Friday, February 17, 2012

Colony Collapse Disorder

         Our class recently read this article about queen bee versus worker bee differentiation in honeybees. Of course, if any of us were given the choice we'd all be queen bees: after all, they live longer, bear offspring, and perhaps most importantly, don't have to leave the hive and work. But, North American honeybees are facing a problem right now of too few workers, rather than too few queens (will need to be rephrased for sure). Colony Collapse Disorder (CCD) is characterized by hives having a live queen, honey stores, and immature bees, but all adult worker bees have left. CCD was first reported in the US in 2006, and has remained a problem ever since. Even more interesting, despite extensive research the causative agent is unknown. Many potential causes and risk factors have been identified, but there is widespread disagreement over which is most important. Four main areas are being heavily researched: parasites, pesticides, and management practices.

         Parasites are an attractive explanation, because hives that displayed CCD can be irradiated and reused without a reoccurence of CCD in the new colony. Treatment would also be much simpler if parasites were the cause, because beekeepers could just either use resistant strains of bees, or treat all the hives for that one pesky parasite. However, parasite infections such as the invasive bee mite Varroa typically leave dead adult bees in the hive, and in CCD adults just mysteriously disappear instead of showing up dead. Israeli acute paralysis virus has also been marked as a possible cause after a 2008 study showed a strong correlation between the virus and hives with CCD. Their methods later came under fire and the virus was revealed to have been present in the United States since 2002 at the latest, so Israeli acute paralysis virus is no longer touted as the single definitive answer. Instead, researchers are now looking for the combination of Israeli acute paralysis with other factors, like pesticides.
        Pesticides alone are probably not the answer, since the ones currently in use around hives have been carefully tested to make sure they don't kill honeybees. However, pesticides might be changing the host-pathogen dynamics in more subtle ways. A study used imidacloprid, a common pesticide, in sub-lethal doses to treat three different generations of honeybees, and then challenged these treated bees with Nosema, a gut parasite. The treated bees showed no ill effects from the imidacloprid, but had significantly higher levels of Nosema than the nontreated. There's also evidence that two pesticides used to treat the Varroa mite actually act synergistically together to harm bees. This finding flips the conventional wisdom of "safe" pesticide levels on its head, and underlines the importance of looking beyond simple mortality.
        Management is perhaps the epitome of integrative thinking to CCD. This can cover everything from which pesticides a beekeeper applies, what plants they make available for bee nutrition, and non-chemical bee pathogen control. A big cause of concern has been the practice of moving hives around the country. Because bees are essential for pollinating crop plants, beekeepers can make a killing by renting out their hives to farmers for a certain amount of time each season. However, it stresses the bees to be loaded onto and off a truck, acclimate to a different habitat, and then do it all over again. Beekeepers are counseled to limit their hive transportation,  but it's unclear how successful this has been, as CCD increases demand for pollinators, and they aren't sure how much/if bee transport is contributing to CCD. Breeders have also successfully created Varroa mite resistant strains of bees which are being used right now. Using varroa-resistant strains means less insecticide application also, which separate from Varroa itself looks like it will help decrease CCD.
        Of course, the final alternative has simply not been considered or researched at all: maybe the worker bees have decided to collectively thumb their noses at that lazy queen and head to Cancun.

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