By Andrew Porterfield
A new study from the University of Minnesota has found that the selective insecticide sulfoxaflor is just as effective at controlling soybean aphids (Aphis glycines) as broad-spectrum insecticides, without causing significant harm to some beneficial predators of the aphid.
The new study by Anh Tran, Tavvs Alves, and Robert Koch, published in the Journal of Economic Entomology, shows that in the field, sulfoxaflor can control the soybean aphids as effectively as broader spectrum pesticides, and field and laboratory analyses showed that sulfoxaflor did not harm predators to soybean aphids nearly as much as did broad-spectrum insecticides.
The study provides more evidence that selective insecticides like sulfoxaflor could play a larger role in integrated pest management, which attempts to minimize the adverse impact on beneficial insects while effectively controlling pests.
The use of selective pesticides is especially important for the soybean crop in the United States, where 33.4 million hectares was harvested in 2014. One of the most important soybean pests in the north central United States is the soybean aphid, which can cause up to 40 percent losses in yield, and increased production costs by $25 to $50 per hectare since it invaded the region in 2000.
Last fall, the U.S. Environmental Protection Agency (EPA) issued a cancellation order for products containing sulfoxaflor after the Ninth Circuit Court of Appeals ruled that the EPA had not adequately determined the pesticide’s effect on honey bees. The EPA had approved the use of sulfoxaflor in May 2013. Currently, the Agency has proposed registration of sulfoxaflor with restrictions on application to pollinator-attractive crops, while it gathers more scientific information on the effects of sulfoxaflor on bees.
The Minnesota researchers conducted field experiments for two years, using visual whole-plant inspections and sweep-net sampling to determine soybean aphid populations and populations of their predators. They also performed laboratory experiments with three predators: the convergent lady beetle (Hippodamia convergens), the insidious flower bug (Orius insidiosus), and a green lacewing known as Chrysoperla rufilabris.
The researchers found that untreated soybean plants had six to seven times more aphids than plants treated with either of the insecticides, and that aphid populations did not differ between sulfoxaflor and broad-spectrum insecticides. The abundance of predators in the genus Orius and the family Coccinellidae was two to four times greater on soybean plants treated with sulfoxaflor compared to plants treated with broad-spectrum insecticides. However, the abundance of predators in the family Chrysopidae did not differ on plants treated with either insecticide or ones that were left untreated.
The sulfoxaflor effects were considered moderately harmful to O. insidiosus, harmless to slightly harmful to H. convergens and harmless to C. rufilabris, according to ratings by the International Organization for Biological Control.
Currently, the soybean aphid is managed by broad-spectrum insecticides like pyrethroids and organophosphates, which can have a detrimental impact on beneficial predators. In North America alone, the soybean aphid has more than 40 species of predators and parasitoids, making them important players in the management of aphid populations.
Sulfoxaflor remains under review as an alternative to broad-spectrum pesticides. Although it works similarly to neonicotinoid insecticides, its chemical structure is different, and it has a unique method for acting on nicotinic acetylcholine receptors, binding to those receptors instead of acetylcholine. It does not show cross-resistance with neonicotinoid insecticides.
In addition to soybean aphids, sulfoxaflor is effective against the sweetpotato whitefly (Bemisia tabaci), the greenhouse whitefly (Trialeurodes vaporariorum), the tarnished plant bug (Lygus lineolaris), the San Jose scale (Diaspidiotus perniciosus), and other pests. The insecticide also reduces populations of other aphids, such as the cotton, green peach and sugarcane aphid.
“This study provides the first evaluation of the compatibility of novel selective insecticide with natural enemies for management of A. glycines in soybean production,” the authors wrote. “Because management of A glycines in the north central United States currently relies primarily on foliar applications of only two modes of action (pyrethroid and organophosphate insecticides), there is risk of A. glycines developing insecticide resistance. The availability of an additional effective insecticide of a different mode of action would improve insecticide rotations for A. glycines management and help postpone the development of insecticide resistance.”
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Andrew Porterfield is a writer, editor and communications consultant for academic institutions, companies and non-profits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield on Twitter, or visit his Facebook page.