Iowa Farmer Today

A Western bean cutworm feeds on an ear of corn. The increased planting of biotech hybrids might be one factor that allowed the pest to spread across the Cornbelt, according to an Iowa State University entomologist.
Photo courtesy Pioneer Hi-Bred

JOHNSTON --- The Western bean cutworm, which moved across Iowa from 2000 to 2004, has in the past year moved into the eastern Cornbelt and south into Missouri.

Researchers are working to understand why the insect, which has been in Nebraska since 1936, is moving.

The cutworm moved into Western Iowa in the 1970s, notes Marlin Rice, Iowa State University Extension entomologist. However, its population dropped at that time.

He says one change since then has been the introduction of biotech corn, which suppresses the corn earworm. Fewer insecticides also are being applied.

The earworm is a very aggressive insect, says Rice.

It will eat other insects and other corn earworms. Therefore, there only will be one earworm per ear of corn.

Rice says the cutworm is not aggressive — it does not attack other cutworms. So, one ear can have multiple cutworms.

Some biotech hybrids have a protein to control the earworm and other insects, such as the rootworm and European corn borer, he explains. However, that same trait, the Cry1AB gene, does not control the cutworm.

Rice says the cutworm was previously a minor pest. In Iowa, one larva per ear can mean between 4-11 percent yield loss, he adds.

In Nebraska, one larva per ear at dent stage reduced yields by 3.7 bushels per acre. Multiple larvae per ear produced losses up to 50-60 percent.

The cutworm also can allow an access point for molds to enter and affect corn quality.

Overall, Rice says damage from insects has increased. Because of that, he wanted to study the interaction among corn earworms, cutworms and biotech hybrids.

He put various sizes and combinations of the two insects in the same controlled environment.

“It is like putting two kids in the backseat of a car,” Rice notes.

Then he put three diets — artificial, non-biotech silks and a biotech hybrid with Cry1AB gene silks — in the controlled environment.

He found the cutworms had a survival rate of about zero to 20 percent in the artificial and non-biotech silks diets. However, almost all the cutworms survived on the biotech-silk diet.

That is about the same as his control, when Rice put two cutworms in the same controlled environments and they died.

He also noticed the earworms would kill cutworms. This did not happen when the cutworms were larger than the earworms.

However, Rice says earworms generally grow faster than cutworms.

He concludes biotech corn could be “one piece of the puzzle” why the Western bean cutworm has become more of a damaging pest, which has spread across the Cornbelt.

Other cultural practices also could be influencing the cutworm’s population growth.

Companies are either working on or promoting their products to control the cutworm.

Rice would not guess which insect would replace the cutworm if traits were used to control it. He says it goes back to the old saying, “Nature abhors a vacuum.”