Sick bees smell different

Honey bees infected with a gut parasite smell different, which could allow bee colonies to detect disease and influence behaviour inside the hive, finds new research.

A team from Cardiff University have uncovered new information about Vairimorpha infection in bees, showing that the parasite which causes gut infection changes volatile organic compounds (VOCs) emissions – causing infected bees to smell different to the healthy colony.

Dr Ayman Asiri, Cardiff University School of Biosciences, said: “Infection is known to change the VOCs emitted in a wide range of animals, but the effects in adult honey bees have remained unexplored.”

In the new study, researchers collected adult honey worker bees, separating them into an infected and an uninfected control group. The researchers then tracked infection over 14 days, sampling VOCs and analysing changes in VOCs emitted by the bees.

They found that the profiles of the types of VOCs emitted by infected and uninfected bees differed significantly, with differences at their strongest at 6 and 12 days post-infection. This suggests that infection odours are dependent on the stage of infection and may be linked to the level of infection at those given time points.

The researchers found that no VOCs were exclusive to infected bees. However, the amounts of chemical compounds changed during infection. Two compounds - tetradecane and dodecane - were associated with early infection, and 3,4-dimethylbenzaldehyde was linked with late infection.

The progression of the parasite infection aligned with VOC changes, with differences coinciding with periods of rapid parasite growth, suggesting odour changes reflect underlying infection progression.

The researchers believe that the early-stage compounds may act as cues that trigger the avoidance or removal of infected bees. This may mean that VOCs contribute to a bee colony’s social immunity by helping workers detect and respond to infection through chemical cues.

Dr Sarah Perkins, Cardiff University School of Biosciences, said: “Our findings provide the first evidence that Vairimorpha infection alters the VOC profile of adult honey bees.

“Our findings show that infection by Vairimorpha infection does not produce a single diagnostic smell, but instead reshapes the entire volatile profile of adult honey bees in a time-dependent way.

“These robust shifts in VOC profiles may be used by colonies to detect disease, and our results suggest infection could influence social behaviour inside the hive.”

The research, Wake Up and Smell the Infected Bees: Volatile Cues of Vairimorpha Infection in Honey Bees, was published in Ecology and Evolution.