The contribution from pesticides on colony loss has proven difficult to quantify, because exposure does not typically result in sudden death of an entire colony. It is far more likely to cause sublethal effects on individual bees that may go unnoticed. What can be accurately measured, however, is the concentration of residues found in hive products like wax and pollen. The Bee Informed Partnership samples these materials from beehives across the country and presents the results in an annual pesticide report. The data makes for some interesting insights and also raises some important questions.
The first thing to notice is that prior to 2017, pesticide samples were taken only from stored pollen (bee bread). After 2017, they were taken only from beeswax. During 2017, samples were taken from both. The BIP offers no explanation for the transition to a new methodology on their website, which resulted in a rather different representation of the pesticide problem. Have a look at the five most prevalent chemicals found in US-based beehives since the survey began:
What is immediately apparent, and perhaps unsurprising, is that beekeepers are the number one source of pesticide residues found in managed hives. Since 2011, the BIP has detected more than one hundred different pesticides in bee bread and beeswax. Some notable absences include oxalic and formic acid.
For the first six years of the survey, a degradation product of amitraz known as 2,4 DMPF was the most prevalent pesticide residue found in samples of stored pollen. Amitraz is the active ingredient in Apivar and has been portrayed as a hive-friendly miticide after early research failed to detect residues. It has since been shown to be very unstable in the acidic environment of a beehive and quickly breaks down into several metabolites, some of which are more toxic than amitraz itself (Korta 2001). A staggering 71% of wax sampled since 2017 has tested positive for amitraz residue.
The most prevalent residue found in comb comes from coumaphos, the active ingredient in Checkmite. Fifth highest is fluvalinate, the active ingredient in Apistan. What’s interesting is that both products have practically become obsolete. They were very effective varroa treatments twenty years ago, but overexposure quickly resulted in the development of resistance by the mite. Like most synthetic options, coumaphos and fluvalinate are highly lipophilic and have long-term stability in beeswax. Their lingering presence reflects widespread use of old brood combs and the manufacture of foundation using contaminated wax. These poisons readily migrate through combs and into food stores via transfusion through the cell wall. They can also be spread by foragers to untreated hives within drifting distance (Bajuk 2017). Melting and processing the wax does not neutralize or remove these pesticides (Jimenez 2005).
While some toxins have been discovered by the BIP at levels that exceed established tolerances, such limits lose relevance when the pesticide remains stable in the environment. Even trace amounts can produce unknown toxic effects upon interaction with other chemicals. Blending pesticides can elevate their toxicity, and such synergistic effects have already been documented in coumaphos and fluvalinate (Johnson 2009). Their residues have also been detected repeatedly in new foundation, meaning many hives are likely to be contaminated with a toxic blend of pesticides even before they contain any bees. The extent of this risk is difficult to know but likely to be high, considering 75% of wax sampled by the BIP contained between nine and thirty-eight different pesticides. None of the samples have been found to be pesticide-free.
Only one product from the top five in each column is not applied by the beekeeper. Chlorpyrifos was detected in 16% of bee bread samples. This is bad stuff that causes brain and motor impairment in children, particularly those that suffer prenatal exposure. Unsurprisingly, it’s also highly lethal to honey bees, as are most insecticides. Application of chlorpyrifos has been banned in the United States for residents but is still applied extensively on commercial crops, including the highly visited blooms of oranges and almonds. It is the apparent opinion of regulatory agencies that just because chlorpyrifos is unsafe for residents to apply does not mean residents should not be exposed to it. Gratefully, this perverse line of thinking was successfully challenged, and in August 2018 a federal appeals court ordered an outright ban on chlorpyrifos. The ruling is currently on hold and under appeal by the administration.
The most prevalent non-beekeeping pesticide detected in wax samples was carbendazim. This deathly chemical has already been banned for use on food stuff in the US, Europe and beyond, but is finding its way into apiaries across the country. Although carbendazim is only approved for use in paints and adhesives, it is also the primary degradation product of an approved and widely used pesticide called thiophanate-methyl. This fungicide is applied to almonds and many other pollinated crops. In terms of human exposure, the EPA describes thiophanate-methyl as having “low acute toxicity” yet is “classified as a probable human carcinogen.” (EPA Registration Eligibility document). Now, I am not a neurosurgeon, but any chemical found likely to be a direct cause of cancer is considered highly toxic in my house. Further, elements of the reproductive system are known targets of this chemical monster, which has been shown to basically fry the testicles of lab rats. It’s scary to imagine what becomes of the family jewels if exposed to a “moderately” toxic chemical. Carbendazim was detected in 83% of wax samples.
Beeswax appears to harbor more chemicals than bee bread, so perhaps wax sampling allows for a more accurate portrayal of the pesticide problem. It is notable that wax is not a food product. Pollen, on the other hand, has a considerable presence in any worthwhile jar of honey, partly due to the contamination of honey by bee bread during extraction. Partners that compose the BIP include commercial growers whose livelihood depends on the use of pesticides. Publishing an annual report detailing the presence of these poisons in edible hive products is begging for a crisis. These residues are not restricted to trace amounts. Chlorpyrifos has a tolerance on food products of 100 ppb but was found at concentrations as high as 303 ppb in bee bread! For carbendazim, any residue at all is illegal, save for a list of exempted foods that does not include pollen or honey. The BIP detected carbendazim in bee bread samples at an average concentration of 68 ppb. For context, the US has refused shipments of imported orange juice due to detection of carbendazim above 10 ppb.
By the way, where are the neonicotinoids? The most widely used is imidacloprid, which is also the most commonly occurring neonic residue found in beehives. In the case of both pollen and wax, less than 3% of samples tested positive for the pesticide. All other neonicotinoids were found less frequently or not at all. If these products are killing forty percent of colonies, it seems forty percent of samples would contain residue. It’s not even close but maybe it’s also not that simple.
If I’m not alone, the variety and concentration of pesticides being found in our hives is much higher than imagined. In the beekeepers’ defense, varroa is a formidable pest. The massive value of commercial pollination will presumably maintain miticides as the primary hive pollutant for the foreseeable future. The use of organic acids, when appropriate, will help a lot. The biggest thing beekeepers can do to drastically reduce pesticide exposure is rotate combs every three years. Beeswax is clearly a final destination for a wide array of environmental toxins. The threat to human health is reason enough to keep wax fresh, as is the threat to bees. Forcing colonies onto brood combs older than three years reduces longevity, limits colony growth and increases susceptibility to disease (Wu 2011, 2012). On young comb the colony will rear more brood, grow larger populations and increase their honey production (Taha 2019). It’s an easy, practical fix and everybody wins, even those that shouldn’t.
Study of Acaricide Stability in Honey. Characterization of Amitraz Degradation Products; Korta 2001
Coumaphos residues in honey, bee brood and beeswax after Varroa treatment; Bajuk 2017
Residues of organic contaminants in beeswax; Jimenez 2005
Synergistic Interactions Between In-Hive Miticides in Apis Mellifera; Johnson 2009
Pesticide exposure in honey bees results in increased levels of Nosema; Pettis 2012
EPA Registration document: Thiophanate-Methyl; 2005
Sub-lethal effects of pesticide residues in brood comb on worker honey bees; Wu 2011
Honey bees reared in brood combs containing high levels of pesticide residues…; Wu 2012
The relationship between comb age and performance of honey bee colonies; Taha 2019