Massive Bee Kill Update

Yesterday, I posted about a massive bumblebee kill in Wilsonville, Oregon. At least 25,000 bumblebees were killed. The Oregon, Department of Agriculture (ODA) has tested bees and trees at the site and confirmed that bee deaths are directly due to exposure to the insecticide Dinetofuran. The trees had recently been treated to control aphids.

ODA and the Xerces Society (which advocates for protection of endangered species) are collaborating to cover the trees with netting to exclude bees. Hopefully, the netting will work like a bee veil for the trees. However, much of the damage is already done and many of the bumblebees in the immediate vicinity are dead.

Bumble bee hovers near bee balm

This massive bee kill is due to human negligence. Bees (including bumblebees) are pollen feeders. Bee foragers collect pollen from plants (including trees) and store it in their nest. The pollen is mixed with nectar to make “bee bread”, a nutritious food that the bees feed to their brood. It is well known that spraying trees that are in bloom will contaminate the pollen with insecticide that can kill bees. It is illegal to spray insecticides that are toxic to bees on trees that are in bloom. The Supplemental Label for Dinetofuran (Safari 20SG, For use on Ornamental Plants and Forests) clearly states, “For trees in forests that are pollinated by bees or other invertebrates, make applications post-bloom.” This rule has been violated.

How toxic is Dinetofuran to bees? Toxicity is reported as LD50, the dose of insecticide that will kill 50 percent of the bees tested. The EPA categorizes any insecticide with an LD50 of less than 2 ug per bee to be “highly toxic”. A ug is one millionth of a gram, smaller than even a tiny drop of water. Carbaryl, an insecticide feared by beekeepers as a killer of bees has a toxicity of 140 ng per bee or 140 billionths of a gram. Isawa and colleagues* measured bee toxicity of Dinotefuran at 75 ng per bee. Dinotefuran will kill 50 percent of the bees at less than half the amount as carbaryl; Dinotefuran is twice as toxic to bees. Independent measurements have found even greater toxicity for Dinotefuran. Dinotefuran is so toxic to bees that a bare whiff is lethal.

At issue for Dinotefuran and other insecticides of the neonicotinoid class is that their low toxicity to humans and low impact on vertebrates encourages their widespread use. However, the extreme toxicity to bees makes them unsuitable for use in a variety of situations. It is critical that those who are licensed to use pesticides follow the letter of the law and comply with all the rules. When the rules for use are ignored, bad outcomes (such as massive bee kills) can occur. If products cannot be used in a manner that protects the environment, additional restrictions on their use will follow. Many neonicotinoid insecticides are available for use by homeowners who may not read the instructions, fail to understand their implementation, or otherwise fail to follow direction. The word needs to hit the streets that all neonicotinoids are highly toxic to bees and should not be applied when and where bees are pollinating flowers.

*Crop Protection
Volume 23, Issue 5, May 2004, Pages 371–378