Abstract
Detailed social and phenological data collected from nesting aggregations exist for relatively few sweat bee species because nesting aggregations are rarely found in large numbers, even when local populations are highly abundant. This limits researchers’ abilities to assess the social status of many species, which in turn, limits our ability to trace the sequence of evolutionary steps between alternative social states. To address this problem, we demonstrate the utility of rehydrated, pinned specimens from pan trap and netting collections for generating inferences about the phenology and social status of a well-studied sweat bee species, Lasioglossum (Dialictus) laevissimum. A detailed comparison of phenology and reproductive traits, between pinned specimens and those in a previous nesting study, produced similar results for bivoltine foraging activity and eusocial colony organization typical in this species. We then used pinned specimens from monitoring studies to describe, for the first time, the foraging phenology and social behaviour of two additionalDialictusspecies,L. hitchensiandL. ellisiae. BothL. hitchensiandL. ellisiaeeach exhibited two peaks in abundance during their breeding seasons, indicating two periods of foraging activity, which correspond to provisioning of spring and summer broods. Differences in body size, wear, and ovarian development of spring and summer females indicated thatL. hitchensiis most likely eusocial, whileL. ellisiaeis either solitary or communal. This study demonstrates that analyses of specimens obtained from flower and pan trap collections can be used for assessing the phenology and social organization of temperate sweat bees in the absence of nesting data. The phenological and social lability of many sweat bee species make them ideal for studying geographic and temporal variability in sociality, and analyses of pan trap collections can make these studies possible when direct observations are impossible.
Highlights
In temperate zone sweat bees (Hymenoptera: Halictidae), flight phenology is closely linked to sociality
We used specimens collected via pan traps, netting from flowers, and sweep-netting to examine the social status of L. laevissimum, L. hitchensi and L. ellisiae
Lasioglossum hitchensi and L. ellisiae were selected because large numbers of specimens had been identified and collected, and because these two species are likely to be phylogenetically informative in future studies
Summary
In temperate zone sweat bees (Hymenoptera: Halictidae), flight phenology is closely linked to sociality. Others exhibit social and phenological polymorphism within populations, with solitary nest foundresses provisioning a single brood of reproductives, while eusocial foundresses produce a worker brood that subsequently provisions the second brood (Packer et al 1989; Packer 1990). The strength of the link between a bivoltine phenology and eusociality is well known phylogenetically, leading to the hypothesis that in halictine bees evolutionary transitions to eusociality involved two major steps: an initial transition from univoltinism to bivoltinism, and a subsequent step from solitary breeding to eusociality (Brady et al 2006)
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