The Curious Beekeeper

July 2014

Sampling for Pesticide Residues, Part 1:

Deciding What to Sample

Pesticide Research Institute


After the large bee kill in almonds this spring, many beekeepers were interested in finding out more about what role pesticides might have played in the losses. In this installment of The Curious Beekeeper, we provide some guidance on sampling for pesticide residues, with a focus on what type of sample should be taken, either from inside the hive or from the environment in which the bees may have been exposed. We also provide perspective on the advantages and disadvantages of the different sample types. In a subsequent article, we’ll talk more about the actual logistics of sampling, analysis, and interpretation of results.

Why Take Your Own 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 were responsible for the kill. The results could also indicate that the hive failure was unrelated to pesticide use, which allows the beekeeper to focus on other possible causes.

If you have reported a bee-kill incident to your local Agricultural Commissioner or Department of Agriculture’s enforcement office (the State Lead Agency), they will want to take their own samples. In general, enforcement staff will not use samples taken by beekeepers for enforcement actions. However, if they cannot visit the apiary until a week or two after the incident, it is possible that the pesticides that affected the bees will have already been degraded by microbes, sunlight and oxygen, especially in hot weather, and the results may not provide an accurate accounting of the pesticides that caused the damage. The best approach in this case is to take samples as soon as you notice something wrong and store them in the freezer until they can be analyzed. At a minimum, take a frame containing pollen from one of the affected hives, place it in a plastic trash bag and put it in the freezer. If the State Lead Agency staff also takes samples, you will both have a point of comparison.

Another reason to take your own samples is that you can 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.

In any event, it is critical to take samples as soon as you notice a problem and get them into a freezer as soon as possible.

What to Sample?
You go out to check on your apiary and find many dead bees on the ground in front of the hives, with some of them still alive, but twitching and spinning on the ground in front of the hive. Pesticides are a likely suspect. The question is, what do you sample—Bees? Pollen? Wax? Honey? The plants that were sprayed? In an ideal world, you would be able to sample all of the above, but with each sample costing over $300 to run, some choices usually must be made.

Bees: 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 as soon as possible, preferably while they are still alive and twitching in front of the hive.

There are several disadvantages that make bee samples not the