Mexican Bean Beetle in Soybean
Crop Damage: The Mexican bean beetle (Epilachna varivestis) occurs throughout Mexico, the eastern U.S., and the southern Great Plains. It is considered a sporadic pest in many Midwestern states and southeastern Canadian provinces. Larvae feed on the upper layer of soybean leaf tissue between the veins, giving leaves a skeletonized appearance. Adults feed on leaves and pods, and economic damage most often occurs when defoliation is severe.
Mexican bean beetle severe defoliation to soybeans.
Whitney Cranshaw, Colorado State University, Bugwood.org
Mexican bean beetle larva and skeletonized leaf.
Whitney Cranshaw, Colorado State University, Bugwood.org
Pest Description: Full-grown larvae are approximately 1/3 inch long, yellow-brown, and covered with six rows of yellow to dark brown branched spines along the back. Adults are ¼ inches long, oval-shaped, and range from dark orange to copper colored. A key characteristic of adults is the presence of 16 black spots arranged in three rows across the back.
Mexican bean beetle larva and adult.
Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
Scouting: Monitor fields regularly throughout the growing season, as both dry and wet conditions can reduce Mexican bean beetle populations. Randomly select plants throughout the field and estimate whole-plant defoliation as well as the percentage of plants with pod damage. Use the Crop Protection Network’s Insect Defoliation Tool to accurately assess defoliation levels.
Management: Treat fields when defoliation reaches 30% during vegetative stages or 20% during reproductive stages. Consider treatment earlier if adults are actively feeding on pods. Insecticide applications may be necessary under outbreak conditions.
A Mexican bean beetle larva and adult on a leaf. The yellow larva is spiky and adult is light orange and spotted. Image by Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.
Soybean canopy with skeletonized leaves caused by Mexican bean beetle. Image by Whitney Cranshaw, Colorado State University, Bugwood.org.
An orange colored and spiky Mexican bean beetle larva and skeletonized leaf tissue. Image by Whitney Cranshaw, Colorado State University, Bugwood.org.
Gallery images courtesy Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org and Whitney Cranshaw, Colorado State University, Bugwood.org.
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