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October 2014

Amitraz: Red Flags or Red Herrings?


A number of findings regarding the miticide amitraz (as well as the neonicotinoid insecticides) have come to my attention in recent months. The question is, are they red flags, or red herrings?


A Red Flag?
A couple of weeks ago a beekeeper emailed me a blog with explosive implications. It was written by Penn State entomologist Dr. David Biddinger for tree fruit growers, but may help us to connect the dots between beekeeper complaints of problems with agricultural insecticides (neonicotinoids specifically), beekeeper-applied amitraz, and colony and queen losses. He wrote:

The second special situation where spraying fungicides during bloom can cause problems is where the honey bee keepers are using the insecticide/miticide amitraz for control of varroa mites in the hive. Most tree fruit growers will remember amitraz as Mitac which was used heavily for pear psylla control in the past. This product was routinely used for synergizing organophosphate and pyrethroid insecticides in crops like cotton where key pests had developed resistance, because it shut down the enzymes insects used to detoxify pesticides. This raises concerns about amitraz being used to treat mites in honey bee hives. While it may be effective in controlling varroa mites now that they have quickly developed resistance to the organophosphate coumaphos and the pyrethroid fluvalinate, adding this synergist to a hive basically shuts off a bee’s immune system to pretty much any pesticide with which it later comes into contact.

Oh…my…gosh! Go ahead and read it again! Have beekeepers inadvertently been synergizing (multiplying) the negative effects of miticide residues and agricultural chemicals in hives by their applications of amitraz?
Note: This article is a condensed version of a much more detailed article available at my website.


Or a Red Herring?
Let me assure you, despite its faults, I am not writing this article to trash amitraz; indeed, I encouraged the manufacturer of Apivar® to bring that excellent product to market. In defense of amitraz, let me make perfectly clear that I know of a great many beekeepers who would likely not be in business today were it not for amitraz. And many of them have not suffered from exaggerated colony loss; indeed, some of them are major almond pollinators, as well as being suppliers of queens and packages to the rest of the industry. Based upon that on-the-ground evidence, one might be tempted to let amitraz off the hook, but upon closer look, the story grows more complex.
Amitraz has a long history of successful use as a varroacide. It was yet another Silver Bullet—a treatment or two a year kept mites under control, and the active ingredient didn’t show up in honey. Those in some European countries have used Taktic for decades, and a number of U.S. beekeepers have (illegally) applied it to their colonies since the 1990’s. But things are about to change in the U.S….

For those who haven’t heard, the registration of Taktic in the U.S. has been voluntarily withdrawn by the registrant (Fig. 1).

The loss of Taktic has the potential to seriously shake up the commercial bee industry. Any number of beekeepers have told me that they can’t imagine how they could stay in business without it. That statement has credibility when you consider that when Taktic was temporarily unavailable a couple of summers ago, that a number of beekeepers lacking a “Plan B” simply let their colonies go without treatment, often with disastrous results.

Practical consideration: on the other hand, the illegal use of Taktic has given those same beekeepers an unfair competitive advantage over those of us who stick with the more expensive registered treatments, yet must still compete with the scofflaws in the open market for pollination services and honey sales.

However, there is now an alternative and legal way to apply amitraz—in the form of Apivar® strips. Beekeepers used to fast-acting treatments with Taktic may need to adjust their mite management schedules due to the slower knock down of mites by Apivar. Apivar is designed to be an extended-release treatment that paralyzes the mites to the extent that they are unable to reproduce; the strips are designed for a full 42-56-day treatment. An additional benefit to the strips is that one avoids introducing the additional bee-toxic adjuvants present in the formulation of Taktic—Frazier found that “the miticide formulation Taktic was four times more orally toxic to adult honey bees than the respective active ingredient amitraz.”

Practical note: if you are used to applying Taktic in fall for a quick knock out of mites prior to the formation of the winter cluster, you may be disappointed by the slower results from Apivar. Research from Saskatchewan suggests that in areas in which winter comes on quickly, spring treatment may be the better option.

People put their trust in our governmental regulatory agencies to protect us from harmful foods, medicines, and pesticides. Few take the time to deeply investigate the potential down sides to exuberantly-advertised off-the-shelf medicines or treatments. But the truth is, that we beekeepers should practice due diligence by doing our homework about the things that we put into our hives.

The last thing that I wish to do is to be alarmist, but the rest of this article will deal with possible side effects from amitraz.

One thing that we’ve learned in recent years is about the “legacy effect” of miticide residues in our combs. One reason that beekeepers favor amitraz is that it is nearly insoluble in honey, and the small amount that does dissolve quickly breaks down, mainly into DMPF, which remains stable in honey for at least 45 days. Amitraz is far more soluble in beeswax, where it completely degrades within a day, also mainly into DMPF, which remains stable for a considerable period of time.

A Red Flag?
Although amitraz is considered to be “relatively non-toxic to bees,” chronic exposure of bees to its degradation product in the combs and honey allows for the distinct possibility of it exerting sublethal or behavioral effects upon the bees, or the possibility of synergizing the sublethal effects of other contaminants. So how prevalent is amitraz contamination of combs?

By the year 2003, commercial hives were already so contaminated by amitraz, that there was concern about varroa having developed resistance. Later in the decade, Mullin (2010) detected DMPF in fully 60% of beeswax samples and 31% of beebread samples. Even more recently, DMPF was the third most common pesticide residue in the 451 samples of beebread analyzed by the USDA National Survey from 2010 through January 2014 --present in 23% of samples, led only by the other miticides fluvalinate and coumaphos. By comparison, the neonicotinoids imidacloprid, thiamethoxam, clothianidin, and thiacloprid were found in only 2.9%, 2.4%, 2.2%, and 0.7% of samples, respectively.

Practical application: although one’s honey may test free of amitraz, in fact it is the DMPF that exerts its toxic action upon honey bees. Testing shows that DMPF is an extremely common contaminant of commercial combs.

Or a Red Herring?
So let’s do some math! Using the formula for the Daily Consumption Hazard that I proposed in a previous article, and using the published LD50 values for amitraz, I calculate that a bee consuming even the most highly contaminated pollen would only get a tiny fraction of the lethal dose. On the other hand, the contact dose that bees might get from rubbing against highly-contaminated comb might approach the range of lethality.

However, that doesn’t necessarily mean ...