Soybean looper (Chrysodeixis includens) is an occasional pest of Alabama soybeans. Scouting and monitoring are critical because, in some years, soybean looper populations are much higher than in other years.

Soybean looper larvae look like most defoliating caterpillars, with a mostly light green color and a longitudinal white strip running parallel down both sides of the body. However, a few key features help distinguish soybean loopers from other defoliating caterpillars. Soybean loopers have two pairs of abdominal prolegs, while other defoliating caterpillars have three pairs (green cloverworm) or four pairs (velvetbean caterpillar) of prolegs. Soybean looper caterpillars also have a characteristic “looping” motion when they move, hence the name soybean looper.

Distribution & Life Cycle

Soybean loopers are found at some level in most soybean fields across Alabama. Moths migrate to Alabama during the growing season from more tropical climates. Upon arriving in Alabama, soybean loopers can have more than one generation within the growing season. Female moths lay eggs individually on the underside of leaves, and a single moth lays an average of 650 eggs during its life. Soybean looper eggs hatch about 3 days after being laid, and caterpillars develop through six instars (growth stages). Each instar lasts from 2 to 4 days, except for the sixth instar, which lasts 5 to 6 days. Thus, depending on environmental factors, the caterpillar life stage (when feeding occurs) lasts 2 to 3 weeks. At the end of the sixth instar, larvae move to the underside of the leaf to pupate in silken cocoons. The pupal stage lasts 7 to 9 days. Pupae are about ½ inch long and begin as light green but darkens as it matures. Soybean looper moths typically live for about 2 weeks. They are characterized as having a blackish-gray appearance and a wingspan of just under 1.5 inches. If observing the adults from above, the hindwings may appear lighter compared to the forewings, and usually, a white figure eight can be seen in the middle of the forewings. Adults are most active at night, which makes observing them difficult.

Pest Status

Soybean loopers are one of the most economically damaging caterpillar pests of Alabama soybeans. Although soybeans are susceptible to damage throughout the entire growing season, soybean looper infestations are more common later in the year (August through September). Soybean loopers damage soybean plants by feeding on the leaves, defoliating the plant. Signs of feeding are observed in the lower part of the plant canopy first, as this is where eggs are laid. As damage increases, upper portions of the canopy also begin to be defoliated. Typically, soybean loopers feed between the leaf margins, leaving leaves with a characteristic windowpane appearance. This feeding pattern is easily distinguishable from other defoliating caterpillar pests that consume the entire leaf. Defoliation in large amounts can significantly reduce yield by decreasing transpiration and photosynthetic activity. Soybeans are more susceptible to yield loss from defoliation during the reproductive stages because these stages are when the plant puts most of its energy into seed development.

Management Strategies

Due to their migratory nature, soybean loopers are a sporadic pest in Alabama soybeans. Scouting and monitoring are critical because in some years soybean looper populations are much higher than in other years. Since soybean loopers are a migratory and sporadic pest, automatic insecticides are not a viable management practice to control this pest. When scouting fields for soybean loopers, visual observations of defoliation and monitoring populations with sweep nets or drop cloths are recommended to determine if populations are reaching the economic threshold. Soybean looper can be a difficult insect to manage as most populations are resistant to pyrethroid insecticides. Further, intense insecticide selection pressure on populations as they migrate from southern latitudes can also complicate control. The most commonly used insecticides for soybean looper are chlorantraniliprole, methoxyfenozide, and Spinetoram. Because soybean looper is a migratory pest, control can be sporadic from year to year. Currently recommended economic thresholds and insecticides can be found in “Soybean: Insect, Disease, and Nematode Recommendations” (IPM-0413) on the Alabama Extension website at www.aces.edu.

Sawyer Hopkins, Graduate Student, and Scott H. Graham, Extension Specialist, Assistant Professor, Entomology and Plant Pathology, Auburn University

New March 2025, Pests of Alabama Soybeans: Soybean Looper, ANR-3139