28 September 2012

Honey Bees Adapt And Evolve To Reduce Infection of Parasitic Mite, Varroa Destructor

Colony Collapse Disorder (CCD) is a serious problem plaguing beekeepers. Honeybee hives seem to die out for no apparent reason. Factors suspected to cause colony collapse disorder range from pesticides, climate change, and even electromagnetic waves.

With colony collapse disorder, the economic and agricultural damage it causes run up to billions of dollars. About 30% of the global food supply rely on the honeybees through pollination. Crops such as almonds, blueberries, watermelon, and apples are just few that heavily rely on honeybee pollination. And with beehives dying it out by the thousands year in and year out, scientists are scrambling to find a solution to this problem.

One prevalent factor that is gaining attention and long suspected to be a factor for CCD are parasitic mites. These are small insects that feed off on the honeybee, living inside it and even laying eggs on the eggs of the bees (larvae) or the bees themselves.

One reason that parasites may cause CCD is because a honeybee hive would normally die out because the queen bee has died. But with CCD, the queen bee is still present and the bee eggs are left unattended. Honeybees never leave the hive when there are bee larvae still present.

Although scientists have one time or another zeroed in on a valid reason for CCD, further research have failed to recreate and duplicate any observed findings. This leaves CCD an open mystery up to now.

Honey bees fight back against Varroa

The parasitic mite Varroa destructor is a major contributor to the recent mysterious death of honey bee (Apis mellifera) colonies. New research published in BioMed Central's open access journal Genome Biology finds that specific proteins, released by damaged larvae and in the antennae of adult honey bees, can drive hygienic behavior of the adults and promote the removal of infected larvae from the hive.

V. destructor sucks the blood (hemolymph) of larval and adult bees leaving them weakened and reducing the ability of their immune systems to fight off infections. Not that honey bees have strong immune systems in the first place since they have fewer immunity genes than solitary insects such as flies and moths. These tiny mites can also spread viral disease between hosts. This double onslaught is thought to be a significant contributor to Colony Collapse Disorder (CCD).

Video: Colony Collapse Disorder (CCD)

But all is not lost - honey bees have evolved a way to fight back: hygienic behavior where diseased or parasitized larvae are removed from their brood cells, and Varroa-sensitive hygienic behavior which they use to reduce the number of reproductive mites on remaining larvae.

To find exactly how bees respond to hive infections, researchers from Canada looked at the natural behavioral of bees in the presence of damaged larvae and compared this to protein differences in the larvae and adults. After scanning 1200 proteins the team found that several proteins, including LOC552009 (of unknown function but similar to ApoO), found in the antennae of adults were associated with both uncapping brood cells and the removal of larvae. Other proteins were involved in olfaction or in signal transduction, probably helping the adults find infected larvae amongst a brood.

In damaged larvae, transglutaminase, a protein involved in blood clotting, was upregulated, which appeared to be a key component in regulating the adult's behavior. Other proteins indicated adaptations to help fight infection, including chitin biosynthesis and immune responses.

Dr Leonard Foster from CHIBI at the University of British Columbia, who led this research said, "Bee keepers have previously focused on selecting bees with traits such as enhanced honey production, gentleness and winter survival. We have found a set of proteins which could be used to select colonies on their ability to resist Varroa mite infestation and can be used to find individuals with increased hygienic behavior. Given the increasing resistance of Varroa to available drugs this would provide a natural way of ensuring honey farming and potentially survival of the species


BioMed Central
The Centre for High-Throughput Biology (CHIBI) at the University of British Columbia
Genome Biology
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