Sampling Beehives for Pesticides

This page provides background information on how sampling may help you determine the cause of a colony failure, as well as the timing of sampling. We also describe the different types of samples you can take—pollen, bees, wax, honey, plants, soil or water—and discuss the pros and cons of each. Once you’ve decided what to sample, see our  Bee Sampling: Process and Cost  web page to obtain a cost estimate and arrange for a sample kit and sampling instructions to be sent to you.

Why Take Samples?

If pesticides are suspected as the possible cause of a bee-kill or hive failure, sampling and analysis for a range of pesticide residues will help determine what pesticide or pesticides may have been responsible for the kill. Taking your own samples will enable you to select a lab that will analyze for a wide range of pesticides, with the ability to detect low concentrations. Your local State Lead Agency might have access to a lab that can analyze for only a limited number of pesticides, and/or has limited ability to detect low levels of pesticides. If the pesticide that caused the hive failure or bee-kill is not included in the analysis or the detection limits are too high, the results may be presented as “no pesticides were detected,” and the State Lead Agency would likely dismiss pesticides as a possible cause. But in fact, it may have been that their analysis wasn’t specific enough or sensitive enough to see the pesticide in question.

Taking samples of pesticide residues in your hives serves the important function of documenting actual exposures of honey bees to pesticides. If you choose to contribute your data to PRI’s database of pesticide residues in beehive materials, your participation will enable us to present US EPA with essential data regarding pesticide-related bee kills. This can be done without giving away your identity and risking losing your locations, and it is critical to making changes to protect your bees from pesticide exposure.

When to Sample?

Sample as soon as possible after the kill. Store samples in the freezer until you can process them.

What to Sample?

So you’ve had a bee kill. The question is, what do you sample? Bees? Brood? Pollen? Wax? Honey? The plants that were sprayed? In an ideal world, you would be able to sample all of the above, but with the cost of each sample at over $300, some choices usually must be made. Advantages and disadvantages of sampling the different materials (matrices) are presented below. Use this information to guide your sampling strategy. PRI staff is available for a call if you want to discuss the options further.

It is also useful to have a comparison sample from a healthy colony. The best comparison, if available, is to sample a healthy colony from the same apiary with the failing colonies. However, if one hive in an apiary found some contaminated forage, it is likely that most of the colonies found it, so you may not have a healthy colony in that location for comparison. If you have other nearby locations (within a few miles) for your hives where the bees are doing well, take a sample from a healthy colony in that location.

A bee sample is easy to take, but only provides information on pesticides that the bees were exposed to in the very recent past. Sampling bees is best for very high exposures, such as when bees have foraged on flowers contaminated with dust from the planting of treated seeds that contain high levels of pesticides. For any bee samples, it is essential to sample them and get them into a freezer as soon as possible, preferably while they are still alive and twitching in front of the hive.


  • A bee sample provides information on pesticides that the bee may have encountered very recently.
  • If bees were exposed to sub-lethal levels of pesticides, you may be able to see pesticides that bioaccumulate in the bee. The older miticides coumaphos and fluvalinate are frequently found in bees.
  • Easy to sample.


  • For the highly bee-toxic pesticides, it doesn’t take much to kill a bee, which means that the amount in the bees might be below the detection limits of the laboratory.
  • If the bees are not killed outright and you sample a few days later, the bees may have metabolized most of the pesticide and excreted it or transformed it into different compounds that the lab doesn’t necessarily look for. The net effect is that the amount of pesticide might be below the detection limits of the laboratory.
  • If a sample of live bees is collected from the hive, not all of them may have been exposed, so the results will show an average concentration, not the concentration of pesticide in the exposed bees only.
  • Unless you find the bee kill very soon after it happens, the dead bees on the ground in front of the hive and the pesticides on them will have started to degrade, which means that the amount of identifiable pesticide residue may be below the detection limits of the laboratory.

In general, if you only wish to analyze a single sample, bees are not the best sample to run because of problems with detection limits.

Pollen, as beebread

Sample packed pollen (beebread) if you want to see what the queen and larvae are being fed inside the hive. Worker bees don’t need much protein, so they don’t ingest as much pollen as the queen and the larvae. If the adult bees are not dead, but the brood isn’t hatching or is being pulled dead out of the cells by the worker bees, sampling the pollen may provide some insights into what is killing the bees.


  • Pesticide degradation should be slower in packed pollen (beebread) than in pollen collected in a pollen trap because it is out of the sunlight and packed tightly in the cells, excluding oxygen that could degrade any pesticides present.
  • Relatively easy to sample.


  • Beebread also contains enzymes, honey, and bacteria that ferment the pollen, which may also degrade pesticides. The extent to which pesticide degradation in beebread occurs is not well known, but may play a role in either accentuating or reducing the toxicity of the pollen.
  • Pollen is gathered at different times and it is possible that only one source of pollen will be contaminated. If only one source of pollen is contaminated, it will be diluted by the uncontaminated pollen, possibly reducing the apparent concentration of pesticide to the point where it cannot be detected.
  • The pollen may be contaminated with miticides if they are used to control Varroa. In some cases, the presence of the miticide will make it difficult to detect other pesticides.
  • More time consuming to take the sample compared to bees.
Pollen from a pollen trap

Using a pollen trap on the front of a hive to collect the pollen as the bees bring it into the hive will provide information on pesticide residues in the environment. These samples will not have significant residues of pesticides that were introduced into the hive for mite control.


