Pesticide sample analysis has been part of the National Honey Bee Survey since 2011. Every year, a few lucky beekeepers from each participating state are selected to have their apiary sampled and tested for in-hive pesticides. Once we receive the samples from the state apiary inspectors, we then prep, package and ship them to the USDA AMS National Science Laboratory in Gastonia, NC. They’re the gold-standard in agricultural pesticide analysis, and they screen each of our samples for 200 pesticides that are currently being used in the US (the list is updated frequently).
The type of sample collected for pesticide analysis has changed throughout the years. From 2011 to 2017, states collected bee bread. From 2017 to 2019, the states collected wax from brood frames. Most recently, in 2020, we switched back to bee bread.
It’s not a surprise that one of our most frequently asked questions we receive is this: Why did you change screening for pesticides from bee bread to wax (and vice versa)? What is the difference?
Bee bread is a mixture of pollen and nectar or honey, made by honey bees because they cannot digest fresh pollen directly. When nurse bees consume it, it allows them to produce royal jelly that they then feed to the developing brood. Pesticide contamination of bee bread could occur in either its creation or storage of the final product, but the highest risk of pesticide contamination most likely occurs in the ingredients: the pollen and nectar collected by foragers. Bee bread can be a little tricky to differentiate from fresh pollen for beginners, so here’s a diagram of how to identify it.
Pesticide analysis of bee bread is preferred for identifying immediate or current pesticide exposure events, akin to a snap-shot of what pesticides are or shortly were in the apiary at the moment the sample was taken. In the first years of the survey, fewer samples were taken; but still, most of the pesticide sample data collected has been from bee bread samples (1,078 total).
Percent of bee bread samples with 0 pesticides: 17.9% (193 samples)
Highest number of pesticides in a bee bread sample: 21 pesticides
Median number of pesticides in a bee bread sample: 2 pesticides
Average number of pesticides in a bee bread sample: 3.4 pesticides
Beeswax is the foundation of a hive and is produced by small pores on bees’ abdomens. They chew the tiny flakes of wax until they become soft and then use it to form the hexagonal cell comb. Honey bees store their food in these cells, the queen lays her eggs in them, and the brood grows within them too. Honey bees reuse their wax architecture indefinitely, and it makes sense that they do because it is biologically expensive for a colony to produce. Making wax burns a lot of energy, and the workers eat a lot of nectar and honey in order to produce it.
As you can imagine, after years and years of bees recycling their wax, the comb can become quite dirty. Brood wax in particular turns dark in color—brown or even black—in contrast to honey comb, which has that pretty shade of yellow-white. Brood wax turns dark because developing brood shed their cocoons during metamorphosis and make waste in it (yup, they poop in it). Also, most pesticides are lipophilic (meaning they have a tendency to seep into and combine with lipids), so if the wax comes into contact with a pesticide at any point (through stored pollen, bee bread, or nectar), it has a tendency to stay there for a long time. Because the pesticides linger in the wax for so long, these samples are much higher in detected pesticides than the bee bread samples (see histogram below).
In contrast to bee bread pesticide analysis, which is a real-time “snap-shot” of an apiary’s pesticides, performing a pesticide analysis on wax is best suited for researchers who wish to know a historical record of pesticide exposure. Taking wax samples is fairly new to the survey; we have 881 records so far. Wax samples require an extra step for homogenization. They must be frozen using liquid nitrogen, making them extremely brittle, which allows them to be pulverized into crumbles and powder.
Percent of wax samples with 0 pesticides: 0% (0 samples)
Highest number of pesticides in a wax sample: 38 pesticides
Median number of pesticides in a wax sample: 12 pesticides
Average number of pesticides in a wax sample: 14 pesticides
On average, we have found fewer pesticide detections in bee bread vs. wax samples. We have also found a higher percentage of fungicides present in wax in compared to bee bread. This is likely due to the difference in sample material: pesticides don’t “hang around” in bee bread as well or as long as pesticides do in wax. Bee bread analyses are preferred for identifying immediate or current pesticide exposure events; however, wax pesticide residues are more indicative of a long-term record of exposure. To better understand how honey bee health is affected by pesticides, the survey will periodically switch from one type of sample to the other to capture both exposure routes.