In Race to Save Honeybees, New Test to Identify Colonies That Can ‘Smell’ Disease Is Key

Honeybees are some of the most vital workers in the U.S. With a production value of nearly $350 million, they’re responsible for pollinating more than 90 crops and play a big role in our food supply and economy.

But America’s buzziest workers are in trouble, plagued by viral diseases and mite infestations. Although the picture doesn’t look good, a group of researchers says they may have identified a way to make bee colonies stronger. The key is in their sense of smell.

Honeybees can smell disease. It all starts with the eggs. In a honeybee colony, a queen lays eggs, which resemble small grains of rice, inside small hexagonal holes in the hive, with one egg going into each cell. After the egg hatches into a larva, nurse bees take over and feed it.

Once it’s big enough, the nurse bees place a cap of wax of it, protecting it during its next stage as pupa. The pupa stage is the stage where the baby bee develops eyes, legs, wings, and other body parts. When the bee is ready, it’ll chew through the wax capping and join the rest of the hive.

However, not all eggs turn into healthy bees. There are times when the developing bee is sick or dies in its cell, which is when the nurse bees get to work. These bees can detect when there are health problems with the pupa and will step in to uncap the cell and remove it for the protection of the rest of the hive. The process of detecting when bees are sick, which relies on pheromones, is known hygienic behavior.

Searching for disease-resistant bees. Not all bees perform hygienic behavior. These types of honeybees are highly coveted because it means they’re more resistant to disease. Colonies that don’t manage their disease cost beekeepers time and resources. Furthermore, pathogens that develop in managed colonies can spread to wild bee populations.

“It's definitely more desirable for a beekeeper to have bees that are better adapted at taking care of their diseases themselves rather than using chemical treatments and interventions to try to reduce these pathogen loads, which of course may have negative impacts on the bees,” Samantha Alger, the director of the Vermont Bee Lab at the University of Vermont, said in a statement. “Now the trick is how does a beekeeper identify a colony that is really hygienic?”

Alger and other researchers believe they’ve found a new tool that can help identify which colonies practice this type of behavior. It’s called UBeeO, a test that’s designed to test the abilities of nurse bees.

UBeeO. As mentioned earlier, nurse bees can sense when there’s a problem with brood in their cells. UBeeO uses synthetic pheromones that mimic the chemicals that diseased or dying brood give off.

Until now, beekeepers have performed hygiene tests that focus on bees’ ability to detect dead brood, according to the University of Vermont. One of these methods is called the freeze brood assay, which involves pouring liquid nitrogen over some capped cells and waiting a day to see if the nurse bees remove the dead.

“Rather than using liquid nitrogen to kill the developing pupae or larvae, you are using a blend of synthetic pheromones that mimics the same chemicals that are emitted by dying or diseased brood,” Alger said. “So rather than testing the bees’ ability to identify dead brood, you are testing the bees’ ability to identify diseased brood, which means that this test is a little bit more selective and realistic to what bees experience.”

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Results. To carry out the UBeeO test, researchers sprayed an area of capped sells with synthetic pheromones and waited two hours to see if the nurse bees responded by checking on the brood. The percentage of cells that are uncapped by the nurse bees represents the UBeeO score.

The researchers found that colonies with higher UBeeO scores, meaning that they were more likely to perform hygienic behavior, had lower levels of disease load. Specifically, they determined that UBeeO could identify colonies that were resistant to pests and diseases that can destroy bee populations, including Vairimorpha (also known as Nosema) and fungal infections like chalkbrood. The researchers published their results in a study in Frontiers in Bee Science.

Overall, researchers say that incorporating UBeeO selection into honeybee breeding programs could produce multiple benefits, including enhancing colony resistance to disease and reducing the need for chemical treatments.

“By leveraging tools like UBeeO to identify and breed colonies with enhanced disease resistance, beekeepers can improve the overall health and productivity of honey bee populations, contributing to the sustainability of apiculture and the productivity of pollinator-dependent crops worldwide,” they write.

Images | Shelby Cohron | Bianca Ackermann

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