Two major crop pests, the cotton bollworm and corn earworm, have interbred in Brazil, creating hybrids resistant to multiple pesticides. This development poses risks to soya production and food security worldwide. Experts warn of potential yield losses and environmental impacts if the pests spread unchecked.
In Brazil, the cotton bollworm (Helicoverpa armigera) arrived in 2013, joining the native corn earworm (Helicoverpa zea), both known as megapests for their widespread damage to crops. These moths, which feed on a variety of plants including corn, tomatoes, and soya, have now hybridized, exchanging genes that confer resistance to pesticides.
Genetic analysis of nearly 1,000 moths collected over the past decade shows that one-third of H. armigera individuals carry Bt toxin resistance genes acquired from H. zea. This resistance originated in North America, where Bt maize was introduced in the 1990s, and has since spread southward. Conversely, nearly all H. zea in Brazil now possess pyrethroid resistance from H. armigera.
"It has the potential to be an enormous problem," says Chris Jiggins at the University of Cambridge. The pests' ability to travel long distances complicates control efforts, and hybrids could devastate soya crops, over 90% of which in Brazil are genetically modified Bt varieties producing a toxin from Bacillus thuringiensis.
Brazil's soya exports feed people and livestock globally, so reduced yields could drive up food prices and prompt more deforestation to expand farmland, increasing greenhouse gas emissions. "We’re just sort of blown away by how rapidly it’s happened," Jiggins adds.
Experts like Angela McGaughran at the University of Waikato highlight how global connectivity and climate change exacerbate such invasions. To counter resistance, farmers are advised to plant non-Bt crop refuges, though compliance is inconsistent. New multi-toxin Bt strains are emerging, but Bruce Tabashnik at the University of Arizona emphasizes preserving current protections through better management. While hybridization spreads resistance, intra-species evolution, as seen in China with H. armigera, remains the primary concern.
The findings, detailed in a bioRxiv preprint (DOI: 10.64898/2025.12.25.696198), underscore the need for vigilant pest monitoring worldwide.
