August 20, 2007
"Big Mosquito" Indeed
Posted by scott at August 20, 2007 11:51 AM
DDT's reputation seems to now be officially rehabilitated. My generation was the one that grew up with school books praising the environmental movement's success at banning the substance. It's been quite informative to watch that achievement's perception transform from a species-saving event to something that has directly contributed to the deaths of more children than all the environmental catastrophes in modern history combined.
And Glenn can be funny! Whodathunkit?
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Well, I would argue that DDT was misused, resulting in species threats, then after it was banned, it was used more responsibly. I don't think it makes sense to argue that banning its widespread agricultural use contributed significantly to an increase in malarial illness. On the contrary, it was banning its ag use that has enabled its continued use in homes, since the widespread application would have caused increased resistance in mosquitos.
Speaking as one who just saw a live Bald Eagle as I was driving down the GW Parkway at Monday afternoon's rush hour, and all the other waterbirds and birds of prey, I'm glad the shit's gone in the US.
While I'm sorry that mosquito infestations have returned in some parts of the world thanks to the ban, that only means that more research is needed to find a better pesticide that doesn't linger on in the environment...
Well, the problem with that is the new pesticide will cost more than DDT, probably much more. It's cost, not capability, that keeps the developing world from using pesticides other than DDT.
I'm not completely sure the resistance argument is valid in the case of insects, but it's an interesting point.
Resistance to factors such as this follows this general model:
-Every generation of off-spring have mutations
-A very small percentage of those are actually useful (the rest are benign as they occur in junk DNA or deadly and you get no development of the embryo/egg/whatever).
-If there are no environmental selectors for that mutation, it likely dies out or stays at a very small level in the overall population.
-However, if you introduce some sort of environmental selection, those best capable of dealing with the change live and reproduce.
How does that transfer here? Same way we do it for cellular markers. You introduce some chemical or other factor at a level high enough to kill almost everything (99.9% or so). What's left over tends to be resistant to said selector. So, DDT gets used, but no properly. It kills almost everything, but not quite.
To make it work, you've got to have huge numbers of offspring - and it works even better with monoclonal populations like bacteria, yeast, etc. Mosquitoes and improper DDT use would work. However, to be fair - the same would be true of any pesticide we're using.