Observations on Mosquito Behaviour in Native Huts

Extract

Mosquitos continue to enter occupied, untreated native huts throughout the night, with peak periods of entry at dusk and dawn. Early morning mosquito catches do not give a true picture of the numbers entering and leaving huts during the night.

In a series of catches 63 per cent. of 5,576 mosquitos and 79 per cent. of 506 Anopheles gambiae were caught resting on the underside of the thatch roof.

By using five traps inserted in apertures one foot below the top of the wall, the numbers of mosquitos attempting to leave a hut were determined. Of 1,014 mosquitos entering huts before 10 p.m., 63 per cent. remained inside until 6.30 a.m., that is for 8½ hours. Catches to estimate numbers entering and leaving at different times during the night were also made.

Treatment of huts with DDT wettable powder and DDT-kerosene solution did not interfere with the normal behaviour of mosquitos as far as entry was concerned. Biting occurred in the treated huts.

The DDT wettable powder appeared to be more effective than the DDT-kerosene solution.

Some mosquitos entered the treated huts, fed and then left before acquiring a lethal dose. After making contact with treated surfaces mosquitos became restless but, under the conditions existing in the huts during the experiments, activation did not result in more leaving the treated huts than the untreated one. Unfortunately there were few A. gambiae and the predominant species entering the huts was Taeniorhynchus fuscopennatus.

Some of the female A. gambiae released into unoccupied DDT-treated huts escaped into the traps before acquiring a lethal dose. Although there was a tendency for more to enter the traps of a DDT-treated hut than those of an untreated hut, the data are insufficient to show a significant difference.

The majority of mosquitos entering the traps did so within one hour of their release.

No mosquitos were still alive 12 hours after their release in huts treated 17 weeks previously with DDT wettable powder or DDT-kerosene solution, or in the hut treated 12 weeks previously with "“Gammexane” wettable powder.