> Blane White
> MN Dept of Agriculture wrote:

> Just a comment:  The reason DDT is no longer used for vector
>  control is that is no longer works - resistance has developed.

In the Science News article
http://www.sciencenews.org/20000701/bob2.asp
it was stated that:

"In many  regions the insecticide [DDT] has performed
dependably, with no sign of mosquitoes developing resistance,
observes Donald R. Roberts of the Uniformed Services
University of the Health Sciences in Bethesda, Md."

"although DDT can kill mosquitoes, the new study
suggests that it primarily protects by repelling them.
Comparing DDT's killing action with that of other
pesticides used for malaria control‹the standard practice
for 55 years‹may be the wrong measure of its value"

"John P. Grieco, who is also at the Uniformed Services
University,  finds that deltamethrin‹the insecticide usually
held up as the leading alternative‹doesn't come close to
matching DDT's performance."

"In and around a trio of dirt-floor, thatched huts in
southern Belize, Grieco monitored the behavior of the
malaria-carrying mosquito Anopheles vestitipennis.
Mosquitoes entered an untreated hut at dusk and left at sunrise.
 After the interior walls of a second hut were sprayed
with deltamethrin, the mosquitoes entered at dusk but
left by midnight. As expected, Roberts notes, "the whole
time they were inside, the mosquitoes were biting [us]."

"However, DDT sprayed inside the third hut repelled the
flying bloodhounds. Only 3 percent as many mosquitoes
entered the DDT-sprayed hut as the other two. Of those
few mosquitoes that did venture in, most exited without
biting."

Paul Cherubini