One of the cases discussed is the New World screwworm fly (Cochliomyia hominivorax), a parasitic insect in the Americas that primarily affects livestock but also harms wildlife and humans. Fresia, who began working on this species in 2003 during his master’s studies at PEDECIBA and later continued his PhD in Brazil, contributed to the article with his expertise in genomics and population biology. In Uruguay, IP Montevideo and INIA are leading a project that explores biotech strategies—including genome editing—to eradicate the fly.
Other cases examined in the article include the mosquito vector of malaria and three invasive rodent species that pose ecological threats in various regions around the world.
The article emerged from a workshop organized by the Hastings Center for Bioethics in New York and Arizona State University. It examines scenarios in which gene-editing technologies might be applied, arguing that in extremely rare and severe situations, targeted genetic modification could be ethically justified to address major threats to environmental, animal, or human health.
“Even the decision to eliminate parasites and disease vectors requires extremely compelling justification and confidence that eradication poses minimal risk to other species”, the authors state.
“It’s important that Science—given its editorial and scientific impact—provides space for this debate”, said Fresia, who is part of the Bioinformatics Unit (UBi) and the joint Pasteur-INIA Unit, and leads the screwworm fly project at IP Montevideo. “This clearly brings the discussion to a broad range of researchers and the public through science communicators. It encourages wider debate and will likely inform future decision-making processes given the complexity involved,” he added.
The Screwworm Fly in Focus
The New World screwworm fly (Cochliomyia hominivorax) is a parasite of warm-blooded animals, primarily affecting sheep and cattle, causing severe economic losses and animal suffering. Female flies lay eggs in the mucous membranes and wounds of animals, and the hatched larvae feed on live tissue, severely degrading the host’s health and often causing lethal bacterial infections.
The screwworm has already been eradicated from North America, parts of the Caribbean, and—until recently—Central America using the Sterile Insect Technique (SIT). This method involves mass-rearing flies and exposing their pupae to ionizing radiation to induce sterility. The sterilized insects (both males and females) are then released in target areas to mate with wild populations, reducing reproductive success and ultimately leading to population decline.
In South America, where the fly still persists, SIT has not been widely applied, largely due to its high cost. Uruguay is now moving forward with a program that uses SIT as a core tool for eradication. The article explains that SIT could become more cost-effective and efficient by using a genetically modified strain in which lab-reared female larvae do not reach maturity, allowing only male flies to be irradiated and released. These sterilized males would then mate with wild females, maximizing impact.
Another approach involves releasing non-sterile genetically modified males that carry a female-specific lethal gene (a method known as fsRIDL), which is passed on to offspring and eliminates wild females over time.
The authors argue that since most of the screwworm’s ecological interactions are shared with other species, and given the suffering it causes to animals and its negative effects on meat and dairy production (potentially affecting food security), its eradication may be ethically acceptable.
Mosquitoes and Rodents
The article also analyzes the case of Anopheles gambiae, the main vector of malaria, which kills over half a million people each year. Given malaria’s devastating historical impact and recent resurgence, the case for eradicating this mosquito may appear even stronger than that for the screwworm fly. However, the authors stop short of endorsing targeted extinction of the mosquito, arguing that the malaria parasite (Plasmodium) can be controlled through other strategies without eliminating the vector species.
In the case of three invasive rodent species—the house mouse (Mus musculus), the black rat (Rattus rattus), and the brown rat (Rattus norvegicus)—which threaten endemic bird species, particularly on islands, the authors acknowledge that local elimination using gene-editing tools might be viable. However, they emphasize that this would only be acceptable if there is no risk of global extinction of the species.
Implications and Public Participation
Gene-editing tools for species control are highly precise and targeted, unlike alternatives such as chemical pesticides or traps, which often affect non-target species.
Still, the decision to use such tools is complex and only ethically permissible if supported by strong moral arguments, inclusive decision-making processes, and thorough environmental risk assessments, the article stresses.
The authors raise important ethical questions, such as whether all species—be they insects, parasites, or mammals—hold equal intrinsic value, or if this value is shaped by human bias. They also note the double standard often applied to genetic modification compared to other human interventions in nature.
Adding another layer of complexity, they write: “Even if there were more clarity on the core moral issues, there are no simple, universally applicable criteria for deciding when the deliberate extinction of a species via gene editing is justified and when it is not. Both action and inaction have consequences and require justification.”
They also highlight the crucial role of local communities in decision-making processes. In particular, Indigenous communities and those directly affected by pest species should have a leading role, as they are the ones who will face the immediate impacts—positive or negative—of these interventions.
This is vital to avoid scenarios where the Global North—which often leads and funds these initiatives—imposes its solutions in the Global South, as seen in the case of malaria in Africa or the screwworm fly in South America.
“Local populations should have priority in decision-making. Their interests are clearly at stake, and they likely have specific knowledge of many of the potential social and ecological consequences of altering a shared environment,” the authors conclude.
