Queen Bees Send Signals of Sexual History to Worker Bees
Queen bees communicate their reproductive status and sexual history to worker bees, according to a new study, which suggests the find may explain why honeybee populations are declining.
Writing in the journal PLOS One, researchers from an international team that includes entomologists from the Center for Pollinator Research at Penn State University, report that queen bees relay complex, nuanced information through chemical signals called pheromones. Prior to this research, it was generally believed that the queen bee only communicated simple information with pheromones.
"This study demonstrates that queen honey bees are conveying a lot of nuanced information through their pheromones," said Penn State's Christina Grozinger, a professor of entomology. "In addition, until now, no one knew if queen bees were manipulating workers into serving them or if they were providing valuable, honest information to workers. We have found that the information queens are conveying constitutes an honest message about their reproductive status and quality. The queens are 'telling' the workers that they are queens, whether or not they are mated and how well mated they are. In other words, whether or not they have mated with a lot of males."
Information about the queen bee's sexual history can be useful to mates, said Elina Niño, a post-doctoral researcher at Penn State. Previous studies have shown that colonies formed by queens with a promiscuous sexual history are more genetically diverse and therefore more likely to survive.
"Beekeepers have been very worried about their queens, since they seem to not be lasting as long -- a few weeks or months instead of one or two years," said Niño. "We know that workers will replace their queens when they are not performing well. So if worker bees are able to detect poorly mated queens and take steps to remove them, that could be an explanation for the rapid rates of queen loss and turnover that beekeepers have been reporting."
In the experiment for the latest study, the researchers took several queen bees and inseminated them with various quantities of semen, or saline solution as a control. Five queen bees were inseminated, one with a low volume of semen, one with a high volume; two other queens were inseminated with high and low volumes of saline solution, and a fifth queen was inseminated with nothing.
Later, the researchers dissected the queens and removed the gland that produces the queen bee pheromones. They presented extracts from the five different glands to worker bees and observed the extent to which they were attracted to the different samples.
The worker bees showed a preference toward the glands that were inseminated with semen versus saline solution, and they also showed preference toward the glad that was inseminated with the most semen.
"These results suggest that queens are signaling detailed and honest information about their mating state and reproductive quality to workers, and workers are capable of adjusting their behavior accordingly," Niño said. "When workers replace failing queens, it is particularly damaging to beekeepers since it can take up to three weeks for the new queen to begin laying eggs and another three weeks for the new workers to emerge as adults. This reduces the workforce and therefore reduces honey production and even pollination efficiency."
Niño said the research is important because the more we know about what affects the queen bee's health, the more likely it will be that high-quality queens can be bred, ensuring disease-resistant stocks of honey.