Sick bees choose healthier food sources

Sick bees tend to consume higher-quality pollen compared to healthy bees, according to new research.

In a study published in Microbial Ecology, researchers were curious about how parasites impact the foraging behavior of honeybees and wild bees.

“Scientists and the public have long been interested in reports of bees dying — both managed honeybees and native wild bees — and implications for pollination and food security,” said Lori Lach, senior lecturer at James Cook University and senior author of the study.

Lach and her colleagues decided to use artificial flowers to determine the difference in foraging behavior between sick bees infected with parasites and healthy bees. They used European or western honeybees (Apis mellifera) in the study, some of which were infected with the gut parasite Nosema ceranae.

The team constructed the flowers so that they were identical to one another —except for the resources they contained. The three types of flowers they used contained either a sugar solution, high-quality pollen or low-quality pollen. Leaving the flowers in an apiary, they allowed the bees to choose which flowers they preferred to feed on. When a bee landed on the flower and began consuming its resources, the researchers recorded the type of flower and then captured the bee to determine its disease status.

The artificial flowers allowed the team to control the amount and nature of the resources present and to standardize the appearance of the flowers, Lach said. “This way we knew that the bee was making the choice of which flower to forage on based on the resource and nothing else.”

Lach and her colleagues determined that sick bees were more likely to choose the higher-quality pollen. Healthier bees showed no preference. Both healthy and sick bees foraged for pollen equally.

“We attributed this to the bees being influenced by the needs of the hive,” Lach said. The finding was consistent with their hive observations, in which they saw no relationship between the infection intensity in the hive and the proportion of bees foraging for pollen.

The higher-quality pollen also did not eliminate the parasite, researchers found, but it did increase the bees’ disease tolerance.

With increasing evidence that some pollinators are declining, Lach said, it’s important to understand more about factors that affect their behaviors.

“Pollinator foraging choices are what determines what is pollinated,” she said. “Flowers all vary naturally in nutritional qualities, and if pollinators continue to decline, flowers will increasingly be competing for pollinators. We need to learn as much as possible about factors that affect pollination.”