Genetic modification of insects as pest control – Part 1

Vector borne diseases (VBDs) are generally pretty bad. Yellow fever, the disease which stopped the Panama canal dead in it’s tracks, makes your liver fail and turns you yellow… hence the name. Malaria is caused by a parasite which ruptures blood cells in unison. African trypanosomiasis makes you go to sleep and then die. Dengue fever lays you up in bed for six months in some of the worst agony imaginable. Hell, even veterinary VBDs are horrifying… outbreaks of rift valley fever usually present with random farm animal abortions.
In 2008, malaria alone killed 708,000 to over a million people, most of them young children in sub-Saharan Africa, and an estimated 190 to 311 million cases of malaria occurred worldwide, according to the CDC. Diseases like malaria, may actually work to keep poor regions poor. Control methods often do not reach the poorest people due to high cost… vector borne diseases tend to be diseases of poverty.
Check out this video made as a public service announcement in 1943 by Disney. Some of the control methods have changed, such as specific chemicals, but not that much.

So… what can be done to help save lives in regions with VBD problems? We can vaccinate, in those few cases where vaccines have been developed, and we can kill the vectors, but vector control efforts can be expensive. Education and awareness is great, too… let the locals know what the potential harm is and send them on search and destroy missions to remove insect breeding grounds.
But… and this is the cool part… we’ve got a new tool in our arsenal.
Genetically modified mosquitoes.

First, a history lesson for part 1, which will continue in part 2. We’ll get around to the whole mosquito thing in part 3.

Screw-worm larva.

A lot of techniques used in vector control actually originated in agriculture. Pesticides and degree-day systems that help predict growth of insects were both developed to help fight crop pests. Prior to the 1950s, one of the biggest pests of cattle in the US was a critter called Cochliomyia homnivorax, the New World Screw-worm. For cattle (and rarely… humans) this disease is even more horrifying than anything I’ve mentioned yet. This fly lays eggs in major or minor wounds of cattle, and the maggots proceeded to eat the animal from the outside in. Once one female lays her eggs, the smell of the infested wound would draw more and more females.
There were some rather fortunate quirks to the biology of this pest, though. It couldn’t overwinter in most areas of the US and the females only mated once while the males tended to be really ugly six-legged Casanovas. This meant that if we could eliminate them from their overwintering grounds, they wouldn’t spread over the US over the following year. They’d be gone.
Enter Raymond Bushland and Edward Knipling. They hypothesized that if we could sterilize male flies, each male would each prevent multiple females from laying eggs. If you kept this up, eventually the population would drop. If you kept it up a bit longer, eventually the sterile males would outnumber the fertile males.
This pretty little blue fly can mess up a cow pretty good. The number on the back is a sticker used to track the flies in recapture programs. We want to make sure they go out and get laid instead of hanging around their release sites.

So, this is what they did. They raised thousands upon thousands of screw-worms, bombarded them with radioactive cobalt which shredded the DNA in their quickly reproducing gametes, rendering them unable to bear children, and released them. The screw-worm was quickly eliminated and remains only in South America to this day, held at bay by release programs. Drs. Bushland and Knipling were the 1992 World Food Prize Laureates in recognition of their work.
There are some problems with this technique, though. Sometimes, the males which have gone through the radiation aren’t as competitive as the fertile males which results in the females favoring the wrong males from our point of view (you know… the one which matters) and sometimes the females mate multiple times which means that there’s only a decrease in reproductive output instead of elimination. There’s also the problem of working around radiation… we’re not talking about chernobyl grade material here, but whenever you can you’d ideally like to eliminate the risk to the people who work around these things.
Of course, science is by no means a rigid process. We try to refine our techniques whenever we can, and this will be the focus of Genetic modification of insects as pest control Part 2.

Joe Ballenger

Written by Joe Ballenger

Joe Ballenger is an agricultural scientist studying weed control at the University of Wyoming. He has a Masters degree in Entomology. He co-founded the successful Ask an Entomologist project!. In his spare time, he likes to cook and climb.

10 comments

  1. Great post, Joe! I didn’t know that the World Food Prize had entomologists on their list of laureates, but these guys definitely deserved it. You know the control efforts have been successful when most people haven’t even heard of the pest, right? Do you know if the screw-worm carries any diseases in addition to being totally horrible on its own?
    I love this video. The animations of the mosquito life stages are amazing. A lot of the things they show are still correct, except I’d replace Paris green with Bt tablets, and the diesel oil with something biodegradable. One thing that hasn’t changed is that the best method of mosquito control is removal of habitat, which means draining puddles and tipping over or filling in any man-made containers like cans or tires. I’d love to see this re-made with up-to-date information and distributed.

