Thursday, 11 February 2016

“Blame Zika mosquitoes on DDT ban” [updated]

Agribusiness professor Jacqueline Rowarth had a terrific piece in the most recent NBR, reminding readers that but for fact-free environmental bans on DDT back in the 60s on the back of Rachel Carson’s “lyrical but scientifically flawed” book Silent Spring – the book that captured a nation and helped kick-start the modern environmental movement – the Zika virus may have been a total non-starter.

The headline itself is plain enough:


The irony here is that Rowarth herself was inspired to study agricultural science in part because of Carson’s book. But she argues that the banning of DDT was wholly a “political move” on the back of the book, one “claimed as the first major victory for the environment movement,” but one with a tragic payoff – once with the failure to eradicate malaria that DDT had all-but promised (a failure that left millions to die), and now, again, with the rise and rise of the Zika-bearing mosquitoes.

Forty-four years from the banning of DDT, the lines of sad women in hospitals in Brazil, with their microcephalic babies in their arms or still in utero, have etched themselves into memory.
    People are wondering whether the scientifically-proven use of DDT could have prevented this tragedy. . . .

It’s certainly a fair question.

The headline writer at least has no doubts.

[Hat tip Julian D.]



  • “DDT is banned internationally by the Stockholm Convention on Persistent Organic Pollutants, an agreement ratified by more than 170 countries.
        “But an exception is allowed for malaria control -- a disease that still kills millions of people worldwide. Several countries, mostly in Africa, currently use DDT to combat malaria. …
        “Goldman said the pesticide is effective against the Anopheles mosquito, a night-biter that spreads malaria indoors while people are sleeping.
         “In many developing countries, DDT has proven effective when sprayed on the indoor walls of buildings.
        "’Basically the anopheles likes to rest on a wall surface between feedings and thus is poisoned by the DDT that is on the walls,’ Goldman said. . . .
        “But the mosquito that transmits Zika is not the anopheles but another genus known as the Aedes, which also transmits dengue and chikungunya viruses, according to Goldman.
        “Aedes mosquitos bite outdoors, during the day, she said. Spraying walls with DDT won't help.
        “The best way to deal with aedes is by controlling its breeding and using products such as the popular insect repellent DEET, Goldman said.”
    Zika virus: Is DDT an option? – CNN
  • “Although an official at the US Centers for Disease Control and Prevention has been quoted as saying that environmental concern about DDT ‘has to be reconsidered in the public health context,’ CDC spokesman Tom Skinner said the agency is ‘still working on vector control plans for Zika.’
        “It is ‘safe to say,’ Skinner added, that controlling Aedes ‘will involve lots of public education, eliminating breeding sites, larvicidal spraying, and spraying to kill adult mosquitoes in areas experiencing outbreaks.’
        “What sprays will be used has not been decided yet, but this ‘all of the above’ approach reflects the challenging biology of Aedes aegypti.
        “The most significant challenge is that Aedes evolved widespread resistance to DDT in the decades after the pesticide came into widespread use in the 1940s. The extent of that resistance has likely waned in the decades since use of the pesticide was curtailed, with more of the mosquito population evolving back to its pre-resistant, susceptible-to-DDT status. But that does not mean resistance has disappeared or that it will not come roaring back in response to DDT spraying.
        “’Once you have resistance, it generally stays in a population for a long time,’ Conlon said. ‘It’s not ephemeral like resistance to other pesticides, where a population reverts back to being susceptible.’”
    Zika outbreak revives calls for spraying with banned pesticide DDT – STAT


  1. I'm never in favour of banning things, but as far as bans go, banning DDT did simplify a large problem, namely the lack of property rights over wildlife, wilderness areas, rivers and oceans, and how to seek economic redress for damage caused within these areas and groups. DDT also has the potential to cause significant damage to human nervous systems, and with a build up in tissue from background sources, against redress for damage would be difficult.

    The ban hurried the shift from pesticides with horrendous half lives with the potential to cause significant damage to human health and wildlife if over used (and pesticides almost always are) to the organophosphates, the carbamates, then the pyrethroids and now the neonicotinoids. Each step more efficient and less toxic to wildlife and humans.

    Bayer et. al. produce 1000s of pesticides, many of which are capable of controlling mosquitos, mainly in the carbamate and pyrethroid classes.

    IMHO pining for DDT, especially given resistance issues which would have long ago rendered DDT ineffective if it had never been banned, is like pining for refrigerators which utilised CFCs, and became less effective at chilling food with each one produced.

    The problem is mainly an economic one rather than authoritarian one, again in my opinion.


    1. The thing is though, there was never a worldwide ban on DDT. Independent experts say DDT would not work against Zika because DDT was used too extensively in the affected countries in the past, and mosquitos are resistant.

      Ironically this is exactly what Rachel Carson warned about in Silent Spring. She cautioned against excessive use of DDT, rather than advocating an outright ban. Her critics aren't aware of this, because they never actually read the book; only articles written by other critics who didn't read it.

    2. Hi Ben,

      I've aware there never was a total worldwide ban on DDT, but there was and is an agricultural ban, which if it hadn't been in place would have likely rendered DDT completely ineffective if used en masse for decades.

      I deal with resistance a lot when treating my beehives for varroa. Resistance is not set in stone, where by as you treat with X tons, the target species consists of X% resistant individuals. In order to become resistant the species usually has to give some other form of fitness up, often reproductive fitness, so when the pesticide is removed (or replaced by another one that kills by targeting a different biological process) resistance to that specific pesticide will gradually decline as the resistant individuals are out bred by the more reproductively fit non-resistant individuals, but all this is dependent on how much was given up to become resistant. It why we cycle insecticides when treating, and due to resistance we also use biological controls, and organic chemicals as part of our varroa control plan. This should be the method of control of all pests and disease vectors, but it is more difficult and expensive in the short term.

      This issue isn't as simple as DDT versus mosquito, as a lathe when applied will strip away metal till there is nothing left, biological systems aren't close to working like that. There isn't only the resistance to pesticides, malaria itself is becoming resistant to our methods of treating it, the economic issues of; sanitation, swamp drainage, and access to treated bed nets are all required before a serious global elimination is possible, the lack of these is why the first attempt failed in 1969 (before DDT was banned).

      Which is why I'm quite heartened to see the OP has added a couple more articles, talking about these issues. I read through the original external links, and some of them were, in my opinion, eye rollingly simplistic pieces looking to blame environmentalists for millions of deaths without first making the case for it, not a simple task when talking about biological interactions, global issues around property rights, and tort law, to name a few.

      Us libertarians are supposed to be the ones dealing in the Truth, no matter how complicated or counterintuitive.


1. Comments are welcome and encouraged.
2. Comments are moderated. Gibberish, spam & off-topic grandstanding will be removed. Tu quoque will be moderated. Links to bogus news sites (and worse) will be deleted.
3. Read the post before you comment. Challenge facts, but don't simply ignore them.
4. Use a name. If it's important enough to say it, it's important enough to put a name to it.
5. Above all: Act with honour. Say what you mean, and mean what you say.