Differential distribution of resources for females on a dioecious plant affects the small–scale distribution of male of an oligolectic bee

C Polidori,M Federici

doi:10.32800/abc.2019.42.0267

Abstract

Females of the solitary digger bee Andrena florea Fabricius, 1793 (Hymenoptera, Andrenidae) nest in aggregations and collect pollen almost exclusively on dioecious plants of the genus Bryonia, making this species a good model to study the relationship between nest density, male density, male behaviour and female lecty. At a study site in the valley of the river Serio, in Italy, an aggregation of this bee showed low density of randomly distributed nests and was closely surrounded by B. dioica plants. Female nectar foraging and male feeding and mate–searching activity, confined to the host plants, peaked at similar hours across the day, while female pollen foraging peaked earlier. Males fed on plants of both sexes but seemed to perch waiting for females more frequently on male B. dioica leaves. Individual males more often visited only one of the male plants, for up to four days; here they did not interact aggressively with conspecifics, suggesting scramble competition in resource–based home ranges and not territoriality. These findings are preliminarily in accordance with the predicted resource–based rendez–vous sites at low nest density for oligolectic bees and the predicted occurrence of scramble competition in case of high male density. Additionally, males would maximize their mating opportunity by mainly perching on male plants, the only source of the most limited resource for females (pollen).

Highlights

Behaviour of male bees (Apoidea) has been studied in many species, showing that they use a wide range of behavioural strategies to find mates
In reference to the second, male scramble competition would be favoured if male density is high, while male territoriality would be favoured if male density is low (Paxton, 2005), with males in the former showing no fixed home ranges and males in the latter case showing defined territories that are actively defended from conspecific competitors
The different combinations of these traits lead to different outcomes in male behaviour: 1) when nest density is high and male density is low, male territoriality is expected at the nesting site; 2) when nest density is low and male density is high, male scramble competition at resource–based sites or at other sites is more likely; and 3) when nest density is low and male density is low we can expect male territoriality at resource–based sites or in other sites

Summary

Introduction

Behaviour of male bees (Apoidea) has been studied in many species, showing that they use a wide range of behavioural strategies to find mates (reviewed in Alcock et al, 1978; Eickwort and Ginsberg, 1980; Ayasse et al, 2001; Paxton, 2005) Such strategies are mainly driven by the fact that females select males to maximise their individual reproductive success, and by the fact that receptive females, which are generally prone to mate only for a short time after emergence, are a major limiting resource (Alcock et al, 1978). The different combinations of these traits lead to different outcomes in male behaviour: 1) when nest density is high and male density is low, male territoriality is expected at the nesting site; 2) when nest density is low and male density is high, male scramble competition at resource–based sites (in case of oligolectic species) or at other sites is more likely; and 3) when nest density is low and male density is low we can expect male territoriality at resource–based sites (in case of oligolectic species) or in other sites (in case of polylectic species) (fig. 1)

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Conclusion