October 5, 2013
Of Bees And Bravery
The scientists in the study tested to see how individual bees and colonies react to multiple predators and multiple food sources at the same time.
Bees help flowering plants reproduce through pollination while they suck on nectar from the flowers. Predators such as hornets disrupt this give-and-take relationship by not only killing the bees, but also scaring them enough to keep away from the plant.
Two varieties of hornets attack the Asian honey bees when they hunt for nectar, one small-sized and the other gigantic – the bigger one understandably considered more dangerous by the bees. The hornets can be very sneaky, zeroing in on the flowers that the bees favor most and hunting them down.
But the bees have their own defense mechanism: they can huddle around the attacking hornet and kill it with their collective body heat (a phenomenon called “heat-balling”). Yet, when scared, they prefer to stay away from a good food source rather than defend themselves, according to the study jointly conducted by scientists at the University of California, San Diego and Yunnan Agricultural University in China.
The scientists exposed the honey bees to varying qualities of sugar solutions, with and without the presence of predators. They combined “high risk” with “high reward” – the bigger hornet in the feeder with the sweetest sugar solution, the smaller hornet in the middle and no hornets in the feeder with the least sweet solution (the “safe” feeder).
When there were no predators, the bees naturally flocked more to the feeder that had the best food source.
When the predators were introduced, however, colonies cut down the number of bees they sent to those specific feeders by half – even if the food quality there was better than the “safe” feeder. They also started spending less time at these “dangerous” feeders.
On the other hand, individual bees were more daring: 80 percent of them visited the “dangerous” feeders even when when the hornets were present. Although they mostly avoided the feeder with the bigger hornet, they didn’t reduce their visits to the intermediate one with the smaller hornet. The individual bees were willing to risk taking on the smaller hornet to get a better quality of food than the “safe” feeder, the researchers believe.
More individual bees also visited the “safe” feeder than the colonies which simply reduced their visits to all feeders when they felt threatened.
It’s not just the presence of another, bigger insect that puts the bees on the defensive, it is the threat that they pose, the researchers believe. When testing with a feeder that had butterflies, for instance – which do not attack the bees – the bees continued hunting for nectar undaunted.
Earlier studies have mostly focused on a single predator at a time, or on predators that “sit and wait” such as crab spiders. These results show how fear of multiple predators can affect how the bees feed and how long they stay on the flower, the researchers wrote.
Bees are highly social creatures and many flowering plants depend on the collective feeding habits of bees to reproduce and survive. However, fear can have a great effect on the colony’s decision to search for food. Studying how fear modifies the colonies’ behavior will help scientists understand its indirect effects on pollination, and on the ecosystem as a whole, the researchers believe.