Two of the world's hungriest caterpillars have created a militant mega-pest capable of stripping billions of dollars a year from the food and fibre industries, Australian scientists have confirmed.

Key points: CSIRO scientists use mapped genomes to confirm existence of hybrid caterpillars in Brazil

CSIRO scientists use mapped genomes to confirm existence of hybrid caterpillars in Brazil The hybridised pest is likely to be highly resistant to pesticides

The hybridised pest is likely to be highly resistant to pesticides It poses no immediate threat to Australia but "global trade means global pests", researcher warns

The CSIRO researchers have evidence that the cotton bollworm and the corn earworm have hybridised to create a voracious caterpillar that's likely to be highly resistant to pesticides, according to their paper published in a US scientific journal.

"There's a risk we could end up with a caterpillar which incorporates the worst of both species," CSIRO senior research scientist Tom Walsh told the ABC.

The bollworm (Helicoverpa armigera) and earworm (Helicoverpa zea) feed on more than 200 types of crops including cotton, tomato, corn, soybeans and chickpeas.

The damage costs farmers in Australia and around the world $6 billion annually in lost production and control measures.

CSIRO researchers were part of an international team that last year completed an eight-year project mapping the genome of the two caterpillars.

Dr Tom Walsh works with cotton and its major pest, the cotton bollworm. ( CSIRO: Bill James )

At the time, the colonising bollworm — which is highly resistant to pesticides — was spreading rapidly through Brazil, and scientists feared it was cross-breeding with the resident earworm population.

CSIRO scientists have now used the mapped genomes to confirm the existence of multiple hybrid caterpillars in Brazil.

"Hybridisation between the two species increases the opportunity for novel, agriculturally problematic ecotypes to emerge and spread through the Americas and beyond," said Dr Walsh, who's one of the report's authors.

"They are very impressive little things. They can eat a wide range of hosts, seem to survive all our attempts to control them … and that really is my research interest: why isn't it dead when it ought to be?"

Although the mega-pest poses no immediate threat to Australia, we cannot afford to be complacent, he added.

"Globalisation and increased movement between countries and continents means movement of agricultural pests is becoming more common. Global trade means global pests," Dr Walsh said.

Estimated 65pc of US agricultural output could be at risk

Dr Walsh said the cotton bollworm appeared in Brazil around 2012 and has spread through most of South America and north into the Caribbean, including the US territory of Puerto Rico.

There have also been three detections in Florida, he said.

Researchers found more than 17,000 protein coding genes in the genomes of the bollworm and earworm. ( Supplied: CSIRO )

The report's lead author, Dr Craig Anderson, now with the University of Edinburgh, said the CSIRO research "has wide-ranging implications for the agricultural community across the Americas".

On top of the impact already felt in South America, an estimated 65 per cent of US agricultural output is at risk of being affected should the highly mobile cotton bollworm become established there, he said.

The bollworm is a particularly aggressive caterpillar and is not beyond eating its own kind.

"We had to separate the caterpillars in the lab, because otherwise we'd end up with just one big caterpillar," Dr Walsh said.

He said the research was an important step in enabling the global agricultural community to stay one step ahead in the international race to combat the mega-pest.

By understanding the gene flow between the two caterpillar species, there is now the possibility to use genetic tools to control the spread of undesirable traits as they spread, Dr Anderson added.

The research was published this week in the Proceedings of the National Academy of Sciences of the USA.