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DDT as a repellent

August 9th, 2007

I got an email today from Phillip Coticelli at Africa Fighting Malaria pointing to a study by Donald Roberts (PDF), showing that DDT has a repellent effect in addition to its toxicity. The key finding is that that three out of five DDT-resistant Aedes aegypti mosquitoes avoid huts sprayed with DDT. Roberts argues that this is a reason for preferring DDT to alternative pesticides such as dieldrin. A few points about this are worth making
* First, it’s good to see AFM acknowledging the fact of pesticide resistance, which primarily accounts for the abandonment of large-scale attempts to eradicate malaria-carrying mosquitoes with pesticides. The libel put out by people like Steven Milloy and AFM founder Roger Bate[1], in which it is suggested that the failure of the eradication program was due to a mythical ban on DDT imposed at the behest of environmentalists, who callously caused millions of deaths, depends critically on ignoring resistance.
* Second, although the study is new, the claim is not. Roberts has been arguing the importance of repellent and irritant effects for a long time. And while the reporting of this study suggests that these benefits are unique to DDT, other work by Roberts has found that permethrin and deltamethrin are just as effective in this respect.

How does this relate to the general debate over the use of hut spraying as a strategy to fight malaria?

First, it’s important to observe that, while DDT was never banned, it fell out of favor in the from the 1970s onwards as a result of the failure of the WHO’s attempt to eradicate malaria through spraying and of the adverse consequences of widespread use as an all-purpose pesticide, mainly in agriculture. The concerns which led to the abandonment of large-scale spraying weren’t as directly relevant to the alternative of indoor spraying, but past failures and the generally bad reputation of DDT didn’t help those advocating this strategy, notably including Roberts. In addition, the economic crises of this period made it difficult to organise the systematic programs required. International aid organizations concerned with malaria focused mainly on the use of bednets impregnated with insecticides, and on the development of improved treatments.

If indoor spraying with DDT had an undeservedly bad reputation in the late 20th century, the reverse is the case now. Thanks to the campaigns of AFM and others, it is taken for granted in conservative circles that DDT is a panacea, banned by evil environmentalists. As a result, whereas donors were once chary of funding DDT-based approaches, now poor countries are being pushed to use DDT whether or not it is appropriate.

It is, in some sense inevitable, that aid will come with strings attached, and that these strings will be pulled by domestic political forces in the donor countries. If the result is more money to fight malaria, it’s better to accept the associated constraints and take the money. Still, it would be good if we could move to policy driven by evidence, rather than by rich-country politics.

fn1. Acting on behalf of the tobacco industry which was fighting WHO attempts to restrict the spread of smoking, and needed to hit them on another front.

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  1. 2 tanners
    August 10th, 2007 at 11:08 | #1

    Most practitioners with a grain of sense know that with pesticides there is no magic bullet. Without commenting on DDT in particular, only a rotation of chemicals can be used to suppress population levels (not entire populations) of pests. The longer the rotation between individual chemicals the better, and the lower the dosage the better as well. Breeding resistance is madness.

    Specifically on DDT, I have heard World Wildlife Fund scientists argue that the outright banning of DDT was foolish, and encouraged the retention of far more dangerous and persistent chemicals. They also referred to the malaria argument in particular. (This was in the mid-90′s.)

    In 2001 the Stockholm convention on Persistent Organic Pollutants banned the production, use, import and export of DDT by signatories (about 190 countries, of whom 90-odd have submitted their implementation plans). this includes former large scale users and producers such as USA and PRC. Although you could argue it has never been banned, I think that for most intents and purposes, it has.

  2. observa
    August 13th, 2007 at 00:46 | #2

    “Still, it would be good if we could move to policy driven by evidence, rather than by rich-country politics.”
    I’m glad you think so John. Perhaps you’ll have to move your thinking a bit on say policies like Kyoto in the light of some serious revisions (hindcasting?) to NASA surface temp figures and perhaps the weather here
    http://www.news.com.au/story/0,10117,22221359-401,00.html?from=public_rss
    I guess the question we all need to ask ourselves now, is just how long should we wait until these computer models fine tune all that warming out of the system?

  3. BilB
    August 13th, 2007 at 05:10 | #3

    Dream on, Observa. No one is doubting that the polar ice is melting. Our Southern Australian weather is driven by sweeps of cold air that flow of the ice periodically. As the ice recedes and those sweeps become weaker it will not be good for rainfall in this part of the world. Not that anyone knows for sure what will happen. You appear to be from the “leave it to chance” brigade. To that I simply say that luck favours the prepared.

    On the DDT thing, when I was a kid in New Guinea there was a truck came around once a week with a fog maker on the back pumping out huge clouds of kerosene with DDT (to kill the Mosquitos). We called it the fluffy truck. It was a big event for us kids as we liked to run around in the fog bumping into each other and having great fun. Here I am fifty years later, still alive, but clearly damaged goods.

  4. observa
    August 13th, 2007 at 09:18 | #4

    BilB, if it were simply a leave it to chance choice, the choice might be somewhat easier. Now signing up to Kyoto has absolutely no effect on reducing GG emissions as we have already seen, but I am nervous about imposing another costly layer of ineffectual red tape on industry only too willing to offshore to non-Kyoto states. Whilst a noodle nation, where we all go from school to university for life and then on the age pension, sounds alright in theory, I’m just a little skeptical that it will work in practice. These reservations aside, I want to be totally convinced the climate computer models are spot on before we go charging ahead putting the third world’s scarce dinner into our petrol tanks.

  5. observa
    August 13th, 2007 at 09:49 | #5

    Bear in mind BilB, I’m a little older than some here and got used to the idea in the 70s we were heading for a new Ice Age. Then I had to gradually get my head around the idea, all that science at the time was wrong and we were really going to cook and just look at the 1998 record temp among other things. Now it appears that record temps occurred before WWII and the ‘weather’ has important cooling effects that need to be taken into account. Also the folk who discovered a Y2K glitch that caused the globe to cool a bit more are somewhat concerned about localised effects (like airconditioners) on temperature measuring stations. I must confess to being a confused layperson with respect to climate here, but I do understand what food affordability might mean for many. Presumably what housing affordability means for my countrymen, although it doesn’t affect me personally. Every new cloud has a silver lining I suppose. With all this GW, Kyoto and biofuels thingy, our unemployed homeless won’t be so cold at night and the world’s hungry won’t need so many calories anyway.

  6. observa
    August 13th, 2007 at 12:58 | #6

    Not quite so much certainty about now it seems-

    “Climate science is a very new science and we have only just begun to explore the uncertainties,” said David Stainforth of Oxford University in England who contributed research to the Royal Society.

    “We should expect the uncertainty to increase rather than decrease” in coming years as scientists work to understand the climate, he said.

    The Observa is not the only one who is a bit unsure of what’s going on with climate science these days
    http://www.news.com.au/adelaidenow/story/0,22606,22234851-5005962,00.html

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