Nesting strategies of primitively eusocial bees: A model of nest usurpation during the solitary state of the nesting cycle

Abstract

In primitively eusocial bee species, Lasioglossum ( Evylaeus ) malachurum and L. ( E. ) pauxillum , solitary, overwintered gynes emerge in early spring and find nests. In the nests they provision several brood cells from which the first worker generation emerges several weeks later. During the initial nesting phase the gynes of both species are solitary. Shortly after the first foraging flights in L. malachurum , several gynes can be observed flying about the nest aggregation entering the temporarily empty nests of foraging nest owners. Occasionally, the gyne (the potential usurper) will remain in the nest at the entrance until the nest owner returns. At that time, either the usurper departs immediately, or a fight between the usurper and nest owner ensues. Fights can result in the death or serious injury of one of the combatants. The nest owner wins in most cases, but the usurper does stand a chance of taking over the nest. In contrast, in L. pauxillum nest takeovers are less common, and no such vicious fighting can be observed. We develop a dynamic simulation model to study the ecological and social conditions that promote nest usurpation of gynes of primitively social bees during the initial, solitary phase of the nesting cycle. The theory of evolutionary stable strategies is used to model the behavioral patterns of the gynes. Nest usurpation is an evolutionary stable strategy under fairly general conditions, but several factors, such as the probability of nest destruction, foraging mortality, the quality of the soil, and owner-intruder asymmetry, affect the time of the emergence of nest usurpation. The results related to the evolutionary stability of nest usurpation are illustrated by simulation examples.