BACKGROUND: Cooperation and conflict in social insects are closely linked to the genetic structure of the colony.
Kin selection theory predicts conflict over the production of males between the workers and the queen and
between the workers themselves, depending on intra-colonial relatedness but also on other factors like colony
efficiency, sex ratios, cost of worker reproduction and worker dominance behaviour. In most bumblebee (Bombus)
species the queen wins this conflict and often dominates male production. However, most studies in bumblebees
have been conducted with only a few selected, mostly single mated species from temperate climate regions. Here
we study the genetic colony composition of the facultative polyandrous neotropical bumblebee Bombus wilmattae,
to assess the outcome of the queen-worker conflict over male production and to detect potential worker policing.
RESULTS: A total of 120 males from five colonies were genotyped with up to nine microsatellite markers to infer
their parentage. Four of the five colonies were queen right at point of time of male sampling, while one had an
uncertain queen status. The workers clearly dominated production of males with an average of 84.9% +/- 14.3% of
males being worker sons. In the two doubly mated colonies 62.5% and 96.7% of the male offspring originated
from workers and both patrilines participated in male production. Inferring the mother genotypes from the male
offspring, between four to eight workers participated in the production of males.
CONCLUSIONS: In this study we show that the workers clearly win the queen-worker conflict over male production
in B. wilmattae, which sets them apart from the temperate bumblebee species studied so far. Workers clearly
dominated male production in the singly as well the doubly mated colonies, with up to eight workers producing
male offspring in a single colony. Moreover no monopolization of reproduction by single workers occurred.