Cerotoma trifurcata

Distinguished from the banded cucumber beetle (Diabrotica balteata) by the arrangement of markings: bean leaf beetle has four spots or no pattern, while banded cucumber beetle has four transverse bands. The triangular spot at the elytral base is diagnostic for Cerotoma trifurcata. Separated from lady beetles (Coccinellidae) by body shape—bean leaf beetles are more elongate-oval with the head visible from above, whereas lady beetles are strongly convex with heads tucked under pronota. Color variation within the species can complicate identification; spotless forms occur.

Agricultural fields planted with soybean and other legumes; overwintering adults occupy woodlots, fence rows, and other sheltered sites with leaf litter and herbaceous debris. Favors areas with loose, well-drained soil suitable for larval development.

Eastern and central North America, from Canada (Manitoba, Ontario, Québec) through the eastern and midwestern United States. Particularly abundant in the Mississippi River Valley and southern soybean-growing regions. Documented in Arkansas, Louisiana, Mississippi, Tennessee, Illinois, Iowa, and Minnesota.

Adults emerge from overwintering sites when soil temperatures reach 10-15°C, typically April-May in northern regions, earlier in the south. Peak adult activity in soybean fields occurs during vegetative growth stages. Summer generation adults emerge mid-July to August. Adults enter reproductive diapause in September-October and migrate to overwintering sites. Partial second generations may occur in favorable southern conditions.

Adults feed on foliage, stems, and pods of leguminous plants, with soybean (Glycine max) as the primary host. Larvae feed on roots and root nodules of the same hosts, potentially reducing nitrogen fixation capacity. Documented hosts include soybean, snap bean, and other Phaseolus species.

• Glycine max - primary hostSoybean; adults feed on leaves and pods, larvae on roots and nodules
• Phaseolus vulgaris - hostCommon bean; adults and larvae utilize this host
• Bean Pod Mottle Virus - vectorTransmitting pathogen between soybean plants during feeding

Adults overwinter in diapause within woodlots and fence rows. Spring emergence triggered by temperature thresholds. Females deposit eggs singly or in small clusters in soil near host plant stems. Larvae pass through three instars over 3-4 weeks, feeding on roots and nodules. Pupation occurs in soil and lasts 1-2 weeks. Summer-generation adults emerge mid-summer, feed, and in autumn migrate to overwintering sites to enter reproductive diapause. Partial second generations documented in southern regions with extended growing seasons.

Adults exhibit migratory behavior between overwintering refugia and agricultural fields, moving in spring to colonize emerging soybeans and returning to sheltered sites in autumn. Overwintering aggregations form in protected locations with abundant plant debris. Adults are active feeders during daylight hours. Flight capability enables dispersal between fields and host patches.

Herbivorous pest of soybean with documented impacts on yield through defoliation, pod damage, and root feeding by larvae. Larval feeding on nitrogen-fixing nodules may indirectly affect plant nutrition. Serves as host for entomopathogenic fungi including Beauveria bassiana, which has been observed causing density-dependent mortality in overwintering populations. Acts as biological vector for Bean Pod Mottle Virus, contributing to plant disease epidemiology in agricultural systems.

Major economic pest of soybean in North America, with management requiring insecticide applications including neonicotinoid seed treatments. Research demonstrates economic benefits of preventive control in high-pest-pressure regions, particularly the southern United States. Virus transmission capability adds indirect damage beyond direct feeding injury. Subject of integrated pest management research focusing on scouting thresholds, resistant varieties, and biological control options.

• Diabrotica balteataSimilar size and host associations; distinguished by transverse yellow bands on elytra rather than spots, and lack of triangular basal spot
• Eriopis connexaBoth have spotted coloration and occur on soybean; distinguished by family-level characters—E. connexa is a lady beetle (Coccinellidae) with strongly convex body, hidden head, and predatory habit rather than herbivory

• agricultural pest
• soybean pest
• virus vector
• Chrysomelidae
• North America
• integrated pest management
• neonicotinoid
• Bean Pod Mottle Virus

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Soybean Insects: Early-to-Late Season Pests (Emergence to R7) - AgriLife Extension Entomology
• Treating Southern Soybeans with Neonicotinoids Yields Economic Benefits After All
• ID Challenge #16 | Beetles In The Bush
• Cerotoma-trifurcata - Entomology Today
• Ecology and management of the bean leaf beetle Cerotoma trifurcata
• Life Cycle of the Bean Leaf Beetle, Cerotoma trifurcata (Coleoptera: Chrysomelidae), in Southern Minnesota
• Ecology of the bean leaf beetle Cerotoma trifurcata (Forster): improving preventive and curative insect management
• The literature of arthropods associated with soybeans : III, a bibliography of the bean leaf beetles, Cerotoma trifurcata (Forster) and C. ruficornis (Olivier) (Coleoptera: Chrysomelidae)
• Spatial and Temporal Distribution Patterns of the Bean Leaf Beetle, Cerotoma trifurcata (Forster) 1 , on Soybeans in Illinois 2
• No-Choice Preference of Cerotoma trifurcata (Coleoptera: Chrysomelidae) to Potential Host Plants of Bean Pod Mottle Virus (Comoviridae) in Iowa
• Distribution of Bean Pod Mottle Virus in Arkansas Soybean as Related to the Bean Leaf Beetle, Cerotoma trifurcata , (Coleoptera: Chrysomelidae) Population 1
• Impact of Beauveria bassiana (Balsamo) Vuillemin on survival of overwintering Bean Leaf Beetles, Cerotoma trifurcata (Forster), (Coleoptera, Chrysomelidae)
• No-Choice Preference of <I>Cerotoma trifurcata</I> (Coleoptera: Chrysomelidae) to Potential Host Plants of Bean Pod Mottle Virus (<I>Comoviridae</I>) in Iowa