When measuring the extent to which indoor application of insecticides contributes to pollution of the overall environment, other uses of insecticides must be added into the calculations. Actually agricultural uses (though now drastically curtailed) account for by far the largest proportion of residual DDT in the environment. In terms of absolute amounts, agriculture uses 80 times as much insecticide in a given area as a malaria program. The additional fact that very little DDT from this intradomiciliary application even enters the outdoor environement should also be considered. Thus, we conclude that the DDT applied indoors in malaria programs is a relatively minor source of pollution.
DDT is variable in its effects on animals and birds, for reasons of both physiology and behavior. Of course, house spraying eliminates insects other than mosquitoes, such as cockroaches. The toxic effects on human beings are not known, since few harmful effects have ever been noted. Actually, the principal ecological consequence of the use of insecticides has been the development of insecticide-resistant vector populations; frequently such resistance has been the product of agricultural uses.
Where resistance to residual adulticides has occurred, substitution of larvicides has been attempted, but of course damage to organisms other than mosquitoes must be guarded against. Several organophosphorus larvicides are being evaluated with regard to safety and effectiveness. Of these, Abate is the larvicide of choice where water is used for drinking.
Research now underway in the so-called problem areas stresses source reduction rather than interruption at the man-vector point of contact, and represents a return to a many-sided approach. Insecticide use, like every other aspect of malaria and malaria control, has implications for bionomics and ecology.