Egg laying: blame it on the context

Bumblebee queens have a lot to take into consideration when they are trying to start their nests in spring. The queens lay eggs which, once hatched, will create a colony of bumblebees all helping out in different ways to grow the colony throughout the summer season. But let's rewind: the colony only exists because of the queen. She has to figure out when and where to start laying her first eggs, which can be of vital importance to whether the colony will survive. At this time in her life, the queen is solitary, independent of other bumblebees around. But as soon as the first bumblebee worker emerges, she is no longer isolated and has become part of a colony, where bees can interact with other bumblebee workers. Blanca Peto, Claudineia Costa, Meghan Moore and Sarah Woodward, from University of California, Riverside, USA, looked at how these different social contexts – isolation versus being part of a colony – affect when and how queens lay eggs.The researchers decided to investigate Bombus impatiens bees, the only commercially available bumblebee species in North America. In their first experiment, they simply looked at when queens laid eggs after mating with a male bumblebee. They checked the cages that the queens resided in every day to see whether there were any eggs present. Once they saw the first eggs, they photographed the nests daily to see when the first worker emerged.Next, Peto and colleagues looked at how the presence of adult worker bees affected the queen's egg-laying rate and the number of eggs in each egg cup before the queen paused laying eggs, which probably allows the queen to coordinate egg laying with the emergence of new workers that take care of these eggs. Then, the researchers looked at the queens’ ovaries at six different stages of colony development and at how developing bee eggs, larvae and pupae, collectively known as brood, affected when the queens laid eggs. In addition, the researchers added additional brood (older larvae or late-stage brood) to the cages with the mated queens to see whether this would affect the timing of egg laying for bumblebee queens during the pause.After observing the queens and their colonies in each of these scenarios, Peto and colleagues discovered that the timing of when queens lay eggs is always changing, depending on whether the queen is isolated or worker bees and developing brood are present. When queens are surrounded by members of a colony, they lay eggs at a faster rate. Additionally, the researchers realised that the queens reabsorb nutrients from their ovaries when they pause laying eggs. The team suggests that this occurs because egg laying is an energetically draining task, so perhaps the queens are diverting this energy so that they can care for their developing larvae and pupae when they cease laying eggs briefly.It seems that the egg-laying life of a queen bumblebee is dependent on what else is happening in the colony. This study has revealed more detail about the impact of colony conditions on when queens lay eggs, which all contribute to making the colony more successful.