Selection for non-diapause in the bumblebee Bombus terrestris, with notes on the effect of inbreeding

Bumblebees are generally believed to be annual insects. However, here we wi ll show that under laboratory conditions the bumblebee Bombus terrestris (L .) can produce a second generation without a period of cold storage (diapau se) or CO2 narcosis (a method to break diapause). It is also shown that thi s so-called non-diapause trait can be selected for. The percentage of non-d iapausing queens increased from 8% (minimum) to 97% (maximum) in two genera tions of selection. However, it was not possible to maintain isofemale non- diapause lines. Colonies of the fourth and fifth generation remained small (expressed in worker number) and produced a small number of queens. Also th e percentage of queens that started laying eggs (defined as the percentage non-diapause) decreased in the fourth and fifth generations. To study wheth er this decline of the non-diapause lines was caused by inbreeding, a contr ol experiment was conducted. In this control experiment queens were mated w ith their brothers (full-sib mating) for several generations and the number of queens that start egg laying was measured. This revealed that inbreedin g can have a negative effect on the egg-laying capacities of queens thus ca using the decline of inbred (non-diapause) lines.