25,000 Bumblebees and Counting

A devastating and very visible loss of native pollinators occurred (and is still ongoing) this week in Wilsonville, Oregon. Blooming linden trees at a Target store parking lot were treated with Safari, a systemic neonicotinoid insecticide manufactured by Valent Corporation containing the active ingredient dinotefuran. Applied as a soil drench or as a granules to the soil surrounding the tree, it is taken up by the roots and translocated to leaves, stems and flowers. The nectar and pollen are both highly toxic to bees. In this case, the trees were so toxic that the bees were killed on the spot. A Xerces Society biologist, Rich Hatfield, was on the scene and took photos of dead bumblebees hanging on the blossoms and the vast numbers of dead bees that had dropped to the pavement. A video of the kill has been posted by Portland’s local news station KGW.

Some bumblebees died immediately on the flowers that poisoned them.

The pavement under the treated trees was littered with dead bumblebees, as well as honey bees and ladybugs.

Bumblebees are social insects and live in small colonies in the spring and summer. Only young mated females overwinter as solitary bees to start the next year’s colony. Depending on the species, colonies contain 50 to several hundred bees. Nests about the size of a softball are built in the ground in old mole or gopher tunnels, in grass tussocks, or on the ground under a downed tree or rock. The overwintered queen starts the summer colony by laying a few eggs at a time, gathering nectar and pollen to feed the larvae. As the new bees hatch out, they are recruited to do the foraging, and the queen spends more time in the nest laying eggs. Towards the middle to end of summer, the queen lays the eggs that will become next year’s queens. When the young queens hatch out, they mate, and when the weather turns cool in the late summer and fall, they seek out a place for winter hibernation to start the cycle all over again.

This poisoning incident could not have occurred at a worse time for bumblebees, as the colonies to which these bees belonged have now lost their foraging force. The queens in the nests will not have the food and worker resources they need to produce new bumblebee queens for next year. At the current count of 25,000 dead bees and an average colony size of 75 bees, that is at least 330 colonies killed, and probably many more, since not all of the workers in a colony are out foraging. This is a devastating loss for native bees, for the crops that depend on them, and for the humans that depend on the crops for food.

The active ingredient in Safari, dinotefuran, is highly water soluble (39,800 mg/L), allowing it to be rapidly taken up by the plant through leaves, roots, and stems and expressed in the nectar, pollen and all other fluids in the plant tissue. This is the intended mode of action to kill target pests, but if it is used on blooming plants, it is deadly to pollinators that are attracted to the flowers. Dinotefuran is also quite persistent in the environment, and remains unchanged in the absence of microbial degradation. Even in the presence of microbes, the soil half-life was found to be 50-100 days, according to US EPA’s registration information for dinotefuran. Dinotefuran’s high water solubility and potential for ground and surface water contamination led the state of New York to deny the Safari and Venom product registrations in 2008, and dinotefuran is on California’s list of potential groundwater contaminants.

The bumblebee losses appear to be the result of an illegal application of the product to blooming plants. We’ll know more after the Oregon Department of Agriculture finishes its investigation. But even if the plants had not been blooming, it is not clear whether this product should ever be applied to plants that are attractive to pollinators at any time during the year. The  Safari label has the following ambiguous warning language:

Dinotefuran is a nitro-guanidine neonicotinoid insecticide. It is highly water soluble and very persistent in the environment and in plant tissue.

“This compound is highly toxic to honey bees. The persistence of residues and potential residual toxicity of dinotefuran in nectar and pollen suggest the possibility of chronic toxic risk to honey bee larvae and the eventual instability of the hive. This product is toxic to bees exposed to treatment for more than 38 hours following treatment. Do not apply this product to blooming, pollen shedding or nectar-producing parts of plants during this time period, unless the application is made in response to a public health emergency declared by appropriate state or federal authorities.”

The label notes that the product is “toxic to bees exposed to treatment for MORE THAN 38 hours following treatment,” indicating that 38 hours isn’t sufficient time to clear the toxin from the plant. The label goes on to say  “do not apply . . . during THIS time period.” But “this time period” is not defined. The average person would read the label and think that if they waited for 38 hours, the bees would be protected. And yet, the company literature indicates that only a single application per year is necessary to control insect pests. The treated plants remain toxic to insects at a level that will maintain pest control for at least a year. US EPA notes that the RT25 (the time at which any residual toxicity on foliage kills 25% of bees in a laboratory test) is 90 hours. A study of the metabolism of dinotefuran in spinach indicates that the parent compound has a half-life of 10 days; typically it takes about five half-lives (50 days) for more than 95% of a compound to degrade. The study also showed that degradation of dinotefuran in plants produces metabolites that are highly toxic to insects, but their half-lives were not measured.

It is time to reconsider the perceived “need” to kill all insects. The ornamental linden trees would be just fine with a little aphid damage. For the survival of our own species, we must not remove the fabric of the food web.