Soybean Tentiform Leafminer Emerges as New Pest

By Blake Jackson

The soybean tentiform leafminer, Macrosaccus morrisella (Fitch) (Lepidoptera: Gracillariidae), has recently emerged as a new pest of soybean (Glycine max (L.) Merrill) in the United States.

This North American microlepidopteran historically fed only on two legume species, American hogpeanut (Amphicarpaea bracteata) and slickseed fuzzybean (Strophostyles leiosperma).

Its first recorded occurrence on soybeans was in Québec, Canada, in 2016, with subsequent detections in Minnesota, South Dakota, North Dakota, Iowa, and Nebraska. In 2025, the pest was confirmed for the first time in Cooper County, Missouri.

Adult M. morrisella are small moths with a wingspan of 6-7 mm, displaying orange, white, and gray-black markings. Eggs are laid on the undersides of soybean leaves, and larvae progress through five instars. Early instars feed on sap, creating serpentine mines that expand into whitish blotch mines on the leaf underside.

Later instars consume leaf tissue, producing tentiform mines where pupation occurs. Under laboratory conditions, the full development from egg to adult takes about 25 days at 25°C.

Larval feeding reduces soybean leaf photosynthetic capacity by consuming tissue within the mines and causing mined areas to die. Damage is most noticeable on the mid- to lower canopy leaves. Scouting involves inspecting field edges near wooded areas for the characteristic tentiform mines on leaf undersides.

While specific economic thresholds for M. morrisella are not yet established, existing defoliation thresholds for other soybean pests 30% in vegetative stages and 20% in reproductive stages can be used as a guideline.

Management strategies are under development. Field trials suggest insecticides with translaminar activity can reduce larval populations and leaf damage. Additionally, some soybean cultivars appear less suitable for egg-laying or larval survival, indicating potential for breeding resistant varieties.

Continued research will refine scouting techniques, economic thresholds, and effective control measures to mitigate yield losses caused by this emerging pest.

Photo Credit: gettyimages-gilaxia