DDT should be sprayed on water pools, tents, and on people themselves—as indeed was once common in Sri Lanka and throughout most of the world.
Unfortunately, mosquitoes in Sri Lanka are resistant to DDT, so DDT spraying would be a waste of time and money.
Fumento insists that DDT spraying would be effective despite resistance because
Resistance doesn’t mean “immunity.” Often it simply means using more insecticide in the spray than you would otherwise.
And then when you do that, the mosquitoes evolve resistance to the
higher dosage. Sri Lanka switched from DDT to Malathion in the 70s
because DDT was no longer preventing malaria.
Further, because resistance is a drain on an insect’s physiology, after a time that resistance begins to fade. It has certainly been long enough since mosquitoes in those areas were sprayed with DDT that many will have lost resistance.
However, since there are some DDT-resistance genes still on the population, the whole population would quickly become resistant once DDT is sprayed.
Mosquitoes “are almost certainly not going to become immune to DDT’s most valuable attribute: its repellency,” writes DDT expert Paul Driessen. Even in tiny quantities “DDT keeps up to 90% of the mosquitoes from even entering a home. It irritates those that do come in, so they don’t bite; and it kills any that land on the walls, before they can infect another person. No other insecticide, at any price, can do that or do it for six months or more with a single application.”
Paul Driessen is not an expert on DDT, entomology, malaria or tropical
medicine. His area of expertise is public
Nor is his statement relevant—DDT does not kill resistant
The Journal of Vector Borne Diseases last June concluded: “The overall results of the study revealed that DDT is still a viable insecticide in indoor residual spraying owing to its effectivity in well supervised spray operation and high excito-repellency factor.”
But if you look at the full
paper you will find that
the study was conducted in India and not Sri Lanka and that the
mosquitoes were only partly resistant to DDT. Sri Lanka switched from
DDT to Malathion in the 70s because the mosquitoes were fully
resistant and DDT was no longer preventing malaria.
In any case, even if DDT was still somewhat effective against
partially resistant mosquitoes it would be still not necessarily be a good idea to use it, because other insecticides are more effective in such circumstances. Professor C F Curtis of the London School of Hygiene and Tropical Medicine wrote:
Deltamethrin and cyfluthrin were found to be much superior to DDT, HCH or malathion in vector control in trials in India (Ansari et al., 1990; Schofield, 1993). However, these data are not entirely relevant to the question under discussion because they were in areas where the vector (An.culicifacies) was resistant to DDT, and it should be recalled that the W.H.O. recommendation of the use of DDT only applies to susceptible populations (W.H.O., 1984).
That’s why the real experts on DDT don’t recommend that it be used where the
mosquitoes are resistant. Nor, for that matter, does the World Health Organization or any other
expert recommend that be sprayed on people or pools of water as
Fumento proposed. Fumento is just out of his depth on this topic.