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Hybridisation and the new frontier against spread of global pests

By Amy Edwards

April 6, 2018

caterpillar in cotton
Helicoverpa armigera Image: CSIRO

IT’S the stuff of science fiction. Hybridisation of two caterpillars in Brazil confirmed through extensive genomic testing by CSIRO researchers.

But it’s real and will enable the international agricultural community to stay ahead in the race to combat the megapest.

Helicoverpa armigera and Helicoverpa zea (commonly known as the cotton bollworm and corn earworm, respectively) are the world’s greatest caterpillar pests of broad-acre crops, causing in excess of US $5 billion in control costs and damage each year across Asia, Europe, Africa, America and Australia.

Researchers have used world-first genome mapping technology to confirm the bollworm has been spreading rapidly in Brazil and hybridising with the earworm.

The caterpillar is retaining the strongest characteristics of both species posing a real threat that the new and improved “superbug” could spread into the United States and cause widespread crop destruction.

Beware the hybrid swarm

The hybridisation research is outlined in a paper published in the Proceedings of the National Academy of Sciences of the USA (PNAS) journal this week.

Professor Gregory Sword, chair in cotton entomology at Texas A & M University, believes not only does the paper show clear evidence that hybridization is occurring, but the feared combinations of genes could result in new abilities as a pest.

“These findings bolster the idea that this situation should be considered an ‘invasive genome’ problem as much as an invasive species problem,” he says.

man in greenhouse wearing lab coat
CSIRO scientist Tom Walsh working with cotton and its major pest Helicoverpa armigera or cotton bollworm. Image: Bill James/CSIRO

CSIRO scientists have 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,” CSIRO scientist Dr Tom Walsh says.

“Globalisation and increased movement between countries and continents means movement of agricultural pests is becoming more common. Global trade means global pests.”

Forewarned is forearmed

To date, the hybridisation has not settled on a consistent genotype and scientists believe the time is now to act on global pest management and discuss the role of genomics in the future of pest management.

“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 favour,” Research Director leading CSIRO’s Biosecurity Risk Evaluation and Preparedness Program Dr Paul De Barro says.

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 domestically and world-wide.

caterpilar eating corn
The cotton bollworm and corn earworm cause US $5 billion in control costs and damage each year across Asia, Europe, Africa, America and Australia.

The bollworm, which is commonly found in Australia, attacks more crops and develops much more resistance to pesticides than its earworm counterpart.

A concerning finding among the Brazilian hybrids was that one was 51 per cent earworm but included a known resistance gene from the ballworm.

These hybrids may be undetectable by morphology or even conventional molecular tools. CSIRO’s whole genome sequencing is required.

Answer is in the detail

Last year, researchers identified more than 17,000 protein coding genes in the genomes of the cotton bollworm and corn earworm.

This level of detail makes it easier for scientists to predict the caterpillars’ weak spots, how they are responding to our attempts to control them and even help breed plants they will not want to eat.

The population of bollworm identified in South America is not the same as that found in Australia and suggests Australia was not the origin of the New World incursion.

Identifying pest origins is important for the development of resistance management strategies by enabling the inclusion of resistance profiles that reflect these countries of origin. Moreover, identifying incursion pathways will improve biosecurity protocols and risk analysis at biosecurity hotspots such as national ports.

Lead author of the latest Helicoverpa paper Dr Craig Anderson, a former CSIRO scientist now based at the University of Edinburgh, believes the hybrid study will have wide-ranging impacts down to everyday Americans.

“On top of the impact already felt in South America, recent estimates that 65 per cent of the USA’s agricultural output is at risk of being affected by H. armigera 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,” he says.

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