Hybridization Between Two Major Crop Pests Creates A "Mega-Pest" In Brazil

It is the caterpillars that cause the damage to the crops. CSIRO

Josh Davis 09 Apr 2018, 18:48

Even though the cotton bollworm and the corn earworm are some of the world’s most significant pests, you’ve probably never heard of them. These two species of moths cause hundreds of millions of dollars’ worth of damage every single year, and it turns out that they’re hybridizing to form what scientists are now calling a “mega-pest”.

While the two insect species are closely related, naturally they should be separated by the Atlantic Ocean. Unfortunately, as humans sailed the high seas, they broke this barrier and brought the two pests into contact with each other, with potentially worrying results, as shown in Proceedings of the National Academy of Sciences.

The corn earworm (Helicoverpa zea) is found in the Americas, where it is the second-most important economic pest species. Feeding not only on corn but also a range of other crops, it causes at least $100 million in damage every year, forcing farmers to shell out an estimated $250 million in pesticides to keep it at bay. Notoriously fast at breeding, it's a constant game of cat and mouse.

The moths cause significant damage on their own, so combined could be devastating. CSIRO

The cotton bollworm (Helicoverpa armigera) is a major pest in Africa and parts of Asia and Australia, and despite its name doesn’t restrict itself to just the cotton plant. It's also partial to feeding on tomatoes, maize, chickpea, alfalfa, and tobacco, causing significant economic damage as it eats its way through the crop. In Brazil, however, these two species have come together and started mating.

“A hybrid such as this could go completely undetected should it invade another country,” explains Dr Paul De Barro, from Australia’s Commonwealth Scientific and Industrial Research Organisations (CSIRO), who first picked up on this development, in a statement. “It is critical that we look beyond our own backyard to help fortify Australia’s defense and response to biosecurity threats.”

The researchers found that among every group of caterpillars they looked at in Brazil following the invasion of H. armigera, there were hybrids between the two species. Most of these were largely the cotton bollworm with some corn earworm genes scattered throughout, but one had stretches of genes that appear to show there had been previous hybridization.

Of most worry here, however, is that one hybrid contained a known resistance gene from the bollworm, and this could impact how farmers protect their crops against the corn earworm if it spreads into the population.

“On top of the impact already felt in South America, recent estimates that 65 percent 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,” warns lead author Dr Craig Anderson.

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