Behavior Modification of Paralyzed Honeybees
Perhaps the most significant finding made by the SFSU researchers was that honeybees parasitized by Apocephalus borealis display a disrupted circadian rhythm (the physiological “clock” inside most organisms that tells them when it is day and night and whether or not they should be active during those times), leading them fly away from the hive at night to forage instead of during the day.
Behavioral modification of a host by a parasite or pathogen is not a new phenomenon. However, the behavior usually manifests as an uncontrollable urge to move to a location that benefits the parasite by maximizing its potential for dispersal to infect new hosts.
This type of behavioral modification has been demonstrated with fungi, viruses, flukes and nematodes that attack insects. If the behavior of the bee is being specifically manipulated by the activity of the fly larvae, what is the adaptive advantage for the fly to cause the bee to fly off into the dead of night (pun intended)? Insects parasitizing other insects more often opt to simply paralyze the host while their offspring develop within.
A tantalizing alternative proposed by the authors of the SFSU study is that the change in the behavior in honeybees is not actually induced by the larvae but is a result of the bees detecting and reacting to the presence of the parasite themselves.
It remains unclear based on the current research whether the parasitized bees are leaving the hive on their own to prevent their nestmates from being parasitized, or if uninfected bees are detecting and expelling the infected bees for the sake of the hive. Infection of honeybees by some pathogens has been shown to alter the chemicals of the exoskeleton, a change in the “smell” of the bee that is detected by its nestmates, leading to its expulsion from the hive.
Honeybee Parasite Affecting Colony Collapse Disorder
It seems more than coincidence that: 1) CCD has largely been restricted to North America; 2) North America is the geographic range of the fly; and 3) honeybees were only introduced to North America 390 years ago.
With the number of researchers and beekeepers working and studying honeybees since then, this host-parasite interaction is unlikely to be an oversight and likely represents a completely new and relatively recent host shift. In any event, the discovery of this parasite and its unusual effect on the foraging behavior of affected honeybees partially explains one of the most baffling and previously unexplained aspects of the disorder—hive abandonment.
Brown, B.V. Taxonomy and Preliminary Phylogeny of the Parasitic Genus Apocephalus, Subgenus Mesophora (Diptera, Phoridae). (1993). Systematic Entomology 18: 191–230.
Core, A., Runckel, C., Ivers, Quock, C., Siapno, T., DeNault, S., Brown, B., DeRisi, J., Smith, C.D. and Hafternik, J. (2012). An emerging threat to honey bees from parasitic phorid flies. PLoS ONE 7(1): 1-9. Accessed January 4, 2012.
Libersat, F., Delago, A., and Gal, R. Manipulation of Host Behavior by Parasitic Insects and Insect Parasites. (2009). Annual Review of Entomology 54: 189-207. Accessed January 4, 2012.