Territorial behaviour in males of three North American species of bumblebees (Hymenoptera: Apidae, Bombus)

Abstract
The behaviour of males of the bumblebees Bombus nevadensis nevadensis, B. griseocollis, and B. rufocinctus was examined at sites in Colorado and Montana, U.S.A. Males of all three species defended individual mating territories on which they scent marked plants with cephalic chemicals, which we hypothesize to be sex pheromones. Males aggressively excluded conspecific males from the vicinity of scent-marked plants for several hours each day. At times on certain B. griseocollis territories, the great number of intruding males resulted in a near breakdown of the territorial system, with repeated aggressive interactions and turnover. In preliminary chemical analyses, dichloromethane extracts of heads of B. nevadensis and B. griseocollis were each dominated by single components, while those of B. rufocinctus, in each population studied, had three major components. Extracts of plant parts scent marked by males reveal the presence of the cephalic chemicals not present on unmarked control plants. Mating is initiated on or near territories. The behavioural and morphological correlates of male mating systems in the genus Bombus and other aculeate Hymenoptera are discussed.

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