The good mosquito versus the bad
Florida will embark on a gigantic biological experiment in 2021. The outcomes, whatever they are, will influence global public health and environmental policy. The danger is, this is on the kind of scale where negative impacts could be irreversible.
Starting 2021, around 750 million genetically modified (GM) Aedes Aegypti mosquitoes will be released in batches into the Florida Keys. These insects are all male, which means they won’t bite humans. Only pregnant female mosquitoes bite — the female of the species is genuinely more deadly than the male.
Therefore, these GM males will not transmit Zika, dengue, yellow fever or any of the other diseases carried by this mosquito. All the infections come via the exchange of fluids when pregnant female mosquitoes bite.
The killer app: These males have been modified to carry a specific protein in their genetic code. That protein is supposed to be lethal to female eggs. The plan, this swarm of GM mosquitoes will impregnate normal Aedes Aegypti females. In the next generation, only male eggs produced by those matings will be viable and those males will also carry the protein.
Over generations, the gender ratios will change and, as fewer female mosquitoes are born, the Aegypti population will be drastically reduced. The life cycle is between 2-4 weeks, so this skewing of gender ratios should be effective pretty fast.
A drop in the population will lead to a drop in infections. The US Environmental Protection Agency has approved the trial. Small pilot trials have been previously successful in Brazil with 95 per cent drops in population. Another trial involving the Asian Tiger mosquito on a couple of Chinese islands has seen similar positive results.
This is a potential alternative to pesticides and it has the endorsement of the World Health Organization. The mosquitoes have been created by a company called Oxitec. It’s claimed the Aedes Aegypti has been adapting to pesticide strains since the brief life-cycle triggers faster mutations.
There are multi-fold potential dangers. One is dangerous effects on the food chain. Mosquitoes are eaten at the egg and larval stage and as adults by fish, frogs, toads, lizards, turtles, etc. There will first be a surge in population as those 750 million males are released. Then, if this experiment works, there will be a sharp drop in population.
This may create a feast followed by a famine. If there’s a drop in populations of frogs, lizards, etc, that would affect snakes, turtles, alligators and other species that eat these smaller animals. We could, therefore, have perturbations across the food chain in one of the most fragile and wonderful ecosystems in the world.
The other danger comes from “robust hybridisation”. In that Brazilian study, 450,000 mosquitoes were released each week for 27 months into Jacobina in Bahia Province. That’s about 48 million male mosquitoes. The actual populations would have been quite a bit less, as it will be in Florida, because the release consists of placing male eggs in ideal conditions in the wild and there is natural attrition.
However, while the Jacobina pilot resulted in 95 per cent of local populations being wiped out, a study in Nature (https://www.nature.com/articles/s41598019-49660-6) says that “genetic sampling from the target population at 6 months, 12 months, and 27–30 months after releases commenced provides clear evidence that portions of the transgenic strain genome have been incorporated into the target population. Evidently, rare viable hybrid offspring between the release strain, and the natural Jacobina population are sufficiently robust to be able to reproduce in nature.”
The study says it’s unclear what the effect will be in the long-term, or in terms of disease transmission. The implication though is that lethality is not complete with this genetic modification. Some hybrids do survive, and these may be able to produce female eggs that perpetrate the hybrid strain.
Given the much larger scale of this Florida trial, that hybrid population could be significant in size. This experiment and its results will be debated by policymakers, seeking public health solutions with minimal environmental impact.