Investigations on the contact of the legs of anophelines with resting surfaces and its effect on susceptibility to insecticides.

Observations of resting anophelines have shown that the third pair of legs has the greatest area in contact with the surface on which the mosquito rests and the forelegs the least contact. Susceptibility tests with mosquitos from which one or another pair of legs has been removed indicate that absence of the hind legs has a considerable effect on the pick-up of toxicant. With DDT the removal of this pair gave an LC(50) four times greater than removal of the forelegs. With dieldrin the difference was less, presumably owing to the fact that there is less irritability with this insecticide and hence the mosquito remains quieter, taking off and settling less frequently. These observations point to the need to use mosquitos with no legs missing when carrying out susceptibility tests.