Augochlora Sweat Bee

Photographed after capture [5]

When thinking of iridescence, it’s common to look to tropical leaf beetles, morpho butterflies, and the orchid bees. Smaller insects such as this ~1cm long sweat bee, though equally spectacular in their mercurial reflectance, are often left unnoticed. Next time you swat away a tiny figure hot in pursuit of your moisture and salt, take a closer look to see if it is one of these little jewels. This species (Augochlora cf. pura) belongs to the sweat bee family (Halictidae), a diverse clade of small bees comprising of over 2,000 species. Many sweat bees vary in iridescence, ranging from copper to green to blue in sheen, and there is also high intraspecific variation in color. Another common suit is a dark head/thorax contrasted with yellow and black stripes on the abdomen. To the untrained eye many halictid genera may appear to be incredibly similar morphologically, making identification difficult.

Highly eusocial bees are well known to regulate reproductive behavior through morphologically-differentiated castes and use of chemical cues. In contrast, many primitively eusocial species instead achieve colony functioning through direct physical interactions. These associations between dominant and subordinate individuals dictate the outcome of social competition within a colony, such as inhibiting ovary development to establish reproductive dominance. Colony dynamics of primitively social halictids has mostly focused on the genera Halictus and Lasioglossum. On the other hand, Augochlora was previously considered a solitary bee, as evidenced by the lack of social behavior in most Augochlorines— likely a reversal from an ancestral eusocial condition. However, in a 2015 study, social interactions were documented within captive colonies of A. phoemonoe, including antennation, ‘passing’, and tandem-running. Physical interactions between bees were found to significantly influence colony behavior— antennation resulted in higher pollen-collection activity by females, ‘passing’ elicited nest construction/maintenance, and tandem-running induced defensive behaviors such as nest guarding.

Nest structure of Augochlora amphitrite (Dalmazzo & Roig–Alsina, 2012)

In the tribe Augochlorini, nest construction is most often performed by a single mated female who tunnels into the soil. Augochlora exhibits similar behaviors, but remains the atypical of the bunch, obligately nesting in decomposing wood. Nests are characterized by a long narrow tunnel terminating in short offshoots which will house developing larvae. Particles of regurgitated decaying wood are compacted here to form adjacent cell chambers, additionally supported by pillars and surrounding natural cavities. Bees will only construct cells at night, but oviposition occurs during the day along with a pollen mass for larval nourishment. Nest architecture varies dramatically across the Augochlora genus, and even within a single species, tunneling and placement of cells is largely determined by which areas of wood have the most sound structural support. Augochlora has been given attention for its plasticity and variability in nest-building behavior (e.g. excluding phases of cell construction). If omission of cell construction behaviors increases, this may allow for the transition into a parasitic lifestyle. Alternatively, nestmates may cooperate through omitting behaviors performed by nestmates, so perhaps plasticity in nest-building may predispose them to evolving a higher degree of eusociality.

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