A study originating in Switzerland recently added to an abundance of data that suggests that two insecticides, thiamethoxam and clothianidin, are related to honey bee decline. Thiamethoxam and clothianidin are members of an insecticide group called neonicotinoids. Partially banned in Europe, they are currently used by agricultural, commercial and residential consumers in Oregon.

Ongoing research, monitored by the Environmental Protection Agency (EPA) and the Oregon Department of Agriculture (ODA) and independent decisions by localities will determine the future use of these chemicals in our state.


A worldwide decline of honeybees was suggested as early as the winter of 2006, when beekeepers in the United States and Europe observed massive disappearances of the worker bee members of hives. Since then, the US Department of Agriculture has documented significant bee losses in this country, including data showing an 18% loss of colonies in the January-March quarter in 2015 and a 17% loss in the same quarter in 2016. More U.S. colonies (133,930) were lost in the first quarter of 2016 than the 92,250 lost in the same quarter in 2015.

A critical decline of pollinators such as honeybees would devastate worldwide food supplies. The Food and Agriculture Organization (FAO) of the United Nations estimates that out of some 100-crop species that provide 90% of food worldwide – 71 are bee-pollinated. The United States Department of Agriculture (USDA) estimates that pollinators are essential to about $15 billion of crops each year.

No scientist or entity has a definitive answer for the reason for bee decline, and it is usually attributed to a combination of factors and stressors. Possibilities include the varroa mite, a pest of honeybees, and other diseases, parasites and viruses. FAO adds habitat destruction, agricultural practices and poor bee nutrition to the list.

But insecticides have long been suspected as a prominent culprit since they, by definition – kill insects. The Swiss study incriminating neonicotinoids is only one of many to have singled out these chemicals.


Prior to the Swiss inquiry, research on neonicotinoids have focused on female bees. Those studies have shown that the chemicals can cause both lethal and sub-lethal effects on (non-reproductive) honeybee females and can impair the reproductive abilities of (fertile) female bumblebee queens.

The Swiss study, produced by an international team led by researchers at institutes of bee health and veterinary public health at the University of Bern and Agroscope in Switzerland – suggests that male honey bees, also called drones, are vulnerable to neonicotinoids as well.

fjk,,,Published in July 2016 in the journal, Proceedings of the Royal Society of London B, the report, titled, “Neonicotinoid insecticides can serve as inadvertent insect contraceptives,” showed that male bees with exposure to the pesticides had shorter life spans and produced fewer living sperm than males who did not.

The impact could be disastrous for a colony, since queen bees must be successfully inseminated with healthy sperm from multiple male drones if they are to lay the eggs that will ensure their survival.


Neonicotinoid insecticides, which include thiamethoxam and clothianidin are very similar to nicotine. They work systemically, taken in through leaves or roots or as a seed coating prior to planting and moving through a plant’s vascular system. They are registered for use in more than 100 countries and are produced by chemical corporations such as Bayer CropScience, Monsanto and Syngenta.

They are widely used in the United States, including on about 95% of corn and canola crops, as well as most cotton, sorghum, and sugar beet crops, and on about half of all soybean crops. They are used to kill insects on the great majority of vegetables and fruit crops including apples, berries, cherries, oranges, greens and tomatoes as well as potatoes, rice, nuts, and wine grapes.

Bees are exposed to neonicotinoids during or after foliar application (spray to leaves), or can ingest residues in nectar and pollen after the pesticide was applied as a seed treatment, or to the soil.

In 2013, in response to studies that suggested that neonicotiniods were linked to bee decline, Europe began to enforce the world’s first continent-wide suspension of pesticides by banning these pesticides. Evaluations of the effectiveness and consequences of this ban are still being made.


This year in Oregon, where the value of bees and other native pollinators is thought to be more than $500 million, 104 pesticide products containing clothianidin and thiamethoxam are approved for use in agriculture, landscaping and home gardens. Their purpose varies; one clothianidin pesticide, Arena, is used for white grub and leafminer control in turf grass, sod farms and ornamental plants. One thiamethoxam product, Avicta, acts as a fungicide and insecticide when applied to soybean seeds prior to planting. Another thiamethoxam, Maxide Dual Action Insect Killer, is used to control ants and leaf rollers on roses and evergreens.

Bee specialists such as entomologist Dr. Ramesh Sagili, Principal Investigator of the Honey Bee Lab at Oregon State, generally do not propose eliminating all insecticides to keep bee populations robust. “Any time you spray to kill an insect, you kill a bee,” he says, “that’s the tricky part. But farmers need the tools to produce food for us.”


The responsibility for determining which pesticides are used in Oregon falls on both the EPA and the ODA, though the EPA has the ultimate authority. After EPA tests a chemical, it writes the rules for use on its label, which is a legally binding document. Failure to follow label instructions is a federal offence. 

Rose Kachadoorin Oregon Dept of Agriculture

Rose Kachadoorin Oregon Dept of Agriculture

The Oregon Department of Agriculture works cooperatively with the EPA, says Rose Kachadoorian, ODA Pesticide Regulatory Leader. Oregon can never have less restrictive policies than the EPA requires, but it can, and does, have more restrictive ones.

“The EPA has a whole team of toxicologists,” she says, who continually evaluate scientific studies and determine national policy. “But if a state has a particular problem, such as shallow water, we can ask the pesticide maker for a prohibition specific to the state.”

Oregon can also tell manufacturers that they want to completely opt out of an EPA-approved product. Kachadoorian says. That it does so is evident on the Pesticide Information Center Online website created by Washington State University. According to the site, a number of neonicotinoid insecticides are registered and labeled for use in Washington, but not Oregon.

In response to Oregon mass kills, including seven incidents in 2013 and 2014 where nearly 100,000 bumblebees, representing hundreds of hives, were lost, the ODA banned the use of four neonicotinoids on linden trees, basswood trees or other Tilia species. Oregon’s refusal to allow the insecticide on lindens, Kachadoorian says, influenced the nation. After the label change in Oregon, the manufacturer elected to change its labels for every state. Now, no one can legally use the pesticide on linden trees anywhere in the U.S.

“We said we didn’t want to use it,” Kachadoorian says, “and we ended up impacting the use federally.”

According to ODA Director Katy Coba, the agency has a straightforward process for restricting products. “Regardless of the pesticide, if there is evidence that applicators have followed label directions, and there continue to be incidents of dead bees,” Coba says, “the agency would review whether additional restrictions need to be imposed.” She adds that ODA is working to develop an Oregon pollinator protection plan.


The EPA recently mandated that a bee image be placed on labels when product use might affect pollinators. Significantly, the agency is also in the midst of a new 2-year review of both clothianidin and thoamethoxam, performing risk assessments for these and other neonicotinoid pesticides. “As EPA completes risk assessments for neonicotinoids,” its website says, “the Agency will pursue risk mitigation, as appropriate.” It is conceivable that EPA will conclude from studies like the Swiss one that the insecticides should be further restricted or, like Europe, subject to a partial ban.

Some Oregon communities don’t want to wait. In 2013, the city of Eugene banned neonicotinoid pesticide use on city property by a unanimous city council vote. It was the first city in the nation to do so.

In 2015, Portland city council did the same.