  2. I don’t think there were any diseases vectored by screw-worm per se, but females undoubtedly carried bad stuff through phoresy.
    I’ve always liked Disney stuff…they have a large series of videos like this one which I’ll post if I post on a relevant topic again.
    If I had time or drawing skills, I’d totally work on videos like this myself. Unfortunately, I’ve got neither of those things. 🙁

  3. I’ve been thinking more and more about how these videos could be updated. One thing I’d like to see this video updated with is with modes of action for pesticides. Let folks know what we think about how DEET works or how pyrethroids work as well as potential cross-resistance between pesticides and how that hampers control programs.
    It’s valuable information, and information in this format could go a long way in improving public perception of these types of endeavors…it’s not just GM food which has problems with public relations.

  4. Ok. doing something about Malaria and insects who fester in wounds is a noble goal. I just wondered if anyone thought of the Whole picture? What could happen to the birds, amphibians, etc.. etc.. who eat these GE insects? What about what could happen at the soil level? Isnt it true that all living things from the smallest microbe to the largest mammal have an ecological purpose??? Couldnt there be an unforseen, unexpected and even detrimental ripple effect?

  5. Isnt it true that all living things from the smallest microbe to the largest mammal have an ecological purpose???

    No. (getting at the whole ‘purpose’ thing here)

  6. Lisa brings up a good point, in that if one were to reduce or eliminate populations of insects, that could affect the predators that depend on them. Although the insects discussed in this post aren’t GE (genetically engineered) they are modified genetically through mutagenesis. It is important to note that control through pesticides or biological control or any other method that seeks to reduce the population of insects would have the same issue, and that is the ecosystem would be altered. We just had a journal club in my building yesterday, and we were talking about GE mosquitoes and this is one of the things I brought up. Genetic engineering was discussed as trying to control nature, when the method it would replace, pesticides, is also trying to control nature.
    Another thing I brought up are the geopolitics of this issue. Developing countries have the most trouble with Malaria, so they will be more likely to push for better solutions to their mosquito problems, however, wealthier nations might try to tell them that they cannot. I hope this will not be the case, but the discussion following the announcement the GE mosquito experiment on a Pacific island suggests otherwise.

  7. Yes there is a confusion between purpose and function here. Certainly, mosquitoes can function in an ecosystem, however, that is different from having a purpose in that ecosystem, as a purpose implies intention. There is one definition of function that is almost synonymous with purpose, and that would be a function that helps the organism (or in this case ecosystem) survive.

  8. Lisa…I would read part 2 and the upcoming part 3 because I actually address some of your points.
    Very briefly…
    1.) The critters here essentially feed just on mammals. It’s possible that deer populations could be affected, but I’ve not seen anything other than anecdotal evidence for this.
    2.) As for potential effects of things which eat animals, there are none of which I’m aware for radiation sterilized flies. There are also chemical methods of sterilizing insects using insect hormones as well as synthetic chemicals, but as far as I know radiation is used in all SIT programs.
    Now, in the RIDL programs discussed in parts two and three it’s unlikely there are any non-target effects because the protein needs to be at very high levels all the time. When mice have the gene put into them and express it as the flies do (which means it’s likely in much higher amounts than they could get simply eating insects containing the protein) are indistinguishable from the non-transformed mice.
    3.) As for the ecological effects of pest eradication. Your town pays a company to come through and spray for mosquitoes, so a technique like this could actually reduce the amount of pesticides sprayed depending on how many species need to be controlled.
    Secondly, this works on a level much more specific than pesticides. By definition, biological species only mate with their same species and no pesticide I’m aware of has a specificity that only knocks out one species whereas this technique selectively knocks out single species.
    Third, the species being targeted here are either species with a fairly narrow ecological breadth (screwworm), introduced (medfly) or live almost exclusively around humans (Aedes aegypti) so their absence isn’t really anything to be concerned about.

  9. As Joe says, reducing the populations of one insect species with special species-specific programs like SIT or RIDL won’t affect other species – which is very different from insecticides that will affect many species. In the case of the GE mosquitoes, any birds or amphibians or other animals that eat mosquitoes can still have their fill on other species of mosquitoes that don’t carry malaria that won’t be affected by this control method.

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