Facts are presented which suggest that mosquitoes of the Anopheles barbirostris species group that gave me a very uncomfortable night in 1941, whilst serving with the Volunteer forces, were probably A. donaldi. This species is now known to be a vector of human filariasis and probably malaria. Some of the steps are described by which I was led, sixteen years later, to recognise and later name donaldi as a new species. Reasons are given for thinking that around 1918 A. donaldi was present in some numbers at the railway town of Gemas where malaria was a serious problem. H.P. Hacker made a survey at Gemas in 1918 and though the principal vector was probably A. maculatus, 'umbrosus' and 'barbirostris' were the commonest larvae he found.
Anopheles donaldi Reid, a member of the A. barbirostris species group, is a vector of human filariasis and probably malaria. The discovery of some old specimens of this species, collected in Kuala Lumpur town where it no longer occurs, together with evidence from the literature about past malaria in the town, suggest that donaldi may have played a part in transmitting that malaria.
After two years' use of hexachlorocyclohexane (BHC) as a larvicide in Georgetown, on Penang Island, control of Culex fatigans breeding became unsatisfactory. Two laboratory colonies of fatigans were established, one from Georgetown, and one from Kuala Lumpur where no insecticides had been used; tests were then made to determine the median lethal concentrations (MLC) of BHC, dieldrin, and DDT for the larvae of the two strains. The Georgetown strain was found to have acquired a tenfold resistance to BHC, and also to dieldrin to which it had not been exposed, but it showed no significant increase of resistance to DDT, to which it had also not been exposed. A year later, when both strains had passed through some ten generations in the laboratory without exposure to insecticides, the Georgetown strain was found to have lost much of its resistance to BHC, although the MLC was still twice that of the non-resistant Kuala Lumpur strain.