The screwworm is a terrifying insect. It’s a fly and, like all flies, breeds by laying maggot eggs on potential food sources. But instead of targeting rotting fruit or dead animals the screwworm fly goes for fresher prey. The females lay up to three hundred eggs on the exposed flesh of warm-blooded animals, targeting places such as open wounds or the navel. The eggs then hatch and hundreds of maggots burrow inward. It’s a major agricultural pest, can infect humans, and the infection (and subsequent secondary infections) can prove fatal.
But we have a clever way to eradicate it, one that turns the flies’ own biological drives against them. Instead of using pesticides or chemicals to try to eliminate the fly, scientists and governments have been using a method known as the sterile insect technique.
To put it in simple terms, scientists breed up a huge stock of male flies, sterilize them with radiation, and them release them into the wild. Male flies don’t attack animals and only live to impregnate the females. The females, presented with a sudden glut of males to choose from, are likely to end up picking one of our nulls. Lacking viable sperm, no eggs can be produced and no maggots can be laid. The best part? Female flies will only mate once in their lifetime. If she picks a null, that’s the end of her family line.
The United States pioneered this technique and successfully eradicated the screwworm from within its borders in the 1980’s. Since then other countries have followed suit. A sudden flare of screwworm infections occurred in Libya in 1988. Aircraft started air-dropping cardboard boxes of sterile males across the desert, releasing as many as 40 million nulls per week. Within a few years the outbreak was completely nullified.
There are some drawbacks to this plan. It can take longer to work than traditional pesticides and new batches of sterile males must be released periodically to really take effect. Sometimes nulls can be hard or expensive to breed. Nevertheless, it has no chemical residues and does not affect any species other than the target pest. It’s been lauded as an environmentally safe technique and other pests like the medfly and some local tsetse fly populations have also been effectively controlled with this method. Scientists are now targeting both Anopheles and Aedes mosquitoes (the vectors of dengue, yellow fever, and malaria) and other agricultural pests.