Research Highlights

A North American Moth is Expanding its Turf to Soybeans

By Carol Brown

A tiny, native North American moth has recently discovered the goodness of soybeans — but it isn’t good news for farmers. 

Macrosaccus morrisella, normally found in wooded areas, was discovered in soybean fields in Quebec, Canada, in 2016. University of Minnesota entomologist Robert Koch was alerted to this pest by his Canadian colleagues and proceeded to find it in southern Minnesota soybean fields in 2021 and in eastern South Dakota in 2022. He has been tracking it ever since. 

“This pest has always been here and the larvae are known to feed in forested areas on two native plants in the same family as soybean,” explains Koch. “But this moth seems to have undergone a host range expansion and is now feeding on soybeans.”

The pest’s common name is the soybean tentiform leafminer — bestowed by Koch and approved in 2023 by the Entomological Society of America. He is studying its life cycle, its host plant preferences, and insecticide efficacy through a project supported by the Minnesota Soybean Research and Promotion Council and the Minnesota Rapid Agricultural Response Fund with the University of Minnesota.

“The soybean tentiform leafminer is a tiny moth that lays its eggs on the underside of soybean leaves and they hatch directly into the leaf,” explains Koch. “The larva (caterpillar) lives inside the soybean leaves and as it feeds, it tunnels, or hollows out the leaf tissue, leaving what we call a mine. Their mining affects the soybeans similar to a defoliator, as they eat and kill the leaf tissue.”

The mines can be seen on the underside of the soybean leaf, and as the larvae get older, the mines become visible on the upper surface as well, says Koch. The moth and the caterpillars are so small that one larva doesn’t cause much damage, but when they dine in the same spot, they can kill larger tissue areas. Once they pupate and become adult moths, they mate and the process starts over again. Part of Koch’s research will track how many generations occur over one soybean growing season. 

Even though the moth is native to North America, there is only minimal information about it and almost no research has been done regarding its relationship to soybeans.

“Similar to the soybean gall midge, we’re kind of starting from ground zero to understand this insect,” says Koch. “We’ve been successful at establishing a colony of soybean tentiform leafminers in the lab and we’ll be doing a lot of lab studies on them.”

He’s hitting the ground running with studies to get ahead of its possible detrimental impact. Thanks to the two funding entities, he and his research team will be looking at a number of objectives:

• Finding out when the soybean tentiform leafminer begins to attack soybeans,
• Learning how many generations there can be in a growing season,
• Locating them in the fields (edges vs. interior) and in the state,
• Determining if it prefers certain soybean varieties and if there are soybean varieties resistant to it,
• Identifying which insecticides are effective in killing adults and larvae, and
• Exploring parasitic wasps that attack the leafminer.

Koch created a fact sheet for farmers and other entomologists to help with scouting and identification. He will update the information as his research reveals more about this pest. He encourages Minnesota farmers to contact him if they suspect the soybean tentiform leafminer could be in their soybean fields. 

Other Resources

Soybean Tentiform Leafminer in Minnesota Soybean – University of Minnesota Extension fact sheet

First Reports of Macrosaccus morrisella Feeding on Soybean, Glycine max – Journal article, Entomological Society of America

Published: Oct 2, 2023