Soybean Gall Midge: Discovery of a Delicate and Destructive New Species
By Jody Green
When it comes to soybean, there is no shortage of pests. Soybean is a host plant grown throughout the Midwest and desired by aphids, beetles, grasshoppers, spider mites, and several caterpillars. Now let’s add a small midge with a big name and a reputation for destruction. Meet the soybean gall midge (Resseliella maxima). The name maxima means “greatest.”
The soybean gall midge is a newly identified pest of soybean. At this time, it is not found to exist in any other part of the world, but the discovery of its orange, stem-feeding maggots is a reality for many soybean growers where the borders meet along Nebraska, Iowa, South Dakota, and Minnesota, as well as Missouri.
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. The crop protection team, led by Justin McMechan, Ph.D., D.P.H at the University of Nebraska–Lincoln worked with growers, consultants, and researchers to gather information about this important soybean pest, which was published in February in the Journal of Integrated Pest Management. It is a story of curiosity, collaboration, and a strong network.
“It’s a strange feeling to be working on an insect where nearly everything we do is a new discovery,” says McMechan. “With such little information on soybean gall midge, we’re forced to share early results, which have fluctuated significantly between years.” In winter meetings, McMechan and others shared their deep appreciation for the soybean farmers who have graciously sacrificed their fields to gain critical data. These farmers have ridden the same roller coaster as the researchers in the efforts to learn more about it.
In June of 2018, dead and dying soybean plants associated with soybean gall midge caused significant yield loss, particularly at the field perimeter. The three larval stages of these cecidomyiids contribute to plant damage as internal feeding at the base of the stem causes plants to break easily and die. Mature larvae, known for 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 past two years, researchers have documented the extended emergence of adults from last year’s soybean fields in mid-June; those adults then move to the current year’s fields. Soybean gall midge adults are delicate flies, 1/4 inch long, with banded legs and mottled wings; they are rarely seen and live only for 3 to 5 days. Females oviposit in fissures near the base of soybean stems after the V2 growth stage. For infested fields, damage is spatially dependent, with the highest plant loss at the edges and decreasing in a gradient for plants further infield.
The major challenge in trying to manage the pest is the lack of information about the basic biology and ecology of this new species. Without historical data and knowledge, 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 soybean gall midge,” says McMechan. “We spent the last two years evaluating a wide range of cultural, genetic, and chemical control tactics, but unfortunately more time is needed to determine their stability and efficacy both alone and in combination.”
Extension entomologists from the University of Nebraska–Lincoln, Iowa State University, South Dakota State University, and the University of Minnesota communicate regularly to stakeholders via the Soybean Gall Midge Alert Network. They continue to monitor research sites and gather information across the geographic range in the Midwest. Stay tuned for more exciting discoveries from this team.
Journal of Integrated Pest Management
Jody Green, Ph.D., is an urban entomology extension educator at the University of Nebraska-Lincoln and a subject editor and communications editor for the Journal of Integrated Pest Management. Twitter: @JodyBugsMeUNL. Email: firstname.lastname@example.org.