A veranda-trap hut for studying the house-frequenting habits of mosquitoes and for assessing insecticides. III. The effect of DDT on behaviour and mortality

Abstract

The effects of DDT on the behaviour and mortality of Anopheles gambiae Giles, A. funestus Giles, Mansonia uniformis (Theo.) and Culex pipiens fatigans Wied., entering experimental huts, have been studied with the assistance of gas-chromatographic techniques.Sixty to 70% of A. gambiae and 70–80% of M. uniformis were deterred from entering verandah-trap huts treated indoors with a nominal dosage of 200 μg/cm2 of DDT active ingredient. Gas chromatographic techniques indicate that the chemical basis of the deterrency was a steadily diminishing outflow of DDT from the hut, either as a dust or vapour, and the build-up of deposit on the untreated overhanging eaves to 0·02 to 0·27 μg/cm2 seven months after treatment. A. funestus was less deterred than A. gambiae and M. uniformis, but the behaviour of C. p. fatigans was almost unaffected by the DDT deposit.Overall mortalities were highest in A. funestus and M. uniformis, lower in A. gambiae and extremely low in C. p. fatigans.There was a marked irritant effect of the DDT deposit on recently blood-fed A. gambiae, some 50–70% being driven out of the treated huts. This behaviour occurred to a lesser degree in A. funestus but was absent in M. uniformis and C. p. fatigans. The chemical basis of the irritant effect was indicated to the extent that surviving mosquitoes, that left the treated hut, showed 1·5 ng/insect of DDT. Mosquitoes that died, whether indoors or after leaving the hut, picked up amounts ranging from 7 to 20 ng/insect.

Efficacy of indoor residual spraying with dichlorodiphenyltrichloroethane against malaria in Gambian communities with high usage of long-lasting insecticidal mosquito nets: a cluster-randomised controlled trial

“…The effectiveness of DDT is thought to be partly due to its insecticidal activity, but it is also considered to be a spatial repellent, reducing the entry of mosquitoes indoors, and a contact irritant, increasing the rate at which mosquitoes leave a sprayed room 12 .…”

“…DDT, the most persistent insecticide used for spraying 11 , is considered both a spatial and contact repellent 12,13 . If this is so, the repellent effect of DDT may reduce the contact of mosquitoes on LLIN and since LLIN reduce bloodfeeding, fewer blood-fed mosquitoes may rest on sprayed surfaces.…”

Indoor residual spray and insecticide-treated bednets for malaria control: theoretical synergisms and antagonisms

“…Specifically we want to compare the insecticides that have the greatest longevity-DDT and pyrethroids [8]. DDT is a strong repellent, deterring mosquito entry into a sprayed house [9,10], whereas pyrethroids have little repellence [16]. For simplicity, we assume the extent to which mosquito entry is deterred decays equivalently to the mosquito-killing efficacy of the insecticide, w. The proportion of humans protected by IRS with DDT is the product of w and the proportion of houses sprayed, g. Following empirical evidence of the overwhelming percentage (.90%) of indoor collected A. gambiae females being bloodfed [17], we assume that a mosquito comes into contact with IRS only if it has consumed a blood meal.…”

“…IRS with pyrethroids kills mosquitoes that rest on sprayed walls after they have bloodfed. IRS with DDT has the additional function of deterring mosquito entry into sprayed houses (or promoting their rapid exit) [9,10]. ITNs primarily reduce mosquito bites on humans and cause additional mosquito mortality through contact.…”

Experimental hut evaluation of the pyrrole insecticide chlorfenapyr on bed nets for the control of Anopheles arabiensis and Culex quinquefasciatus

“…Experimental hut evaluation was carried out at Mabogini field station, Moshi, Northern Tanzania in three experimental huts constructed according to a design described by Smith (1965) and Smith and Webley (1969). Some slight modifications were made involving reduction of eave space, addition of cardboard and hessian cloth ceiling, concrete floor surrounded by a water filled moat, and improved screening of the veranda.…”