Regulation of the Control of Anopheles of the Fluviatilis-Group by Anti-Adult Spraying

(?) At sundown there is a strong attraction to light, and most mosquitoes leave the house at this time. There is no similar reaction at dawn. (c) Marking and other experiments show that there is a considerable daily turn-over of the population in houses. (d) About 90 per cent of blood feeding takes place after midnight. After oviposition, A. minimus returns for another blood meal on the same night. (e) In fertilized females, one blood meal is sufficient for egg laying. The present first author has had in progress for the last two years a series of experiments designed to extend Muirhead Thomson's work and to observe the effect of spraying on the numbers and behaviour of eight species of anopheles, including all three species of the fluviatilis-group. These experiments are nearing completion, but the analysis and discussion of the mass of data obtained will take some time. Meanwhile the world supply position in respect of insecticidal sprays has become so acute that it is felt that the practical application of the findings from the work of Muirhead Thomson and of myself should be published in brief, as efficient control of the group can be achieved without the enormous expenditure of insecticide which is causing the present shortage. Put very briefly, the present first author's findings in respect of the fluviatilis-gYouY) are ?? {i) In a house ' caught to emptiness ' daily? 96 per cent of the fluviatilis and varuna, and 100 per cent of the minimus population the next morning is fresh fed. (ii) If the mosquito population is disturbed by catching to emptiness only once weekly, in fluviatilis and minimus 82 per cent is fresh fed and 94 per cent in varuna. (iii) With all three species the number found resting in empty houses is no more than 11 to 15 per cent of those found in inhabited houses. (iy) In a house ' baited ' only with a cow, the fluviatilis population is no more than 16 per cent of that in a similar house with a human bait, but the percentage is increased to 50 in wtwwwws and to almost equal numbers in varuna. However, as the anthropophilic index of varuna so caught is 67 per cent, compared with 81 PC1