European Drone Honeybees More at Risk of Worrisome Parasitic Infection

The intestinal parasite Nosema ceranae takes root in male European honeybees more readily than in females, according a research team from Bern, Switzerland.

Although the parasite, which causes an intestinal disease, originated in Asia and is predominant in Asiatic honeybee populations, it is spreading through Europe and the rest of the world. This parasite contributes to a high number of colony deaths across many regions in the Northern Hemisphere.

University of Bern researchers report that male honeybees' susceptibility to the disease highlights their delicate nature.

Honeybee colonies are divided into castes. Females, which are workers and queens, are diploids, meaning they carry two copies of each chromosome. Males, which are drones, are haploids, only carrying one chromosome set.

"The haploid susceptibility hypothesis predicts that haploid males are more prone to disease compared to their diploid female counterparts because dominant genes on one chromosome copy have the opportunity to mask mutated genes on the other copy in diploid organisms," the researchers said in a statement.

Writing in the journal PLOS One, the University of Bern researchers demonstrated that, compared to females, male honeybees are "significantly more susceptible" to infection by N. ceranae.

Because of the threat of colony collapse disorder, which is mysteriously killing bee colonies around the world, researchers and bee experts are scrambling to find solutions to that and other risks to bee colonies, such as parasitic infections.

Gina Tanner, a doctoral student involved in the investigation, said that it's worrisome that male honeybees die from N. ceranae infection more readily than females.

"Although drones do not perform important colony maintenance functions like cleaning and feeding like the workers, they are responsible for mating with queens so that the next generation of honey bees can be produced within a colony. Without strong, fit drones, the chance of successful matings with queens could be severely compromised," she said.

Thriving honeybee colonies are essential for a sustainable ecosystem. In addition to producing honey, the bees are major pollinators. In Europe alone, the value of the crops farmers rely on bees to pollinate is estimated at 4 billion euros ($5.4 billion) annually.