beekeepers to use in colonies to combat Varroa. While varroacides were the most prevalent chemicals detected, with few exceptions they had little impact on pesticide risk in those samples. However, this was not in all cases, and beekeepers must continue to be mindful of the amount and frequency of varroacides they apply to their colonies. Herbicides: Herbicides were found in about a quarter of the samples, and while they have increased in number and frequency during the study period, overall herbicide concentrations found in samples have not changed. However, a small number of samples in this study (8) had herbicide concentrations above 1,000 ppb for either atrazine, fluridone, propachlor or metolachlor. Fungicides: The Fungicides were the second most commonly detected group of pesticides following varroacides. And the numbers are going up — the number of fungicides detected has increased over time from 4-10, and often more than one is found in a single sample. In fact, 9.4% of the samples that tested positive for fungicides contained 5 or more different fungicides — and nearly 1/3 of these were California samples. Insecticides: Twelve insecticides were found the main contributors to the pesticide concentrations detected in the 52 “high risk” samples. These chemicals are therefore of greatest concern with regard to current colony health risks (Figure 2 lists these insecticides). Neonicotinoids were only detected in 2% of the samples. However, when they were present, they represented a large proportion of the overall pesticide risk to the colonies in which they were found. While it is encouraging that insecticide prevalence has declined over time, this study shows insecticides continue to occur in honey bee colonies, and are usually the pesticide responsible for the increased risk in “high risk” samples. How Great is the Risk? Agricultural producers face a multitude of harmful pests and diseases that they must manage throughout the year to keep crops healthy while also trying to maximize production. This often requires the use of one or more pesticides that, even when used appropriately, may pose some degree of risk to
How Common and How Many? 120 unique pesticides were detected from the 2011–2017 samples, with 81.9% of all samples containing at least one pesticide. The maximum number of pesticides detected in a single sample was 21, but the average was 2.78 pesticides detected per sample (Figure 1). While overall pesticide prevalence remained about the same across survey years, prevalence of the major pesticide classes — fungicides, herbicides and insecticides — did change, with insecticide prevalence decreasing, and both fungicides and herbicides increasing over time. What, Where and How Much? Sample pesticide concentration is measured in parts per billion (ppb) and is calculated by summing up the concentration of all the pesticides found in a sample. Average sample concentration was 600.3 ppb (± 82.0) with relatively few samples showing values above 1,000 ppb (indicating elevated risk). Pesticide concentrations did vary across states, with some states showing averages above 1,000 ppb: California = 1,110.0 ± 228.7; Delaware = 1,228.1 ± 700.2; Indiana = 1,306.8 ± 999.7; New Jersey = 2,941.7 ± 1,475.7; New York = 1,239.3 ± 373.1; and West Virginia = 1,146.1 ± 753.8). Varroacides: It is not surprising that the most commonly detected pesticides were the varroacides DMPF (the breakdown product of Amitraz; 45.38% prevalence) and thymol (20.63%), products currently recommended for
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