Cerotoma

Cerotoma species are small to medium leaf beetles, generally 5–7 mm in length, with an oval to slightly elongated body shape. Adults typically display variable coloration, often yellowish-green to reddish with dark markings. Cerotoma trifurcata, the most studied species, commonly shows four black rectangular spots on the elytra and a distinctive triangular black spot at the junction of the thorax and abdomen. Antennae are thread-like and of moderate length. The genus can be distinguished from similar chrysomelids like Diabrotica (cucumber beetles) by body proportions and specific spot patterns, though species-level identification requires examination of genitalia or detailed color pattern analysis.

Agricultural systems and natural areas supporting leguminous host plants. Found in soybean fields, bean crops, and adjacent vegetation. Adults overwinter in leaf litter, field margins, and protected sites.

North America and the Neotropics. Records include the United States (particularly southern and midwestern states including Minnesota, Illinois, Louisiana, Mississippi, Arkansas, Tennessee), with southern Minnesota representing a documented northern limit for C. trifurcata populations. Neotropical distribution includes Central and South America.

Overwintering adults emerge in spring when temperatures warm, typically coinciding with emergence of host plants. Egg laying occurs in spring and early summer. New adults emerge in mid-summer, with potential for second generation in southern ranges. Adults seek overwintering sites in fall.

Larvae feed on roots and root nodules of leguminous plants. Adults feed on foliage, creating round holes in leaves, and may feed on pods. Documented hosts include Glycine max (soybean) and Phaseolus spp. (common bean).

• Glycine max - primary hostsoybean
• Phaseolus spp. - primary hostcommon bean
• leguminous crops - hostgeneral association

Overwintering adults emerge in spring and feed on young host plants. Females lay eggs in soil near host plant bases. Eggs hatch in approximately one week. Larvae pass through three instars, feeding on roots and nodules. Pupation occurs in soil. New adults emerge in mid-summer; second generation possible in favorable conditions. Adults migrate to overwintering sites in fall.

Adults are active during daylight hours. Strong flight capability allows dispersal between fields. Overwintering behavior involves aggregation in protected sites with leaf litter. Adults demonstrate preference for legume hosts and may move en masse into fields from overwintering sites.

Agricultural pest of legume crops. Larval root feeding damages nitrogen-fixing nodules, potentially reducing plant nitrogen availability. Adult defoliation can reduce photosynthetic capacity and pod feeding directly impacts yield. Serves as early-season pest in soybean production systems.

Significant economic pest of soybean and snap bean production. Bean leaf beetle (C. trifurcata) is a primary target of insecticide applications, including neonicotinoid seed treatments. Feeding damage can reduce yield; economic thresholds guide management decisions. The species has been demonstrated to show economic benefit from preventive insecticide treatments in high pest pressure regions of the southern United States.

• Diabrotica balteataSimilar size, shape, and habitat in soybean fields; distinguished by green or yellowish-green elytra with four lighter crosswise bands rather than black spots, and different head proportions
• Diabrotica undecimpunctata howardiOverlapping agricultural habitat and legume feeding; spotted cucumber beetle has different spot arrangement and more elongated body form

• agricultural pest
• soybean pest
• leaf beetle
• legume feeder
• Chrysomelidae
• neonicotinoid target
• early-season pest
• root feeder
• defoliator
• North America
• Neotropics

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Soybean Insects: Early-to-Late Season Pests (Emergence to R7) - AgriLife Extension Entomology
• Cerotoma-trifurcata - Entomology Today
• Treating Southern Soybeans with Neonicotinoids Yields Economic Benefits After All
• ID Challenge #16 | Beetles In The Bush
• Ecology and management of the bean leaf beetle Cerotoma trifurcata
• Ecology of the bean leaf beetle Cerotoma trifurcata (Forster): improving preventive and curative insect management
• Life Cycle of the Bean Leaf Beetle, Cerotoma trifurcata (Coleoptera: Chrysomelidae), in Southern Minnesota
• The literature of arthropods associated with soybeans : III, a bibliography of the bean leaf beetles, Cerotoma trifurcata (Forster) and C. ruficornis (Olivier) (Coleoptera: Chrysomelidae)
• Biology of Cerotoma arcuatus (Coleoptera: Chrysomelidae) and Field Validation of a Laboratory Model for Temperature Requirements
• Spatial and Temporal Distribution Patterns of the Bean Leaf Beetle, Cerotoma trifurcata (Forster) 1 , on Soybeans in Illinois 2