My readers let me get away with nothing; every statement I make is followed by another question. And that’s a good thing, the very best part of a blog.
After reading my post on pheromones, Mark from New York wanted to know if the attraction between a Varroa mite and a honey bee larva is mediated by a pheromone. Excellent query.
By definition, a pheromone is a chemical or mixture of chemicals that is released by an individual and affects the behavior or physiology of another individual of the same species. In other words, the action is intraspecific.
It follows that chemicals that affect individuals of a different species require a different word, and there’s nothing a scientist likes better than another obscure word. Right?
Another kind of attraction
So alas, we have the word kairomone. It just so happens that I keep A Dictionary of Ecology, Evolution and Systematics by Lincoln, Boxshall, and Clark (1998) on my desk. The entry for kairomone reads:
An interspecific chemical messenger, the adaptive benefit of which falls on the recipient rather than the emitter; an olfactory chemical used by parasitic or predatory insects to locate their hosts or prey.
This definition fits perfectly. Varroa destructor and Apis mellifera are different species, and the Varroa mite (the recipient) uses an odor produced by the honey bee (the emitter) to its own benefit. The parasitic Varroa mite uses the odor to find a host.
Kairomones are quite common in the animal kingdom. Many examples exist among insects and arachnids, but other examples can be found in prokaryotes, plants, and even vertebrates. For example, Bunnell et al (2011) found that an ectoparasitic tick of hedgehogs was attracted by the fecal order of sick (but not healthy) hedgehogs.
Parasites attracted by kairomones
Varroa mites are especially attracted to the odor of nurse bees because nurse bees carry them into the brood rearing area. Once in the brood area, the mites are more attracted to drone brood than worker brood. Research on exactly what chemicals are involved is ongoing and could lead to better methods of mite control in the future.
But Varroa mites are not the only honey bee parasite affected by kairomones. Small hive beetles, for example, pupate in the soil so they need a way to find honey bee colonies. Research indicates that small hive beetles respond to chemicals found in alarm pheromone as well as odors from pollen and beeswax (Torto et al, 2011). Although it’s hard to imagine an organism being attracted to alarm pheromone, it provides a sure-fire way for the small hive beetle to find a home.
Bunnell T, Hanisch K, Hardege JD, Breithaupt T (2011): The fecal odor of sick hedgehogs (Erinaceus europaeus) mediates olfactory attraction of the tick Ixodes hexagonus. Journal of Chemical Ecology 28, 1901-1917.
Torto, B., Suazo, A., Alborn, H., Tumlinson, J.H. and Teal P.E.P. (2005). Response of the small hive beetle (Aethina tumida) to a blend of chemicals identified from honeybee (Apis mellifera) volatiles. Apidologie 36: 523-532.
Honey Bee Suite