If there were an international smelling bee, a deadly mite would be a favorite to win.
New research has revealed that Varroa mites, the most-serious threat to honeybees worldwide, are infiltrating hives by smelling like bees.
The Michigan State University-led study, appearing in the current issue of Biology Letters, shows that being able to smell like their hostess reduces the chance that the parasite is found and killed.
The parasites were originally found on Asian honeybees. The invasive species, however, revealed their versatility when they began infesting and killing European honeybees.
“The mites from Asian honeybees, or the original host, are more efficient in mimicking both Asian and European honeybees,” said Zachary Huang, MSU entomologist and one of the papers’ lead authors. “This remarkable adaptability may explain their relatively recent host shift from Asian to European honeybees.”
Chemical camouflage isn’t a new weapon in insects’ arsenals. Bolas spiders, for example, emit not one but three chemicals to emulate a sex pheromone to attract moths to eat. However, fooling socially sophisticated insects, such as honeybees, requires the faux scents to be spot-on.
That’s because the complex society of bees comprises tens of thousands of individuals divided by a sophisticated caste system. So, the mites aren’t simply tricking a solitary bee collecting pollen from a flower; they’re fooling an entire society. The stealthy mites do this by not only by being able to smell like bees, but also by effectively emitting the specific scents of small, individual colonies.
“They are essentially getting through the door and reaching the inner sanctum by using bees’ own complex communication codes against them,” Huang said.
The codes in which they communicate are hydrocarbons, the simplest of organic compounds. By tweaking the proportions of these chemical colognes, the mites give off the correct scents to fool their enemies.
Specifically, it’s the cuticular hydrocarbons, compounds released from hair-shaft glands, that emit scents that differentiate queens from fertile and infertile workers; it’s the smell that invokes acceptance or triggers aggression.
Huang and his team showed that mites are able to change their surface chemicals to an entirely different species of honeybees. Further, they also revealed that the mites were able to make these changes rather quickly – adapting in days rather than evolving over generations.
“Our study challenged the mites’ ability to modify their hydrocarbons,” Huang said. “Conversely, bees are adapting to detect these invaders. Our results give a clear illustration of an arms race between the parasites and the host bees based on chemical mimicry and its detection.”
Additional researchers contributing to this study include scientists from the French National Institute for Agriculture Research, Honeybee Research Institute (China) and the Research Institute for the Biology of Insect (University of Tours, France).
Huang’s research is supported in part by MSU AgBioResearch.
Zach gives a bit of background on the how the project unfolded…
The story goes back to 2004, when I invited a friend and colleague, Dr. Yves LeConte, from France to visit China. Prof. Zhijiang Zeng hosted our visit. Yves and I stayed in the same hotel for about 13 nights (April 10 – 22).
I had in mind to see how far mites can go to change their surface chemicals — the chemicals that insects often use for recognition. Honey bees, for example use these chemicals to distinguish who are their hive mates. In the case of honey bee workers, it seems the smell is a combination of genetics (from father and mother) but also smells from the environment, forming a “Gestalt” of odor.
In the case of the notorious varroa mites, we know that they can change their surface chemicals to match the developmental stage of their hosts: a mite will smell more like a pupae if the host is at the pupae stage, and more like an adult bee when the bee is ready to emerge. I thought perhaps we can challenge the mites to see if they could smell like a honey bee of an entirely different species? Nobody has done this before and this can be challenging. For one thing, it took me several years to find varroa mites on the Asian honey bee, Apis cerana (Ac). So we thought we will just transfer mites from A. mellifera (European honey bees, the only species introduced in North America, Am) to Ac and see if mites will change their smell to the new host. We got lucky and found mites on A. cerana! So we did both transfers: Ac to Am and Am to Ac.
Of course we need to have controls, so some mites remained on their original hosts, Ac or Am, but still transferred to control the handling and experimental conditions.