Bumblebees are a nifty bunch: When pollen is scarce and plants near the nest are not yet blooming, workers have developed a way to force them to bloom. Research published Thursday inScience, shows that insects pierce plant leaves, causing them to bloom, on average, 30 days earlier than they would otherwise. It is not yet clear how the technique evolved and why plants respond to bumblebee stings when flowering. But the researchers say the discovery of a new behavior in such a familiar creature is remarkable.
“This is one of those really rare studies that looks at a natural phenomenon that hadn't been documented before,” says John Mola, an ecologist at the US Geological Survey's Fort Collins Science Center in Colorado, who was not involved in the study. . The new finding "offers all kinds of potential questions and explanations" about how widespread the behavior is and why it occurs, he says.
Study co-author Consuelo De Moraes, a chemical ecologist at the Swiss Federal Institute of Technology in Zurich (ETH Zurich), says that she and her colleagues were observing a species of bumblebee in an unrelated laboratory experiment when they noticed insects damaging the plant leaves and wonder why. "Initially we wanted to see if they were removing the tissue or feeding on the plants or bringing leaf material to the nest," she says. And because previous research had shown that stress could induce plants to bloom, de Moraes and his colleagues also wondered if bees might be creating flowers on demand.
To find out, the team placed pollen-deprived bumblebees along with tomato and mustard plants in mesh cages. The bees soon cut several holes in the leaves of each plant using their jaws and proboscis. As proof, the researchers tried to replicate the bumblebee damage on additional plants with tweezers and a razor. Both sets of plants with injured leaves bloomed faster, but those pricked by bees bloomed weeks earlier than those clipped by the scientists, suggesting that chemicals in the insects' saliva may also be involved.
The researchers then moved out of the lab to see if the bumblebees would continue to harm non-flowering plants near their nest, even if flowering plants were available further afield. They did so. "If they have to search for food further afield to find flowers, it might make sense to do this harmful behavior near the nest if it helps to get local resources online sooner," says study co-author Mark Mescher, also a chemical ecologist at ETH Zurich.
The findings suggest that bees' behavior is an adaptation that maximizes pollen-seeking efficiency, but they don't definitively confirm that hypothesis, says Mescher Neal Williams, an entomologist at the University of California, Davis, who was not involved in the study, says that the possibility is compelling and warrants further investigation. "For something to really be defined and clearly understood as adaptive, we'd like to be able to say that the behavior was evolving because it contributed a relative fitness benefit to the colony," he says. In bees and other eusocial organisms, a single queen produces offspring and the workers are sterile, so natural selection operates throughout the nest.