Varroa mites are responsible for the deaths of millions of honeybees all around the world. They latch on to both adult and developing bees and suck their insect blood, weakening them and causing the colony to collapse during winter. Only able to reproduce inside bee hives, how do the mites manage to go about undetected when surrounded by their host? The answer: smell like them.
New research, led by Michigan State University, has found that the Varroa mite is able to mimic the normal scent of bees, allowing them to infiltrate the hive undetected. Due to the highly social nature of honeybees, and the different levels of hierarchy within the colony, this is quite an impressive feat.
Originally found on the Asian honeybee, Varroa mites started to parasitize the European honeybee when they spread to the west in the 1950s. Since then, they’ve been implicated in the colony collapse disorder that has been sweeping the apiological world and laying waste to hives not just in Europe but also across the Atlantic in America. The mites feed on the insect’s version of blood, called hemolymph, making the bees and the larvae more susceptible to viruses and infection. In their weakened state, the hives often die during winter.
“The mites from Asian honeybees, or the original host, are more efficient in mimicking both Asian and European honeybees,” explained Zachary Huang, lead author of the paper published in Biology Letters. “This remarkable adaptability may explain their relatively recent host shift from Asian to European honeybees.”
Lots of insects trick their host by smelling like them. The caterpillars of the Alcon blue butterfly are particularly good at deceiving Myrmica worker ants by smelling like their young. The ants then pick the caterpillars up thinking they’re long lost larvae and take them back to the protection of their nest. The ants then preferentially feed the caterpillars, even over their own young.
But back to the mites. Being able to copy the smell of the bees is not that straightforward. That’s because they don’t just have to fool one insect, but potentially tens of thousands. Not only that, but the hive is also divided into a complex caste system, meaning that the mites have to trick a whole society in order to succeed. They manage this feat by not just smelling like a general honeybee, but by tailoring their scent to that of the individual colonies.
By tweaking the compounds found on their surface, in this case hydrocarbons, the mites are able to produce the right smell for the right colony. The researchers were able to show that the invading insects were able to alter these compounds not over generations, as was expected, but within days. This new finding helps to explain how the mites have been able to adapt so quickly to different species of honeybee, and how they’ve been so successful.
Main image credit: Gilles San Martin/flickr CC BY-SA 2.0