Photo: Malcolm Rickets
Laying workers are usually unwelcome pests, but they are also a window into how insect societies may have evolved.
I didn’t understand why my queen cell builder wasn’t rearing any of my grafts. I usually have a deft grafting hand and expected the bees to start drawing out around 90% of yesterday’s queen cups into elegant fingers when I checked on them, but instead they were all cleaned out. Every single one of them. Spick and span.
I started to check the other frames in the builder. Could there be a rogue queen that I accidentally shook in? Or not enough food in the colony? Peering into the comb, I saw something unusual – about 7 or 8 eggs all piled on top of each other in a single cell. If that wasn’t enough of a clue, a few cells over, my eyes locked on to a worker casually shoving her backside into a cell, popping an undignified squat in broad daylight. That worker was laying eggs.
Laying workers are a nuisance to get rid of. It’s usually impossible to spot them, unless you’re lucky enough to catch them in the act of laying. If they’re around, the colony can dwindle into dysfunction. In that sense, they are a lot like social parasites – taking advantage of the colony’s resources to further their own reproduction, while the colony itself fails. Colonies with unusually high occurrences of laying workers have been reported in the US, the UK, New Zealand, Australia, and China. Most people despise these social parasites. But others want to understand them.
Last August, I had the pleasure of joining about a thousand other social insect scientists at the International Union for the Study of Social Insects (IUSSI) quadrennial conference held in Guarujá, Brazil. Ben Oldroyd, a professor at the University of Sydney, Australia, was the opening plenary speaker. He has devoted his career to understanding the mechanisms behind social cohesion in honey bees, that is, how and why honey bee workers evolved to be altruistic, or perform behaviors that benefit another individual at one’s own expense. Unlike laying workers, which are very rare in most honey bee colonies, normal, sterile workers selflessly give up their own ability to reproduce in favour of caring for their queen and nestmates.
But this sacrifice of reproductive potential isn’t actually “selfless” at all. Charles Darwin pondered the topic of worker sterility in the social insects as early as the mid-1800s, but an explanation for the evolution of worker sterility wasn’t provided until the 1960s by William Hamilton. Hamilton argued that a decrease in an individual’s fitness can still be evolutionarily favourable provided that it increases the fitness of kin. To illustrate the point, John Haldane, who worked out some of the early mathematics behind this claim, joked that he “would willingly die for two brothers or eight cousins.” In other words, the individual’s direct fitness decreases, but the indirect fitness (the ability of genetic relatives to survive and reproduce) increases, making the trade-off evolutionarily favourable. Soon, this concept of “inclusive fitness” became known as “kin selection.” In this light, a sterile worker honey bee’s dedicated care of her siblings, who either go on to reproduce (queens and drones) or continue the cycle of sibling care (workers) is not a selfless sacrifice, but a worthwhile investment.
Continue reading in the October 2018 issue of American Bee Journal.