An Asian gypsy moth caterpillar sits on a leaf. The moth is a destructive invasive species recently found in Vancouver and Portland. State officials plan to spray for them this spring. (Washington Department of Agriculture)
The Port of Vancouver and parts of the Fruit Valley neighborhood are subject to an insecticide regimen to rid the area of a particularly destructive pest, but some residents are concerned about unintended consequences the program may have.
State officials are worried about European gypsy moths invading the Pacific Northwest, but they’re terrified of its Asian cousin. Asian gypsy moths were found in Oregon and Western Washington, including one at the Port of Vancouver, last summer. So agricultural officials in both states started planning their eradication.
In Clark County, 807 acres in and around the port have been treated twice. The first round of insecticide was applied by a helicopter in the early morning hours of April 17. The second was Monday. A third and final spray will be on May 1, weather permitting.
The European gypsy moth has already invaded the Eastern U.S. and, even though the female can’t fly, the species still moves around enough to defoliate about 700,000 acres of trees per year. The Asian variety hasn’t established itself in the U.S. yet, and officials want to keep it that way because those females have a flying range of 20 miles, and thus a population can spread even more quickly.
Decades of research
The agencies are spraying the bacterial insecticide bacillus thuringiensis kurstaki, or Btk, from the air at locations where the moths were found. The spray has been used for decades in organic farming, and research has shown no health impact to humans, fish, pets or bees — only caterpillars.
In the weeks since the first treatment, The Columbian received several emails and phone calls from citizens concerned about the quantity of spray used, the potential risks to human or animal health of spraying in residential areas, and the unintended consequences the treatment may have on native caterpillars and the animals that eat them.
According to Hector Castro, spokesman for the Washington Department of Agriculture, Btk has been widely applied aerially in residential and urban areas in a number of states over the years. Washington is applying half a gallon per acre, about half of the maximum rate allowed. That is the amount recommended for treating moth caterpillars.
“It has a long history of safe use around people, pets and other animals. The product has been reviewed by a WSDA toxicologist, by the EPA and the state Department of Health,” he said. “A Department of Health toxicologist has reviewed the full ingredient list and concluded it poses very low concern for health.”
Btk occurs naturally in soil. It kills caterpillars when it’s activated in their highly alkaline stomachs. It doesn’t harm vertebrates or other organisms that have acidic digestive systems.
The Oregon Health Department’s website says participants in a community survey done before and after an application of a Btk-based product reported an increase in symptoms such as irritated throat, stomach discomfort, itchy nose, dizziness and diarrhea after a spray. Still, it is considered by the Environmental Protection Agency, Health Canada and the World Health Organization as a least-toxic method of pest control.
WSDA partnered with the city of Vancouver to have two roadside signs put up. They were posted for the first spraying, but “a miscommunication” kept them from being posted before the April 25 treatment. Castro also said a Fruit Valley resident’s suggestion to put signs in public spaces such as city parks is a good one and WSDA would consider it for the future.
Although Btk is being sprayed to kill gypsy moth larvae, it will also kill native butterfly and moth populations that live in the area and are a food source to other animals.
The Xerces Society, an invertebrate-focused nonprofit based in Portland, isn’t opposed to the spraying but the group is not supporting it either.
“The reality is, we’re between a rock and a hard place,” said Aimee Code, pesticide program director of the Xerces Society. “It’s not that we want the Department of Agriculture to be applying pesticides but we recognize the dramatic concerns about damage the gypsy moth can cause.”
The group worries about native insect populations and local birds. Because the treatment areas are small, the society hopes the native species will return later on. Also, the spraying was timed to have as little overlap as possible with native caterpillars.
“We are concerned that a number of bird species will be feeding during the window. Their food source is going to be diminished,” Code said. “Your neighborhood doesn’t feel like a small space, but we’re hoping the effect we’re going to see is going to be short-term.”
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