Hybrids Of Corn Earworm And “Old World” Bollworm Identified In Brazil

Corn Earworm. Photo: University of Illinois

Australian scientists have confirmed the hybridization of two of the world’s major pest species into what they say could be a new mega-pest.

Please note – this may get a bit confusing, owing to how the names are somewhat similar and also how the common and/or scientific names of insects tend to change over time.

The two pests are:

  • Helicoverpa armigera, which is found across the old world. It’s sometimes referred to, in fact, as the “old world bollworm” or the “cotton bollworm,” although it’s not the cotton bollworm found in the U.S.
  • Helicoverpa zea, which is from the new world. It’s more commonly known in the U.S. as the corn earworm or the cotton bollworm, among other things.

Armigera – the “old world bollworm” — was confirmed in Brazil in 2012 and 2013 but was probably present there as early as 2008, according to Dr. Tom Walsh, a senior research scientist with Australia’s CSIRO (Commonwealth Scientific and Industrial Research), which handles many of the duties assigned in the U.S. to USDA.

In Brazil, armigera settled into an area already population by Zea. As they say, nature took its course.

“These two species have been separated for about 1.5 million years and now are together in the new world and are hybridizing,” says Walsh.

Just to confuse things a bit more, both species were previously known as Heliothis armigera and Heliothis zea, Walsh adds.

Armigera  is widespread in Africa, Asia and Europe and causes damage to over 100 crops, including corn, cotton, tomato and soybean. It’s also a significant pest in Australia. It is extremely mobile and has developed resistance to pretty much every pesticides used against it.

The other pest, the corn earworm (aka cotton bollworm in the U.S) has developed limited resistance and host range compared to armigera.

Armigera was detected in south Florida on a limited basis in the summer of 2015.

Hybrids Could Be Hard To ID At Borders

Now, though, researchers have confirmed hybridization between the two species where they’ve come together in Brazil. CSIRO researchers offer clear evidence of the emergence of this crossing. Their findings appeared in the Proceedings of the National Academy of Sciences of the USA.

“A hybrid such as this could go completely undetected, should it invade another country,” says Dr. Paul De Barro, who heads CSIRO’s Biosecurity Risk Evaluation and Preparedness Program. “It is critical that we look beyond our own backyard to help fortify Australia’s defense and response to biosecurity threats.

“As Australia’s national science agency, we are constantly looking for new ways to protect the nation and technology like genome sequencing, is helping to tip the scales in our favor.”

While a combination of insecticides currently controls these pests well in Australia, it is important to study the pests themselves for sustainable long-term management world-wide, according to a CSIRO press release.

The scientists confirmed that among the group of caterpillars studied, every individual was a hybrid.

“No two hybrids were the same, suggesting a ‘hybrid swarm’ where multiple versions of different hybrids can be present within one population,” Walsh explains. “The bollworm, commonly found in Australia, attacks more crops and develops much more resistance to pesticides than the earworm.”

A concerning finding among the Brazilian hybrids was that one was 51% earworm but included a known resistance gene from the old world bollworm.

Lead author of the paper Dr. Craig Anderson, a former CSIRO scientist now based at The University of Edinburgh, believes the hybrid study has wide-ranging implications for the agricultural community across the Americas.

“On top of the impact already felt in South America, recent estimates that 65% of the USA’s agricultural output is at risk of being affected by the bollworm demonstrates that this work has the potential to instigate changes to research priorities that will have direct ramifications for the people of America, through the food on their tables and the clothes on their backs,” Anderson says.

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