[The second in my guest post gig over at Scientopia]
I spent my first post lamenting confusion over CCD (Colony Collapse Disorder), honey bees, and native bee species. One key problem is that CCD as described by entomologists is not the same as “disappearing bees” as described by media or Hollywood. (Although, to be fair, “vanishing bees” is a pretty cool idea, suggesting that perhaps aliens have decided to abduct bees rather than rednecks in pickup trucks, just to mix things up a little.)
CCD is a syndrome. By definition, a syndrome is a collection of signs and symptoms known to appear together but that have no known cause. Unfortunately, we can’t use Koch’s postulates to clearly link a causal pathogen to a disease.
- “the apparent rapid loss of adult worker bees from affected colonies as evidenced by weak or dead colonies with excess brood populations relative to adult bee populations;
- the noticeable lack of dead worker bees both within and surrounding the hive; and
- the delayed invasion of hive pests (e.g., small hive beetles and wax moths) and kleptoparasitism [honey stealing] from neighboring honey bee colonies.”
To diagnose a hive that is in the process of failing:
“In those CCD colonies where some adult bees remained, there were insufficient numbers of bees to cover the brood [brood = baby bees], the remaining worker bees appeared young (i.e., adult bees that are unable to fly), and the queen was present.
Notably, both dead and weak colonies in CCD apiaries were neither being robbed by bees (despite the lack of available forage in the area as evidenced by the lack of nectar in the comb of strong colonies in the area and by conversations with managing beekeepers) nor were they being attacked by secondary pests (despite the presence of ample honey and beebread in the vacated equipment).”
“Bees gone” is not sufficient for a diagnosis of Death by CCD, if you are a CSI Apiarist. The status of the brood is important. A lot of hive health is assessed by how well the queen and her minions are producing and caring for the young.
Another major complication is that beekeeping is an endeavor with an incredibly high rate of failure. It boggles my mind that 15% hive loss yearly is NORMAL. I don’t mean hive losses from CCD–that’s the rate of hive failure before CCD arrived on the scene. It’s just the cost of doing business–a lot of hives don’t make it through the winter.
In the last decade, that loss rate has crept up to 30%, on average, for the US. This increase in bee deaths has been primarily driven by two bee parasites–Varroa Mites and Tracheal Mites. Varroa mites are pretty big, compared to a bee. It’s probably like having a tiny vampiric chihuahua stuck to your body. Here, have a look:
(Also, I just SERIOUSLY creeped myself out imagining vampire chihuahuas.)
Tracheal mites live in the breathing tubes of insects, and as you might expect, severely inhibit the ability of bees to thrive. And I’m just getting started on things that kill bees independently of CCD. I can think of at least 20 different fungal infections, viruses, and additional parasites. Foulbrood. Nosema. Chronic Paralysis Virus. I’ll spare you the full list, but a LOT of things like to kill bees.
This is part of what makes teasing out the cause of CCD so difficult. It’s not that there are no smoking guns; there are hundreds of smoking guns, all of which plausibly contribute to the decline of bees. Here is the short list of contributors to CCD, ordered roughly in order of importance, based on the most recent literature:
- increased losses due to varroa mite;
- diseases such as Israeli Acute Paralysis virus and the gut parasite Nosema;
- pesticide poisoning through exposure to pesticides for in-hive insect or mite control
- habitat loss for foraging; inadequate forage/poor nutrition;
- Exposure to pesticides in the environment (including neonicotinoids)
- poor nutrition and migratory stress brought about by the increased need to move bee colonies long distances to provide pollination services.
Note that the pesticides on this list that are of most concern, and mostcommon in hives, are the ones that we apply to the bees on purpose. Miticides and fungicides to control parasites and diseases of bees are the ones of most concern for sub-lethal effects on the bees we are trying to protect.
Bees encounter pesticides in their environment as they look for nectar and pollen, and those get all the press. That story fits a narrative for humans–we fear pesticides in our environment too–and gets privileged over other factors in news coverage.
What pesticides really seem to do is make everything else worse for bees. For example, three different studies this year found that exposure to pesticides increased Nosema infections. It’s these synergistic effects that make pesticides of concern, not their ability to kill a bee outright.
Many of these historic collapses pre-date the introduction of pesticides or other modern bee culture practices that are being blamed for bee losses today. The extent of some of those historic losses are staggering–up to 90% colony collapse in some cases.
Hopefully, this gives you a sense of just how difficult and tangled the problem of CCD is, and how very far we are from a simple linear cause –> effect relationship for this problem. It IS hard out there for a bee. And it’s frustrating that when researchers find a new potential contributor, it’s reported as “the cause” of CCD, even when the scientists involve explicitly say it isn’t a cause.
We aren’t kidding. It is complicated.
Next up: a brand new literature review published this month that tries to untangle the issue of pesticides and bees.