Genetically modified traits from commercial cotton have become established in wild cotton populations in Mexico, the crop’s centre of origin. They are now spreading on their own, years after GM cotton was first planted and far from where it is authorised. That is the finding of a new peer-reviewed study published in Environmental Pollution.
Researchers from the National Autonomous University of Mexico (UNAM) and the Institute of Ecology (INECOL) tested 72 wild cotton plants (Gossypium hirsutum) at two coastal dune sites on the Yucatán Peninsula. 47.2% of the plants carried at least one transgene.
The most common GM trait was cp4-epsps, which makes plants tolerant to glyphosate, the active ingredient in Roundup. It was found in 20.8% of plants. Insecticidal cry genes were found in 13.9%, and stacked combinations in 12.5%.
No commercial GM cotton cultivation has ever been authorised on the Yucatán Peninsula.
More than half of plants contaminated at one site
Contamination differed sharply between the two locations. At Chicxulub, a site with heavy urban and tourism influence, 74.3% of wild plants carried GM traits. At San Crisanto, a rural coastal community, the figure was 21.6%.
The authors say the results confirm earlier findings from the Ría Lagartos Biosphere Reserve. They argue that GM contamination in the region is not an isolated event.
A new GM combination no regulator has assessed
The researchers also found the insecticidal gene cry2Ab on its own in wild plants. In commercial cotton, cry2Ab is only sold as part of a stacked event, Monsanto’s MON-15985-7 × MON-88913-8, marketed as Roundup Ready Flex Bollgard II. In that product it always comes together with cry1Ac and the glyphosate-tolerance gene.
According to the authors, finding cry2Ab alone shows that stacked GM events are breaking apart and recombining in nature. They describe this as the first empirical evidence of stacked-event segregation in natural environments.
“The detection of cry2Ab in isolation is particularly significant because it represents a genomic combination that has never been subjected to regulatory evaluation,” the researchers wrote.
Wild plants are now spreading GM genes themselves
In Mexico, wild and cultivated cotton belong to the same species, so nothing stops them from interbreeding. The authors warn that contaminated wild plants have become “secondary sources of transgene dispersal”. They now cross-pollinate neighbouring wild plants whether or not GM cotton is grown nearby, which makes containment “practically irreversible.”
The study points to two routes that standard risk assessments overlook. The first is GM cottonseed sold as livestock feed, which is transported long distances without tracking; up to 3% of seeds can still germinate after passing through an animal’s gut. The second is birds, which collect cotton seeds as nesting material and carry them more than a kilometre.
The authors also note that the glyphosate-tolerance enzyme is linked to stress responses. It may be favoured by the salty soils of the coastal dunes where wild cotton grows, which could help explain why it was the most common GM trait found.
Knock-on effects for ants
The team also counted the ants living on each plant. In wild cotton, ants act as bodyguards: the plants feed them nectar, and the ants defend the plants against herbivores.
At both sites, plants with no transgenes had the most ants and plants carrying cry genes had the fewest. At Chicxulub the differences were statistically significant. Non-GM plants hosted significantly more ants than plants carrying the glyphosate-tolerance gene (p = 0.037) or cry genes (p = 0.003). The number of ant species showed a similar but non-significant trend.
The researchers note that their design was observational, so it cannot prove cause and effect. However, the pattern now holds across three separate localities. They warn that shifts in ant communities could favour invasive species such as Paratrechina longicornis over native defensive ants, with “cascading effects on other trophic levels” in coastal dune ecosystems.
Call for urgent regulatory overhaul
The authors conclude that current biosafety frameworks were never designed for what is now happening. Those frameworks test GM events for stability under controlled conditions and assume gene flow will be limited.
They warn that newer GM cotton varieties stack ever more traits; one already used in other countries expresses six transgenic proteins plus four marker genes. This, they say, could speed up the creation of new gene combinations in the wild, “whose long-term ecological and evolutionary consequences have yet to be empirically assessed.”
“Long-term monitoring across wild to domesticated complex of Gossypium hirsutum, coordinated with regulatory decision-making on new GM releases, is no longer a research recommendation, it is a conservation and regulatory imperative,” the authors wrote.
The study is dedicated to co-author Dr. Patricia Rojas, an ant taxonomist at INECOL, who died during the final stages of revision.
Study: Vázquez-Barrios, V., Butler, I.A.E., Rojas, P., Wegier, A. (2026). Transgene introgression into wild cotton populations generates long-term genetic and ecological effects in a center of origin. Environmental Pollution, 405, 128502. doi.org/10.1016/j.envpol.2026.128502 (Open access, CC BY 4.0)
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