Honey has been shown to have anti-microbial properties, but it turns out that this might not be the only fluid that bees produce with pathogen-killing abilities. It seems that the semen of honeybees contains antibodies that help defend the insects from a potentially deadly sexually transmitted disease, and that the males might be passing this protection on to the queens when they mate.
Discovered by a team of researchers from the University of Western Australia’s Centre for Integrative Bee Research, it appears that the honeybees’ semen can kill the fungal pathogen Nosema apis in two different ways. Proteins found in the seminal fluid can cause the fungal spores to germinate, disrupting the life cycle of the fungus, while another molecule simply killed the spores outright. The researchers hope that the knowledge that the immune system of bees is far more complex than previously thought could lead to the development of colonies of honeybees resistant to the pathogens currently causing their dramatic decline.
Honeybees are affected by all sorts of different pathogens, but the Nosema apis fungus is particularly interesting. Bees are normally infected when they come into contact with other bees that are carrying the spores of the fungus, but it was also discovered that the pathogen can be passed on sexually. Normally, queen bees only mate once with multiple male drones, and so this mode of transfer for the disease doesn’t happen very frequently. But to try and protect against this, it seems the semen has evolved anti-microbial properties.
The researchers discovered this special characteristic while trying to understand the declining fertility of Australian honeybees. The isolated continent is vitally important for the global health of the insects, as it is the only continent (except Antarctica) where the deadly Varroa mites have yet to reach. But this isolation also has its downside, as the bees that live in Australia are inbred. It is thought, but not yet fully understood, that this inbreeding could be leading to their observed decline in fertility.
It was while looking at the drones’ semen that the researchers noticed the novel properties in fighting the fungus. To get the semen of bees, the scientists first had to catch the drones as they were returning to the hive. They then placed them in little enclosures and sedated them with chloroform before manually squeezing their abdomens and then collecting the ejaculate with a pipette. According to the paper, published in the Proceedings of the Royal Society B, this technique leaves the bees unharmed.
The discovery of the semen’s anti-microbial properties goes to highlight just how complicated the honeybees' immune system is, and how much there is still to learn about it. The fact that these proteins are expressed in the seminal fluid could give researchers an easy way to look at how bees fight infection, which is a lot easier than studying it in the bodies of the insects, and could give an insight into how we could breed bees resistant to the deadly Varroa.