Corn Earworm (Helicoverpa zea) Larvae Feeding on Cotton Plants Debra Ferguson/Design Pics Editorial/Universal Images Group (via Getty Images)
The cotton bollworm and corn earworm, recognized as “giant pests,” are currently wreaking havoc on farmers globally. Recent interbreeding incidents in Brazil have resulted in a hybrid that possesses resistance to various pesticides. If this trend continues unchecked, the hybrid strain may severely impact soybean and other crop yields, jeopardizing global food security.
“This can pose significant challenges,” notes Chris Jiggins from Cambridge University.
Many nations rely on Brazilian soybeans for both human and animal feed—“it essentially feeds the world,” Jiggins remarks.
In Brazil, over 90% of soybeans cultivated are genetically modified (GM) varieties containing built-in pesticides. The emergence of resistant pests could precipitate a decline in yields, leading to heightened food prices. Additionally, increased deforestation and greenhouse gas emissions may occur as farmers seek to clear more land for cultivation.
The corn earworm (Helicoverpa zea), a moth native to the Americas, features caterpillars that are highly destructive to a variety of crops, particularly corn. They also pose threats to tomatoes, potatoes, cucumbers, and eggplants.
Historically, H. zea has not been a significant issue for soybean farmers in Brazil, as soybeans are not their primary food source. However, the detection of the cotton bollworm (Helicoverpa armigera) in Brazil in 2013 marked a troubling development. This pest, a close relative of H. zea, has proven to be widely detrimental. Both moth species are categorized as “giant pests” due to their notorious destructiveness and resistance to control measures.
“The concerns are well-founded, given their significant impact,” Jiggins emphasizes. “Moths can travel substantial distances, complicating control efforts.”
H. armigera feeds on multiple plant types, while H. zea primarily reproduces in soybeans, leading to financial strains on Brazilian agriculture with costs totaling billions of dollars, according to Jiggins.
The introduction of Bt soybeans—genetically engineered to produce proteins derived from the soil bacterium Bacillus thuringiensis—has alleviated some challenges posed by these pests.
Initial belief held that hybridization between H. armigera and H. zea was implausible. However, genetic analyses from 2018 identified hybrids within the species. Recent genomic studies of around 1,000 moths collected over the past decade have revealed alarming trends.
Analysis indicates that one-third of H. armigera specimens now possess genes conferring resistance to Bt toxins, a concerning development since H. zea strains have evolved comparable resistances after their introduction in North America during the 1990s. This resistance, now spreading to South America, suggests a perilous progression as hybridization occurs. While hybrid H. armigera has not yet produced severe consequences, experts caution that as resistance continues to evolve, the situation may change rapidly.
Gene transfers between species are occurring, and H. zea in Brazil have gained resistance to pyrethroid insecticides. “The speed of this development is astounding,” notes Jiggins.
Angela McGaughran from the University of Waikato asserts that “as global interconnectedness and climate change enable species range expansion, the looming threat of these megapests could amplify on a worldwide scale.”
Farmers are advised to implement non-Bt crop rotations alongside Bt crops to mitigate the spread of resistant pests. However, adherence to these guidelines remains inconsistent across various countries.
Biotech companies are now researching multi-gene Bt strains—producing two, three, or even five different Bt proteins to combat resistance. However, Jiggins insists that the cost and duration of bringing such innovations to market underscore the necessity for sustainable resistance management, including reducing exposure to existing Bt crops.
While hybridization facilitates resistance, Tabashnik highlights that intra-species evolution remains the leading concern. In China, for instance, H. armigera has developed resistance to the original Bt toxin independently.
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Source: www.newscientist.com
