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Hybrid Swarm: A Threat to Food Security in South America

CABI Invasive Blog

By  Will Holland 

Australian scientists have published findings confirming the hybridisation of two of the world’s most invasive agro-pests into a more advanced ‘mega-pest’.

The cotton bollworm (Helicoverpa armigera) and the corn earworm (Helicoverpa zea) have been a major pest species, H. armigera widespread across Africa, Asia and Europe and H. zea having a more restricted rand of the Americas. Together they cause damage to over 100 crop species including corn, cotton, soybean and tomato, with management and control practices costing billions of dollars annually.

Researchers at the Commonwealth Scientific Industrial Research Organisation (CSIRO)have identified larval hybrids of the two-pest species in Brazil under the Biosecurity Risk Evaluation and Preparedness Programme run by Dr Paul De Barro. Initial hybrid population estimates are low, however, the combination of the two species into a novel hybrid with unlimited geographical boundaries is a major threat.

“A hybrid such as this could go completely undetected should it invade another country”, said Dr De Barro.

The surprise from the findings, and what is of particular concern, is that out of the studied specimens, every individual was a form of hybrid and none were the same. An example of this is one individual was found to be 51% earworm but contained pesticide resistant genes commonly found in the bollworm. This ‘hybrid swarm’ contains multiple versions of different hybrids within a single population, which poses a great risk to any form of prevention methods such as the use of pesticides as there was found to be varied levels of resistance within the population.

The implications of the potential spread of these hybrid moths is severe, as the agriculture industry in South America is already under pressure from invasive pests. Estimates suggest that over 65% of the USA’s agricultural output is also at risk from bollworm destruction, leading to fears that this estimate will be much greater following the potential introduction of these hybrids.

To see the original publication of these findings, please see the link below:


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