There are two major species of corn rootworm (CRW) in the U.S. cornbelt: Western corn rootworm (WCRW) and Northern corn rootworm (NCRW). This article covers how to tell them apart and what management strategies to consider for each.
How To Identify Western and Northern Corn Rootworm Adult Beetles
Here are three ways to tell Western and Northern CRW beetles apart. IMPORTANT: Color alone is not always reliable as both species can vary in shade and intensity of yellow/green coloring.
1. Wing Cover (Elytra) Color and Pattern
Western: Black stripes on yellow/green background
NOTE: Stripes may sometimes merge, but the pattern will still be visible
Northern: Solid green/yellow color, no stripes
2. Size and Shape
Western: Slightly larger and more robust
Northern: Generally smaller and more slender
NOTE: Western females are noticeably larger than Northern females
3. Antennae Length
Western: Antennae are long, about 2/3 length of body
Northern: Antennae are shorter, about 1/2 length of body
NOTE: Both species of CRW have segmented antennae, but the length difference is noticeable
Western CRW: Slater, IA 2025
Cultural Control Notes
Crop rotation is traditionally the most effective cultural control. However you should consider extended rotations of non-host crops where pressure is high.
CRW pressure: Slater, IA 2025
Western Corn Rootworm Management
In some areas (mainly Illinois and Indiana), WCRW has developed a “soybean variant” that lays eggs in soybean fields, which then emerge the following year if corn is planted.
Watch-Outs:
- Rotate corn with non-host crops besides soybeans if the soybean variant is present
Northern Corn Rootworm Management
Certain areas have seen extended diapause in NCRW. This is a genetic adaptation that allows a significant percentage of eggs to remain dormant in the soil for multiple years before hatching. This gives NCRW more opportunities to reestablish itself in a year following soybeans and makes it more challenging to control.
Watch-Outs:
- Consider 3+ year crop rotations where extended diapause is common
- Monitor beetle populations in non-corn years
- Most effective when extended rotation matches local diapause patterns
Universal Management Tips
The following guidance applies to both varieties of corn rootworm.
Soil-Applied Insecticides
- Use a targeted application method at planting for maximum root coverage
- Prioritize fields with a history of damage and continuous-corn acres
- Consider economic thresholds from beetle counts
- May need to apply in second-year corn due to extended diapause
Bt Corn Hybrids
- Use pyramided traits when available
- Implement proper refuge requirements
- Monitor for effectiveness and resistance development
- Rotate different Bt proteins across seasons