A study analysing data from the US Corn Belt, where GMO corn is intensively cultivated, reveals that pests have developed resistance to the transgenic crop.
GMO corn in the United States is generating a paradox. Widely used by farmers for its pest resistance and to boost yields, it has instead produced the opposite effect: pests have developed resistance and production is declining, resulting in economic losses for growers.
This is revealed by a study published in Science, conducted by a team of researchers from several universities in the United States, China and Canada, which analysed twelve years (2004–2016) of field data across ten states in the so-called Corn Belt, the agricultural region of the United States characterised by the intensive production of corn. The research focused on Bt corn (Bacillus thuringiensis), genetically modified to combat various pests including the corn rootworm (diabrotica).
The team collected data on pest pressure, crop yields and farming practices, comparing regions with continuous corn cultivation (western Corn Belt states: Illinois, Iowa, Minnesota, Nebraska, North Dakota, South Dakota and Wisconsin) with those practising crop rotation (eastern states: Indiana, Michigan and Ohio).
According to the findings, the intensive use of this genetically modified crop has actively encouraged the development of pest resistance, undermining the very effectiveness of GMO corn. Farmers planted more Bt corn than necessary, based on flawed perceptions of costs and benefits. This was most evident in the eastern states, where crop rotation had already helped reduce rootworm pressure.
The Science editors explain: "Pest resistance is one of the main traits introduced into genetically modified crops in order to reduce the need for chemical pesticides. However, when planted intensively, their effectiveness diminishes and the cost-benefit ratio shifts as pests develop resistance." Christian Krupke, one of the study's authors, compared Bt corn to a "finite resource" that is depleted with every use: "Every time you use it, you erode a bit of its susceptibility. So it's less likely to work as well the next time." As a comparison, it is the same phenomenon that occurs with the overuse of antibiotics, which leads to bacterial resistance.
GMO corn has generated a vicious cycle that led farmers to make intensive use of transgenic crops and ever-greater quantities of pesticides as the GMOs' effectiveness waned. The consequences have been economic losses tied to rising production costs and falling yields. Not to mention the environmental damage: beyond pesticide pollution, a study from some years ago found that the pest-control toxin in Bt corn also destroys insects that are beneficial to farmers, causing imbalances in the ecosystem.