Secret Inert Ingredient in “Bee Safe” Pesticide Found to Kill Bumblebees

November 11, 2021 | Evidence is building that so-called “inert” ingredients in pesticide formulations are harming pollinators and undermining regulatory determinations that designate products as “bee safe.” According to a study published in Scientific Reports, the fungicide Amistar causes lethal and sublethal effects that can be primarily attributed not to its active ingredient azoxystrobin, but to alcohol ethoxylates, a proprietary, nondisclosed co-formulant, or inert (or other) ingredient intentionally added to a pesticide formulation— calling into question EPA’s little bee icon warning on product labels and the effectiveness of its regulatory review. In the study, all positive control bees died, and all negative control bees lived. None died from benzisothiazol, and only one died from naphthalene- sulfonic acid exposure. Fully formulated Amistar resulted in 23 percent mortality, while alcohol ethoxylates, and the mixture of benzisothiazol, naphthalenesulfonic acid, and alcohol ethoxylates resulted in death rates of 30 and 32 percent. Researchers find that bees that weigh more at the beginning of the study are more likely to survive. That is because alcohol ethoxylates are causing sublethal impacts that do not necessary kill every exposed bumblebee outright. [Straw, Edward and Brown, Mark. Co-formulant in a commercial fungicide product causes lethal and sublethal effects in bumble bees. Scientific Reports. 11(21653), 2021.]