A new study finds that reduced-risk pesticides are not less risky to beneficial insects.
A three-year study just completed in Michigan apple orchards showed that reduced-risk pesticides—which growers are now adopting—are more damaging to the functional ecology of the orchards than the products they are replacing.
Orchards using these reduced-risk pesticides have fewer beneficial organisms to help control pests, so growers will likely incur higher costs to control secondary pests, and use more, not fewer, spray applications, the study concludes. The reduced-risk orchards had fewer species of beneficial organisms and lower populations.
The study began in 2009 and involved 22 orchards. Dr. Mark Whalon’s laboratory, at Michigan State University, conducted the study, using funding from the Michigan Apple Committee.
It showed that the practice of using more insecticidal modes of action lowered the diversity of, as well as the number of, beneficial organisms, including pollinators. Growers are being encouraged to alternate among spray materials to reduce the development of resistant pests and also because the new reduced-risk materials are less broad spectrum. The shift in pesticides is coming about as a result of implementation of the Food Quality Protection Act of 1996.
“Because insecticides post-FQPA tend to be narrower in the spectrum of arthropods impacted, growers have to use a broader range of new modes of action to control a typical apple pest complex,” Whalon wrote in his final report. “Therefore, they are inadvertently reducing the diversity in their orchards.”
Some of the specific natural enemy changes they observed include:
- Green lacewings declined significantly in orchards using those insecticides defined by the U.S. Environmental Protection Agency as “reduced risk.” Numbers remained constant in the orchards sprayed with organophosphate insecticides, such as Guthion (azinphos-methyl).
- “Green lacewings as larvae tend to feed on soft-bodied insects like aphids,” Whalon wrote. “They look like little alligators as larvae and have beautiful, elaborate lace wings as adults. In fact, they can significantly impact pest populations.”
- Brown lacewing numbers increased, for reasons unknown. Brown lacewings are also effective predators.
- Asian ladybeetles declined in all tree fruit orchards sprayed with reduced-risk insecticides.
- Native ladybeetle species, particularly two-spotted ladybirds, increased in all the orchards. This might represent a “regional recovery,” Whalon said, “since their numbers declined after the Asian ladybeetle was introduced to counter the also-introduced soybean aphid.
- Aphid parasitoids greatly declined in reduced-risk orchards.
- Aphids, thrips, European red mites, and two-spotted spider mites noticeably increased in reduced-risk orchards.
Of the 22 orchards in the study, eight used organophosphate insecticides, eight used reduced-risk insecticides, and six used organic methods. The organophosphate orchards, where beneficial insects have gained resistance, were about equal to organic orchards in number and diversity of beneficials.
The study used yellow sticky traps to monitor for nine pest insects and 26 genera of beneficial insects and double that number of species, calling them “ecological indicators.”
After the Food Quality Protection Act was passed in 1996, Whalon became involved in evaluating effects of new actions being taken by the EPA. The phaseout of azinphos-methyl was of particular concern because both apple and tart cherry growers relied on it heavily for control of internal fruit-feeding insects. Tart cherry growers have yet to find ways, using reduced-risked insecticides, to achieve the total control of plum curculio and cherry fruit fly larvae required by the U.S. Food and Drug Administration.
While Whalon believes that azinphos-methyl can be dangerous to humans and to aquatic organisms, he is convinced that eliminating the chemical will have negative environmental effects as unintended consequences.
His recent study showed, in effect, that orchards under the reduced-risk regimen are more sterile of beneficial insects and will require more sprays for insect control, not fewer.
In a study of four orchards he did two years ago, he found that growers obtained “ecological returns” of $12.32 per tree when they used organophosphate insecticides compared with $6.89 using reduced-risk insecticides. Whalon has worked to quantify the value of “services rendered by beneficial organisms.” Just how valuable is it to have a green lacewing eat 600 aphids? Putting an economic value on that has been difficult.
If the apple industry had the functional ecology data that it now has when the EPA implemented the Food Quality Protection Act, it might have maintained azinphos-methyl’s registration with limitations, he said.
The Michigan Apple Committee has supported Whalon’s work to have real data available in the event that the well-being of growers is threatened by EPA or congressional actions.
These data will likely be even more critical for the Michigan apple industry as it lobbies for extension of the use of the organophosphate class of chemicals with government agencies as well as the public, Whalon said.