> 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