Smell You Later Sweat Bee!

STRI intern Callum Kingwell holds a sweat bee stick nest he collected from Barro Colorado Island.

Smithsonian Tropical Research Institute (STRI) intern Callum Kingwell is currently working with sweat bees to discover how sweat bee queens communicate their dominance status through chemical odors called pheromones. His research focuses on queen pheromones called lactones that coat the nest as well as the queen herself to transmit information about the reproductive status of the queen. This information can be responsible for whether female offspring stay to help raise their future siblings, or leave the nest to start their own. Callum is conducting experiments to determine if the amount of lactone emitted by the queen is really the reason for her daughters to stay behind, and if it is really representational of her fertility status. He writes more about his research in STRI’s virtual magazine ‘Tropicos’:

“Queens of the sweat bee species Megalopta genalis build their nest in dried-out sticks in the forest understory. Some queens raise one or two subordinate daughters as workers who tend brood cells and feed their mother with nectar collected during brief foraging forays at dawn and dusk. Other queens raise only males and potential future queens that eventually move away, leaving their mother to attend to the nest and brood alone.

The simplicity of this system makes it possible for Callum Kingwell to discover organizational principles that may apply to much more complex social insect societies where survival depends on the coordinated actions of tens of thousands to millions of workers.

A STRI short-term fellow from Cornell University, Kingwell asks how sweat bee queens communicate their dominance status through chemical odors called pheromones.

‘As an audiovisual species we’re focused primarily on sights and sounds, yet for many organisms olfactory stimuli are much more prominent,’ he says. ‘A lot of behaviors are actually mediated by factors that are totally unseen.’

Gamblers and Cheaters

Lactones may also influence whether or not the queen’s daughters stay to help her raise their little sisters. If the queen is older or weaker, her daughters might gamble on their own luck and fly off to start their own nests. But by helping raise a fertile queen’s offspring, older sisters guarantee the survival of some of their own genes, which they share with their younger siblings.

‘So if there is a strong queen fertility signal, it’s in the workers best interest to serve the queen,’ says Kingwell.

Kingwell runs two main experiments as part of his project. In the lab, he records the physiological response of female antennae to the lactone 20-eicosanolide, which he suspects partly conveys a queen’s reproductive prowess and may induce daughters to stay at home.

The other, a field study on Barro Colorado Island, examines whether queens that emit strong chemical signals are, in fact, especially fertile. Queens who emit strong signals but do not produce many offspring may be cheating subordinates into helping when the supposed benefits do not exist. The risk in keeping a subordinate is that if the queen’s dominance signals diminish, her daughter may overthrow her and take over the nest.”

You can also find out more about STRI here.