Miticide strips interact | Treating bee hives with one chemical, then exposing them to another can increase toxicity to dangerous levels
WINNIPEG — A quick glance at a bottle of Tylenol makes it clear that acetaminophen and alcohol don’t mix because the combination can cause liver damage.
Medical doctors know about the Tylenol-alcohol threat and many other dangerous pharmaceutical combinations, yet little is known about the interaction between the chemicals used to treat bees for parasites and disease, says a University of Nebraska entomologist.
Marion Ellis, who spoke at the annual Canadian Beekeeping Convention in Winnipeg last month, said his research has proven that certain chemicals shouldn’t be used in combination because the insecticide interactions can be deadly for bees.
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He said beekeepers have injected a host of chemicals into beehives to control the spread of varroa mites since the pests became an issue in North America 25 years ago. Products include Checkmite, Apistan, Apivar, Thymol, oxalic acid and formic acid.
Beekeepers don’t use miticides in combination, but Penn State entomologists have found that residues build up in the beeswax, which can cause interactions.
“We’re getting quite the array of things that are there (in the beeswax) and have the potential to interact,” he said. “You have a legacy of what you have done in the past.”
Ellis said a U of N colleague, Reed Johnson, has found that two kinds of miticide strips interact in a negative fashion.
When he treated bees with coumaphos, the chemical in Checkmite, and then exposed the bees to tau-fluvalinate, the active ingredient in Apistan, the fluvalinate became two to 32 times more toxic to the bees, depending on the Checkmite dosage.
It’s difficult to determine in real world conditions how much bees are exposed to coumaphos before a beekeeper treats a hive with Apistan, but Ellis said the Penn State survey indicated both chemicals are present in commercial beehives.
“Fluvalinate was found in 97 percent of the samples, coumaphos in 98 percent of the samples.”
Ellis said the two chemicals interact and become more toxic to bees because of a group of enzymes called P-450. The enzymes, which are found in most living organisms, degrade and eliminate toxins that might otherwise destroy cells inside a human, a rat or a bee.
However, bees have fewer P-450 enzymes than other creatures and are more susceptible to toxins.
“Plants produce a lot of chemicals to prevent insects from eating their tissues, so (plant eating insects), by necessity, needed more of those (enzymes),” Ellis said.
“Pollen and nectar are very low in these (toxic) plant chemicals, so that’s one reason why honeybees are a lot less able to deal with these toxins than other insects and other organisms.”
However, the enzymes also degrade man-made chemicals, which means harmful interactions between miticides are possible.
If the enzymes in bees are detoxifying because of exposure to chemical such as coumaphos, they aren’t available to deal with the introduction of another chemical like fluvalinate.
“The strip continues to release the toxin and it’s not being broken down, so it just builds up and builds up (in the bees),“ Ellis said.
“If (beekeepers are) looking at interactions between miticides… the coumaphos and fluvalinate combination is the one (they) should be most cautious about.”
Although Ellis didn’t say so, Johnson thinks there might be a connection between chemical interactions in the hive and colony collapse disorder, which has destroyed hundreds of thousands of American beehives over the last several years.
Another deadly chemical combination for bees is Group 3 fungicides and miticides.
Ellis has studied Group 3 fungicides applied to orchard and vegetable crops. He said bees should not be treated with miticides if they have been used to pollinate an orchard where trees were treated with a Group 3 fungicide.
“If you pre-treat with prochloraz (a Group 3 fungicide) and then expose them to fluvalinate, the fluvalinate becomes nearly 2,000 times more toxic to the bees,” he said.
“(Therefore, beekeepers) should avoid using P450 detoxified miticidal drugs when bees are likely to be exposed to those Group 3 fungicides.”
