Control Strategies for the Soybean Tentiform Leafminer
US soybean farmers should be on the alert. The soybean tentiform leafminer, known officially as Macrosaccus morrisella (Fitch) (Lepidoptera: Gracillariidae), has recently become an emerging pest to soybeans, according to the University of Missouri.
Historically, this North American microlepidopteran fed only on two native legumes: American hogpeanut (Amphicarpaea bracteata) and slickseed fuzzybean (Strophostyles leiosperma).
Its first documented attack on soybean occurred in Québec, Canada, in 2016. Since then, the pest has been detected in Minnesota, South Dakota, North Dakota, Iowa, and Nebraska. In 2025, it was confirmed for the first time in Cooper County, Missouri, signaling its continued spread.
Adult moths are small, with a wingspan of 6–7 mm, displaying a mix of orange, white, and gray-black patterns. Females lay eggs on the undersides of soybean leaves, and larvae develop through five instars.
Early instars feed on leaf sap, creating serpentine mines that later expand into whitish blotches. Older larvae consume leaf tissue, forming tentiform mines where pupation occurs. Under controlled conditions at 25°C, development from egg to adult is roughly 25 days.
Larval feeding reduces photosynthetic capacity, primarily affecting mid- to lower-canopy leaves. Scouting should focus on field edges near wooded areas, where the characteristic tentiform mines are visible.
While no specific economic thresholds for M. morrisella exist, general soybean defoliation thresholds 30% during vegetative stages and 20% during reproductive stages can serve as interim guidance.
Management approaches are in development. Field studies indicate that insecticides with translaminar activity can suppress larval populations and damage.
Additionally, some soybean cultivars may be less attractive for egg-laying or less suitable for larval survival, suggesting potential for resistance breeding.
Ongoing research aims to refine scouting protocols, establish economic thresholds, and develop effective control strategies to limit yield losses from this new soybean pest.
Photo Credit: istock-oticki