Some maggots have gotten good press lately because of their helpful ability to clean out wounds by consuming dead tissue. Screwworms however; also known as Cochliomyia hominivorax, will never be welcomed in an operating room or anywhere else.
These are the creatures of nightmares. During part of their lives, they live and travel as flies, and lay their eggs in the wounds of warm-blooded animals. When the eggs hatch, the screwworm maggots feed on the living flesh of the infested animals.
Fortunately, we've learned how to control the screwworm and we might be able to apply what we've learned to controlling the insect vectors for human disease.
But there are some challenges.
My SciBlings at denialism blog paint a lovely image of the screwworm and its activities:
During the Civil War (since it was endemic to the South) the buggers would infest the wounds of soldiers and eat them alive - and they're called screw worms because attempts to remove them would make them burrow deeper in the tissue.
Fortunately, the screwworm was eliminated from the United States in 1966 through the use of sterile male insects. Current efforts focus on eliminating the screwworm from South America and parts of Africa, too. This has been a great benefit to both humans and farm animals.
[Of course, the sterile insect method for controlling screwworms and agricultural pests can't possibly be organic. It seems to me that organic farmers would frown on gamma irradiation. But that's another story.]
Naturally, people are interested in whether we can apply the same method that proved successful with screwworm to eliminating other kinds of nasty insects like mosquitoes and tsetse flies.
First, we make them sterile
To paraphrase Martin Enserink, from Science, two very powerful forces were used to accomplish this miracle: "sex and atomic energy."
The idea behind this method of control is that large numbers of sterile males are released into the environment. The females who mate with sterile males don't produce offspring. Over time, this method leads to smaller insect populations and can eliminate the insects or at least reduce the population.
That sounds pretty good.
It wasn't until I heard Dr. Zachary Adelman speak at the Fralin Biotechnology Conference that I realized how challenging this method could be when it's put into practice.
First, you need some form of radiation to sterilize the insects. Some places use gamma ray sources like cobalt-60 or cesium-130. But these radioactive materials could be misused if they were to fall into the wrong hands. Other people use X-rays to sterilize insects, but I'm not sure how well those methods have been worked out (except in Drosophila).
Next, you need to make sure that the insects you release are males. So, you need technicians to sort all those irradiated insects and dispose of the females.
Now, you have a bunch of sterile males. But, guess what? Surprise! Irradiated insects aren't exactly healthy and they don't compete well with their wild sex-crazed brothers.
So, the sterile, sickly, males need a little help to be successful at mating.
How is this accomplished?
Sheer numbers, baby! Sheer numbers!
Where do we get large numbers of sterile flies? Can we order them from Amazon?
Why, from fly factories, of course!
These are big operations and can be quite expensive. The Science article mentions that Ethiopia might spend $12 million building a single factory for raising testse fies.
There's one last challenge. Insects don't need passports to cross borders. Pest control with sterile insects works best on islands and places that can be geographically isolated.
In the US, there's a surveillance plant to watch out for screwworms that make it across the border. Countries with many borders have special problems dealing with flies that drop in for a visit.
It's method with promise, but it's not simple. Nor is it cheap.
Other articles in this series:
- part I. Summer time and the mosquitoes are biting