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A seven-year study assessing pesticide residues in bee bread throughout the United States

By May 15, 2021No Comments

Most beekeepers are concerned about pesticides but unsure how concerned they should be.

On the one hand, every commercial beekeeper who rents their bees for pollination of almond, blueberry, apple, or other high-value crops has a story about how some of their colonies have died fairly quickly after one or more pollination events. Given what we know about pesticide exposure during crop pollination, it’s highly plausible those colonies died from harmful exposures.

On the one hand, every commercial beekeeper who rents their bees for pollination of almond, blueberry, apple, or other high-value crops has a story about how some of their colonies have died fairly quickly after one or more pollination events. Given what we know about pesticide exposure during crop pollination, it’s highly plausible those colonies died from harmful exposures.

But if a beekeeper doesn’t do crop pollination, acute problems easily attributed to pesticide exposure are rare. Does that mean pesticide exposure is rare outside of crop pollination? Or, if exposure is common, are the types and levels of pesticides benign enough that they don’t pose an acute risk to bees? What about sublethal risk? Is there reason to suspect normal day-to-day pesticide exposure influences the susceptibility of bees to varroa, nosema, brood diseases, or queen events where an immediate link to pesticides isn’t necessarily clear? These are the topics for our forty-first Notes from the Lab, where we summarize “Pesticides in Honey Bee Colonies: establishing a baseline for real world exposure over seven years in the USA,” written by Kirsten Traynor and colleagues and published in Environmental Pollution [2021].

As most readers of this column are probably aware, there are thousands of published studies showing that when a bee is dosed with a pesticide, a high enough dose will kill the bee. Some readers may also be aware of the more recent literature showing that low doses of pesticides can have important sublethal effects on bees, including impacts on immunity, behavior, and reproduction. But a critically important point is that these studies measure the toxicity of a pesticide, which is only half the equation for understanding risk from that pesticide. We also need to understand exposure. In other words, risk = toxicity x exposure, so we need to understand toxicity and exposure to understand risk from pesticides.

Gaining an understanding of pesticide exposure to bees is difficult for two reasons. First, exposure occurs in many different contexts. For example, you can probably guess that exposure to pesticides will be greater if your hives are in an agricultural region compared to Glacier National Park. But what if you live next to a golf course compared to a small apple orchard? Or what if your hives are in the suburbs compared to a small organic farm? Can you predict in which of those settings your bees will encounter more pesticides? I’m guessing you can’t. I certainly can’t. Which means we need to test a lot of different contexts to fully understand when and where pesticide exposure will occur.

Second, there are currently several hundred different pesticides that are used throughout the United States, and you need to test for all of them (or at least a majority of them) to have an adequate understanding of exposure. As you might guess, that’s expensive. Currently, multi-residue pesticide analyses are about $350 per sample. $350 per sample! That means analyzing 100 samples will cost more than a brand new Ford F-150 (https://www.ford.com/trucks/f150/models/f150-xl/).

Due to these facts, the number of exposure studies that exist is far less than the number of toxicity studies. Thus, when trying to understand risk from pesticides, we’re frequently limited by our knowledge of exposure. To fill this gap, Traynor and colleagues set out to gain the broadest understanding possible of day-to-day pesticide exposure via pollen to honey bees in the United States. Over a period of seven years (2011-2017), they collected 1,055 bee bread samples from apiaries in 39 states and Puerto Rico (Figure 1). Samples were taken throughout the year (January-December) during normal apiary inspections as part of the National Honey Bee Disease Survey (https://research.beeinformed.org/state_reports/). The samples were analyzed for 175 pesticides and metabolites on average. In addition, at a subset of apiaries, hives were assessed for varroa (n = 1,048 apiaries), nosema (n = 1,034), virus presence (n = 1,015), and brood disease symptoms and queen issues (n = 151).

So, what did they find? Were pesticides common in bee bread? Yes. Pesticide residues were found in 82% of bee bread samples and the likelihood of detecting pesticides was always high, though it varied from ….

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