Western Corn Rootworm

Adults are small yellow-green beetles; in the western corn rootworm the wing covers are marked with dark striping or shading, and males and females differ somewhat in pattern. Larvae are slender, white, worm-like grubs with a dark head and a dark plate on the last segment, found feeding on and within maize roots.

A characteristic symptom is "goosenecking", where plants with severely pruned roots lodge and then bend upward at the base as they try to right themselves. Digging and washing roots to look for feeding scars and tunnelling confirms larval activity.

There is generally one generation per year. Eggs are laid in the soil, typically in maize fields in summer, and overwinter there. Larvae hatch the following spring and must find maize roots to feed on, developing through several stages before pupating in the soil and emerging as adults in summer to feed, mate, and lay eggs.

Because eggs are usually laid in maize and larvae depend on maize roots, rotating to a non-host crop traditionally starved the larvae. In some regions, however, behavioural and developmental adaptations have reduced the effectiveness of rotation, underscoring the pest’s adaptability.

Larval root pruning reduces water and nutrient uptake and weakens anchorage, leading to lodging and goosenecking that hamper harvest and reduce yield. Adults feed on silks and leaves; heavy silk clipping during pollination can interfere with kernel set. Overall impact depends on larval density, soil conditions, and crop stage.

Maize is the key host, including sweetcorn. Larvae are highly dependent on maize roots, which is central to both the damage and the management logic for this pest.

Adult populations are monitored with sticky traps and visual counts through the summer to estimate egg-laying pressure and inform decisions for the following season. Root damage is assessed by digging, washing, and rating roots for pruning. Field history and regional resistance status are important context for planning.

Because the pest adapts to single tactics, durable management relies on diversifying and rotating approaches within an integrated pest management framework.

• Use crop rotation where local populations have not adapted to it
• Rotate and diversify management tools, including biotech traits where authorized, to slow resistance
• Monitor adults to estimate risk and guide next-season decisions
• Manage planting and agronomy to promote vigorous root systems that tolerate some feeding
• Coordinate resistance management across an area given the pest’s adaptability