between siblings or non-siblings in queens and males of Bombus terrestris reared in laboratory. To investigate the role of mating behaviour in mating choice, the tests were performed both in cage and in tunnel. As opposed to what would be expected, we found that B. terrestris males and gynes do not show a mating preference for non-siblings compared to siblings (49.3% in non-siblings and 50.7% in siblings) and the mating latency was even shorter for sibling matings than for non-siblings ones.