COLUMBUS, Ohio – In Ohio, there are eight known insects that can devastate a soybean field in a single growing season: spider mites, stink bugs, grasshoppers, Mexican bean beetles, bean leaf beetles, soybean aphids, green clover worms and Japanese beetles.

There is another detrimental insect lurking, one that could singlehandedly destroy a farmer’s soybean field – the soybean gall midge. Fortunately for Ohio and Indiana growers, that pest is quite far away from their borders.

In late June 2018, entomologists in Iowa, Nebraska and South Dakota received reports of soybean fields with visible signs of dead or dying plants found to be associated with an infestation of cecidomyiid larvae at the base of the stem.

By 2020, damage had been reported in 114 counties in five states, and the culprit was determined to be a new species of gall midge in the family of Decidomyiidae. It was named Resseliella maxima, or the soybean gall midge. This pest, with its orange, stem-feeding maggots have spread into Minnesota and Missouri as well.

Soybean gall midge adults are delicate flies, ¼-inch long, with banded legs and mottled wings. They are rarely seen and live only 3-5 days. For infested fields, the highest plant loss is found at the edges of the field and decreasing in a gradient for plants further infield. The adults are only in the field for a short time and their average emergence period lasts about two weeks. It belongs to the same family as the Hessian fly and wheat midge. Researchers say the pest may have been in Nebraska since 2011.

“Everything we know today about the soybean gall midge is the result of the extremely persistent, well-connected and highly productive team of extension entomologists from the affected states,” said Justin McMechan, an entomologist who holds a doctorate in plant health from the University of Nebraska-Lincoln.

McMechan led that crop protection team and worked with growers, consultants and researchers to gather information about this important soybean pest.

“It’s a strange feeling to be working on an insect where nearly everything we do is a new discover,” McMechan said. “With such little information on soybean gall midge, we’re forced to share early results, which have fluctuated significantly between years.”

In June 2018, dead and dying soybean plants associated with soybean gall midge caused significant yield loss. Researchers discovered that three larval states of these cecidomyiids contribute to plant damage as internal feeding at the base of the stem caused plants to break easily and die. Mature larvae, with their bright orange color, drop from the base of the stem to the pupate in the soil. Three generations per year have been recorded. The last generation overwinters in silken cocoons, pupating in the spring.

Over the last two years, researchers have documented the extended emergence of adults from last year’s soybean fields in mid-June. The soybean gall midge, they discovered, has complete metamorphosis, which includes egg, larva, pupa and adult stages.

“The major challenge in trying to manage the pest is the lack of information about the basic biology and ecology of this new species,” McMechan said. “Creating an integrated approach to pest management requires a lot of data collection, patience and participation by growers and researchers. If the 2020 field season taught us anything, it’s that no single management tactic is likely to provide sufficient control against the soybean gall midge.”

The gall midge has reached central Iowa and the nearest infestation is 140 miles away from the Illinois border. Illinois had a surveying role in a large regional soybean gall midge sampling project called “Soybean Gall Midge: Surveying the North Central Regional, Adult Monitoring and Host Plant Resistance.”

Those in Indiana have already been forewarned about this pest’s movement. McMechan spoke at the Indiana Certified Crop Adviser Conference in 2020.

The pest’s movement eastward has some experts in Ohio on edge as well.

“Over the years, many Ohio farmers have adopted the Integrated Pest Management (IMP) approach when it comes to protecting their soybean crop,” said Kelley Tilmon, associate professor and state specialist for field crop entomology at The Ohio State University. “Farmers have implemented the practice of regularly field scouting and insect identification, which are key first steps in crop protection. They’re familiar with such pests as soybean aphids, stinkbugs, Japanese beetles and others, but scouting for unknown pests is not typically done by Ohio farmers. This new pest has never been seen before.

“We’re now aware that the soybean gall midge has been identified west of us, and thus far it has not been found east of the Mississippi River.”

Though the gall midge poses no immediate threat to farmers in Ohio, research funded by check-off dollars from the Ohio Soybean Council and the North Central Soybean Research Program is being conducted to learn more about this relatively new pest. “With funding from the Ohio Soybean Council, we’ve developed an information and identification postcard of the gall midge for farmers in Ohio,” Tilmon said.