  • Evaluating pollen from a pollen trap can also improve the sensitivity of the analysis for pesticides that may be masked by those used in mite control.
  • May be easier or faster to collect than packed pollen (beebread).
  • You can be sure that the pollen you’ve sampled was collected at a specific time, so it may be easier to pinpoint the source of potential pesticide exposures.


  • Requires special equipment and planning.
  • May limit pollen supplies for the colony. Don’t leave the pollen trap on for more than a day or so.
  • If the pollen trap is in the sun, pesticides present may degrade in sunlight and heat.
  • Impossible to do if the colony is already dead.
Honey or Nectar

Pesticides that are somewhat water soluble, absorbed systemically by plants, and resistant to degradation are known to occur in nectar.  The neonicotinoid insecticides have these characteristics, as do several common fungicides. When the nectar is evaporated to make honey, pesticide concentrations increase.

Pesticide residue analysis of honey or nectar in the hive will provide a measure of what pesticides were brought into the hive by the nectar-foraging bees, as well as any pesticide residues that may be extracted from the wax cell in which the honey is stored. Although all types of pesticides may be found in honey or nectar from contamination by direct sprays, those typically found include water-soluble “systemic” pesticides that are readily taken up through the roots or leaves of the plant, and miticides used inside the hive.

Contaminated honey may not affect the hive until the bees eat it, which may explain some of the overwintering losses—as bees tap into contaminated honey stores in the winter, they receive a dose of the contaminants, which may be sufficient to destabilize the health of the colony.


  • May be available year-round, even in hives with very little packed pollen (beebread).


  • More difficult and time-consuming to sample than pollen.

A wax sample provides historic information on the fat-soluble chemicals that have been introduced into the hive. Sampling wax will give a clearer picture of chronic (long-term) pesticide exposures your bees experience. Because the brood is reared inside a cell, the pesticides in wax contribute to brood exposures. A Penn State study showed that 98% of wax samples contain fairly high levels of the older miticides coumaphos and fluvalinate.3 The fungicide chlorothalonil and degradates of amitraz (Apivar®) were also frequently detected. However, unless you are specifically looking for fat-soluble pesticides or miticide residues, wax is not the highest priority sample to take.


  • Easier to sample than packed pollen or honey.
  • May indicate exposure during larval development.


  • May not indicate recent pesticide exposures or exposures to the more water-soluble pesticides.

If you suspect that your bees have been killed by a specific application to a nearby crop (or drift from that application), it will be informative to sample both the pollen or nectar the bees were bringing into the hive and the plants on which the bees were foraging to determine if the same pesticide residues are present in both samples. Pesticides present may degrade in sunlight, so gathering samples in a timely manner is important.


  • Sampling the plant material that you suspect may have affected your bees can narrow down the route of exposure.


  • Showing that a pesticide was present in plants nearby does not necessarily mean that your bees were exposed through contact with the crop. Bees may forage anywhere within a few miles of your beehives, but if the crop next-door is a bee-attractive crop, it is likely that at least some of the bees in the hive were foraging in that field. Determining the identity of the pollen the bees are bringing into the hive will ascertain whether or not the bees were foraging on that crop.
  • Sampling plants on private property will require the permission of the owner, which may make plant sampling considerably more difficult.
Soil or Water
Soil and water can be contaminated by pesticide sprays, soil drenches and through the planting of treated seeds. Bees can be exposed to very high levels of pesticides when they drink from contaminated puddles or damp soil. If you suspect this is the case, testing soil or water from these areas will provide some answers.


  • Sampling the soil or water that you suspect may have affected your bees can narrow down the route of exposure.


  • Showing that a pesticide was present in soil or water nearby does not necessarily prove that your bees were exposed through drinking from contaminated soil. Documenting the bees drinking from the affected source with photos or video will provide more conclusive evidence of exposure from that source.

How to Sample

See our Bee Sampling: Process and Cost  web page to arrange for a bee-kill sampling kit to be sent to you, complete with instructions and all of the necessary materials for sampling, along with expert guidance on interpreting the results.


  • Stoner KA, Eitzer BD. 2012. Movement of Soil-Applied Imidacloprid and Thiamethoxam into Nectar and Pollen of Squash (Cucurbita pepo). PLoS ONE 7:e39114; doi:10.1371/journal.pone.0039114.
  • Byrne FJ, Visscher PK, Leimkuehler B, Fischer D, Grafton-Cardwell EE, Morse JG. 2013. Determination of exposure levels of honey bees foraging on flowers of mature citrus trees previously treated with imidacloprid. Pest. Manag. Sci. 70:470–482; doi:10.1002/ps.3596.
  • Mullin CA, Frazier M, Frazier JL, Ashcraft S, Simonds R, vanEngelsdorp D, et al. 2010. High Levels of Miticides and Agrochemicals in North American Apiaries: Implications for Honey Bee Health. F. Marion-Polled. PLoS ONE 5:e9754; doi:10.1371/journal.pone.0009754.
  • Van der Sluijs JP, Simon-Delso N, Goulson D, Maxim L, Bonmatin J-M, Belzunces LP. Neonicotinoids, bee disorders and the sustainability of pollinator services. Current Opinion in Environmental Sustainability; doi:10.1016/j.cosust.2013.05.007.

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