Is Corn Earworm’s Evil Cousin Coming to Visit?

May 12, 2015 05:09 PM
Is Corn Earworm’s Evil Cousin Coming to Visit?

The arrival of this insect in North America could put 65% of U.S. agricultural output at risk.

Brace yourself for an ugly, expensive pest family reunion: Helicoverpa armigera, a cousin of the corn earworm (Helicoverpa zea), appears to be headed for North America.

According to researchers at the University of Minnesota, USDA’s APHIS, and universities in Australia and Brazil, H. armigera “has recently invaded South and Central America and appears to be spreading rapidly.”

It’s a troubling prospect. Also known as the Old World Bollworm, this insect "is considered to be one of the most significant pests around the world," according to Dan Borchert, an entomologist at USDA's APHIS who was interviewed by CBSMoneyWatch on the threat. 

The caterpillars of this Lepidopteran insect feed on a wide variety of commodity crops, including soybeans, maize (corn), wheat, sorghum, and cotton. It also eats flowers, tomatoes, lettuce and more.

Given that diverse appetite, the insect could feast on American fields. “Values for individual crops and for various scenarios indicate that 65% of total U.S. agricultural output is potentially exposed to H. armigera,” write the researchers, who published their analysis this spring. 

That could add up to some big losses for farmers.  If this pest did invade all the areas (and crops) where it could survive in the United States, “the annual value of crops that would be exposed to H. armigera totaled approximately $78 billion, with $843 million (worth of crops) growing in climates that are optimal for the pest,” according to researchers’ estimates.

Unfortunately, insecticides don’t appear to work very well on this pest, based on the experience of growers in Europe, Africa, and Asia. H. armigera “has repeatedly developed resistance to all chemical classes used to date, with some major disasters in both tropical and temperate regions,” they write.

They are also worried that H. armigera and H. zea could create a new hybridized insect that looks like one, but has the resistance to pesticides of the other. "The prospect of hybrids ... is one that would dramatically complicate control and/or eradication initiatives," according to the researchers.

What does seem to help? Choosing genetically modified seed that protects against lepidoptera.

In Australia, cotton plants with the Bacillus thuringiensis (Bt) trait are able to resist H. armigera; researchers think Bt corn and Bt soybeans may also thwart the hungry caterpillars.

Researchers also recommend using integrated pest management strategies (such as raising and releasing “susceptible moths” nearby) to keep the insect from becoming resistant to Bt plants.

“Overall, the overseas experiences suggest therefore that H. armigera is not an ‘Armageddon pest,’” they write, “but rather a problem that requires integrated management systems that are themselves managed to slow the development of pesticide resistance, and to respond to changing resistance patterns.”

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