Male behaviour in two bumblebees, Bombus nevudensis auricomus and B. griseicollis (Hymenoptera: Apidae)

The mating system of the bumblebees Bombus nevadensis and B. griseicollis involves apparent territorial defence of perch sites near or within visually conspicuous trees. Non–contact chases between perch owners and intruders are rare in B. nevadensis and more common in B. griseicollis. The perches of B. nevadensis are in open areas whereas those of B. griseicoilis are within trees or in sites shaded by trees. The same locations may be occupied on 2 different years. Individual males may return to favoured perches over periods ranging from 2 to 24 days. Males of both species scent–mark spots near their perches early in the morning and then scan visually for passing females for as much as 7–8 h daily. The landmark–based mating system of these bumblebees is similar to that of some other insects and closely resembles the pure dominance (lek) mating system of certain vertebrates. Some hypotheses for the evolution of diversity in male mating tactics among bumblebee species are presented.