Permission to release
Recently, Florida officials granted permission for hundreds of millions of genetically engineered mosquitoes to be released locally. While at first this sounds like an experiment from Jurassic Park, the aim of the release is to reduce local mosquito numbers, specifically those species which transmit diseases such as dengue.
The blame for transferring diseases lies with only female mosquitoes, who bite humans and other animals for blood to support growing eggs. They have been described as the most dangerous animal in the world, carrying diseases that account for up to a million deaths per year worldwide. The disease burden is exacerbated by the fact that some currently have no existing cure, such as dengue.
Controlling local populations of species has historical precedents dating back to the 1950s in America. Rather than mosquitoes, screwworms were in the crosshairs, which can bore through live flesh and, thus, were destroying livestock. Scientists employed the use of X-rays to sterilise blowflies, the adult form of screwworms, and then released them. Upon release, the sterile males mates with local females resulting in sterile offspring, effectively lowering the screwworm population. Consecutive releases over the following two decades brought the population down and brought it back under control.
The sterile insect technique
The more modern technique being employed in Florida is called the sterile insect technique, and substitutes irradiation for the more specific and cheaper method of genetic modification through gene insertion. The company involved, Oxitec, inserts a lethal gene into male mosquito embryos, which are then reared to adulthood and released to mate with local populations. The gene kills off female offspring before they reach mature biting age, effectively targeting disease transmission.
While genetic engineering is a new method of disease control in Florida, Oxitec are actively involved in several countries, including Brazil and the Cayman islands. The British company have built a factory in Brazil and rear the modified insects on site, upon which they sell them to towns and municipalities. The prospective success of a Florida operation will build on previous achievements of the company, such as a reduction of mosquito numbers by 96% on the Cayman islands.
The company also face considerable adversity, however, from both environmental activists and other experts in biology and global health. One criticism is that the method could create hybrid mosquitoes resistant to insecticides, a concern heightened by the current crisis of resistant insects. Another issue is the lack of a separate, independent impact assessment of the methods, highlighting the lack of external regulation of Oxitec. Further, one could argue that while humans pose a risk to a great many species, it would be morally wrong to drastically lower the numbers of a single species that is only a danger to humans. Many critics point out that targeting mosquitoes specifically will only result in opening up a niche which will be filled by another insect. As it is impossible to predict which insect would replace mosquitoes, it could potentially be a similar or even worse disease vector, worsening the public health situation.
Another aspect to remember is that, while they pose a significant disease burden, mosquitoes have several positive influences on ecosystems. For one, they are an important food source for many animals, including birds, bats and fish, so removing them from local environments could have huge consequences further along the food chain. Also, mosquitoes are key pollinators, and help make rainforests largely uninhabitable to humans, thus contributing to limiting our environmental impact.
So, while Florida prepares for a new and modern method of disease control, opinions are split between previous successes of the technique and strong criticisms and concerns. Several alternative methods of mosquito population control have been put forward, including more effective repellents and making mosquitoes resistant to the disease-causing parasites. In reality, the future of population control is likely to be a combination of genetic engineering and other novel methods such as these, as differing public and expert opinions make it very difficult for one technique to monopolise.