Field experiments on the behavior of malaria vectors in an unsprayed hut and in a hut sprayed with DDT in Northern Nigeria.

Investigations on the behaviour of malaria vectors in DDT-sprayed houses are of special interest in malaria control campaigns. In the Northern Region of Nigeria the behaviour of the local vectors was studied by means of experimental huts fitted with exit window-traps. The results obtained show a marked reduction in the number of mosquitos entering the sprayed hut and a depression of the biting rate. The most striking observation is the large number of A. gambiae and of A. funestus that left the sprayed hut and the considerable proportion that escaped unharmed. Both figures show a very marked increase in subsequent months after spraying, indicating a rapid loss of the lethal action of the DDT residue along with a long-lasting irritant effect. It is concluded that under the particular local conditions the application of 1.9 g/m(2) DDT twice a year may not be sufficient to interrupt malaria transmission in the Northern Region of Nigeria.