Corn Rootworm Biology and Life Cycle

In the coming articles, I will cover the introduction Nurizma® Insecticide, a new soil insecticide from BASF for corn rootworm. But to understand the significance of another corn rootworm management tool, I would first like to set the stage by covering the biology of one of the most damaging insect pests in midwest corn production.

Species of Corn Rootworm:

There are a number of corn rootworm species that can damage corn. All go through an egg, larval, pupae, and adult stage. The larval stage damages corn roots and the adult stage beetle feeds on silk, both causing severe damage and yield loss to corn. Identified in their adult beetle stage, the three main species affecting US corn production are:

1. Northern corn rootworm (Diabrotica barberi). Northern corn rootworm beetles are tan when young, and then turn to a solid green.
2. Western corn rootworm (Diabrotica virgifera virgifera). Western corn rootworm beetles have black and yellow stripes.   Females have distinct stripes, while males have a more darkened spot or smudge.
3. Southern corn rootworm (Diabrotica undecimpunctata)  The southern corn rootworm beetle is yellow with twelve large black spots that are arranged in rows. It can be confused with the bean leaf beetle which is has a black triangle on it back and usually only four spots.

📸: BASF Contributing Writer/Featuring Northern corn rootworm (Diabrotica barberi) (Left) and Western corn rootworm (Diabrotica virgifera virgifera) (Right).

The southern corn rootworm by its name, cannot overwinter as eggs in cold climates, but adult beetles do migrate from the south causing some late summer damage to above ground foliage of numerous plants. They are commonly found in cucurbit crops as they are also known as the 12-spotted cucumber beetle.

The northern and western corn rootworm are major pests in midwest corn, as eggs can overwinter in cold climates, enabling larvae to damage corn roots. The adult beetles also emerge in time to damage silks.

Normal Life Cycle

Corn rootworm beetle eggs hatch around 700 GDU (June), then the larvae can only feed on corn roots. In the case of a corn soybean rotation where the eggs hatch in newly planted soybeans, the larvae cannot survive. Larvae go through three instars and then pupate in the soil. Adult beetles will emerge from the soil in later summer feeding on pollen and silks that can prevent pollination. The adults will lay eggs in corn fields utilizing cracks in the ground in late summer.

Variant Life Cycles:

There are variants of both northern and western corn rootworm that do not follow normal patterns and have found a way to flourish in a corn/soybean rotation. The evolution of these variants has caused a major increase in concern and shifts in corn rootworm management.

Northern corn rootworm variants lay eggs in corn, with some eggs having delayed hatching or extended diapause hatching two years later when corn is again in the field. Western variant adults will lay eggs in soybean with larvae emerging the next spring supplied with corn roots present in a corn/soybean rotation.

Damage to Corn:

Root damage from larvae feeding results in reduced root mass causing less ability to take up water and nutrients as well as poor standability causing goose necking and field or harvest loss. Damage is greatest from larvae root feeding in June, but adult beetles than can clip pollen in late July and early August can also cause serious yield loss. Root injury is rated on a 0-3 scale, where 0 is no feeding and 3.0 is three or more nodes pruned back to within 1.5 inches of the stalk.  Damage less than 1.0 is usually not of great economic concern but can be under dry conditions. Any damage over 1.0 will likely result in a yield loss with ratings above 2.0 resulting in severe yield loss.\\

📸: BASF Contributing Writer/Featuring roots pruned from Corn Rootworm (Left) and roots protected (Right).

📸: BASF Contributing Writer/Featuring goose-necked corn from Corn Rootworm.

General Rootworm Management Recommendations:

1. Rotate to another crop other than corn to breakup the life cycle.
2. Use Bt corn with Cry proteins or RNAi based trait to control larvae.
3. Use soil applied insecticides to control larvae.
4. Use foliar insecticides at R2 or R3 stage corn to control adult beetles before they lay eggs reducing pollen feeding and egg numbers.

Along with crop rotation as the number one tactic, growers have gone from reliance on seed and soil applied insecticides for larvae, or foliar applied insecticides for adult beetle control, then to Bt seed traits and now the RNAi technology as they became available. 

These management recommendations have worked well for the most part, but northern and western corn rootworm have not only shown the ability to adapt to crop rotation, but they also have developed resistance to some of the traditional insecticides as well as some of the Bt traits, and even the new RNAi technology.  

Because northern and western corn rootworm have found ways to evade control, growers are looking for alternative management methods. Look for an article on Nurizma® Insecticide, a new insecticide site of action control tool for corn rootworm.

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This content is being brought to you in partnership with Grow Smart® Live and contributing authors. BASF provides the information in this article as a service to its customers; however, the views expressed by guest writers are their own and do not necessarily reflect the views of BASF.