easily wets and penetrates the insect cuticle (outer covering). In residual spraying, the
solvent evaporates from treated surfaces, leaving a deposit of the insecticide in
relatively pure form. Disadvantages of solutions are that they are readily absorbed
through the skin; the solvents are flammable and relatively expensive; they stain; and
they are, in general, toxic to vegetation.
Emulsions are prepared by diluting emulsifiable concentrates with water and
thoroughly mixing. The emulsifiable concentrate is a concentrated solution of the toxic
agent in a solvent to which an emulsifying agent (wetting agent, such as soap or a
detergent) has been added. The emulsifying agent enables the small droplets of
solvent carrying the toxicant to remain dispersed through the water, much like the fat
globules in homogenized milk. The emulsion, like the solution, need not be constantly
agitated. This advantage, combined with that of a cheap, readily available diluent
(water), makes the emulsion a commonly used pesticide formulation in the Army.
Emulsions are similar to solutions in their effects on insects and they can be used for
most residual spraying. They do not usually stain surfaces. Their principal
disadvantages are that they are readily absorbed through the skin and that they may be
toxic to plants.
a. Figure 2-1 summarizes the basic constituents which combine to form a dust
(1) Dust -- a technical grade insecticide plus an inert carrier.
(2) Suspension -- an insecticidal dust plus a wetting agent plus water.
b. Figure 2-2 summarizes the basic constituents that combine to form a
solution or emulsion.
(1) Solution -- a solution concentrate consisting of a technical grade
insecticide and a solvent, plus a diluent.
(2) Emulsion -- an emulsifiable concentrate consisting of a solution
concentrate and an emulsifying agent, plus water).
The preparation of wettable powders and emulsifiable concentrates is
accomplished by the manufacturer before the pesticides are procured by the Defense
Supply Agency. Mixing by using personnel is normally limited to mixing an appropriate
diluent with standard pesticides, issued through military supply channels, in one of the