Field experiments have been made with DDT in oil as a larvicide on flowing water against Anopheles maculatus. 1. In unweeded drains and streams, 2 oz. DDT per acre applied evenly with a pipette as a 5% solution in Malariol, gave control 1 day later of over 900%. 2. The same dose in an oil (Malariol H S) with a very high spreading pressure (33 dynes/cm) when applied at intervals of 30 yards gave only 50% control. When applied evenly control was 98%. When applied at intervals of 22 yards (one chain) in a grassy roadside drain, control was 61% before the drain was weeded and 73% afterwards. The DDT in oil when applied at intervals was prevented from reaching all the larva e by strong surface films, obstructions and side pockets, and it is clear that to control A. maculatus application must be continuous and not at spaced intervals. 3. Continuous application by spraying with a Mish pump was compared with even distribution of the same dose with a pipette. Control by pipette was only 72% on this occasion, due probably to a heavy growth of weeds, but control by spraying was considerably less, only 56%, apparently because much of the fine spray was blown away before reaching the water. The sprayer was very tiring to use. 4. DDT in Malariol with a spreading pressure of about 20 dynes/cm was compared with DDT in Malariol H S (S P about 33 dynes/cm). Both solutions were applied at intervals of 30 yards at the rate of about 2 oz. of DDT per acre. Control 1 day later was 84% with DDT in Malariol H S and 78% with DDT in Malariol. It is concluded that under the adverse conditions of these experiments (drains not weeded or maintain ed, DDT applied at intervals), better control is obtained by using oil with a very high spreading pressure. 5. Doses of about 4 ounces and 2 ounces of DDT per acre were compared. Application was by even distribution with dropping bottles. The heavier dose gave somewhat better immediate control, and had a better lasting effect, delaying the reappearance of large larvae (4th instar), usually until later than the sixth day after treatment. 6. DDT in Malariol applied evenly with dropping bottle at about 4 oz. DDT per acre was compared with ordinary oiling with a knapsack sprayer at about 23 gallons per acre. The experiment was made in weeded and well maintained drains in the Kuala Lumpur oiling area. Both treatments gave complete immediate control, no larvae being found two days afterwards, but breeding recovered a little more rapidly after the DDT treatment, though there were no large larvae on the sixth day. 7. Numerous readings were made of the strength of natural surface films on the water of breeding places. The results show a fair measure of agreement with those obtained in West Africa by Toms. The commonest film strength was found to be 7.5 – 13.0 dynes/cm., but the proportion stronger than this varied from place to place. The readings from the breeding places of A maculatus suggest that for an ordinary anti malarial oil a spreading pressure close to 25 dynes/cm will usually be sufficient. 8. It is concluded that DDT in oil at about 4 oz. of DDT per acre (=½gal of a 5% solution) can give satisfactory control of A maculatus, especially in properly maintained drains. However, the solution must be applied evenly, and with such small quantities there seems as yet to be no method of doing so which would be suitable for general use. Possible ways of overcoming this difficulty are discussed.
A first experiment on malaria control in the interior of Borneo by spraying with residual insecticides is described. The work was carried out in the isolated, sparsely populated valleys of the Baram River and its tributary, the Tinjar, in northern Sarawak. The experimental area was divided into three parts: a DDT test area, where a 75% suspension of wettable powder was applied at the rate of 2 g of DDT per m(2) of surface; a BHC test area, where a 50% suspension of wettable powder was applied at the rate of 0.10 g of gamma isomer per m(2); and a check area.Entomological investigations made before the spraying operations were started showed that Anopheles leucosphyrus Dönitz, 1901 was the main malaria vector in both the test and the check areas. Out of a total of 7568 A. leucosphyrus dissected, 30 gland infections were detected-a sporozoite-rate of 0.40%. A. barbirostris was found to be a secondary vector throughout the experimental area.THE RESULTS OF INSECTICIDE SPRAYING WERE SATISFACTORY: in the DDT test area, the spleen-rate fell from 51.8% to 25.1%, and the parasite-rate from 35.6% to 1.6%, in 21 months, and a similar reduction in the rates was observed in the BHC test area. In the check area, the spleen- and parasite-rates rose during the period of observations. It is considered that if such a degree of control can be obtained in 21 months, complete eradication can be expected in the near future.Although BHC spraying proved effective, the fact that it has to be repeated every three months makes it impracticable in the interior of Sarawak, where communications are very poor and difficulties of transport very great. DDT spraying, which need only be done twice a year, is therefore to be preferred. The cost of the DDT operations-US$ 0.45 per person protected per year-is comparatively high, owing to the difficulty of communications and to the necessity for spraying not only the village "longhouses", but also the temporary shelters which the semi-nomadic people in the interior of Sarawak build each year in the rice-fields.
Colonies of three strains of Aëdes aegypti resistant to DDT were obtained from Trinidad, Haiti and Malaya and reared beside a normal colony. From their relative resistance to a series of compounds analogous to DDT, characteristic resistance "spectra" were obtained. The two colonies from the West Indies showed a similar type of resistance, rather different from the (smaller) resistance of the Malay strain. No resistance to methoxychlor or dieldrin was found.
The yellow fever mosquito Aedes aegypti has developed resistance to DDT in the Caribbean region and in South-East Asia, but not in West Africa. Therefore West African strains were compared with South-East Asian strains for their response to laboratory selection with DDT. It was found that West African strains were much slower to respond initially, but eventually could build up a high degree of DDT-resistance. By crossing and backcrossing with a susceptible marker-gene strain, it was found that this resistance was due to a single gene linked with the gene y (yellow) on chromosome 2 at a cross-over distance of approximately 35 units in an Upper Volta strain as in a Bangkok strain; interstrain crosses indicated that the gene was the same as that in a Trinidad strain and in one from Penang. Dieldrin-resistance could be readily induced in the Upper Volta strain and proved to be due to a gene also linked with y but at a crossover distance of approximately 25 units, comparable to that in Caribbean strains previously studied. Material from Karachi, West Pakistan, developed a dieldrin-resistance also showing 25% crossing over with y, and a DDT-resistance also linked with this chromosome-2 marker gene.
In certain areas of Sabah, East Malaysia, local houses are frequently built without walls or with incomplete walls. Also, the people in these areas often refuse permission for their houses to be sprayed inside with insecticide (DDT). These special conditions are the reason for the persistence of malaria transmission under a WHO malaria eradication programme.Field trials were conducted in specially constructed huts, similar to the local houses, in which all-night collections of mosquitos were made, both those biting human baits and those resting on walls, in order to determine (1) the effectiveness of spraying DDT in houses without, or with incomplete, walls; and (2) the best way to protect people against mosquito bites with DDT-spraying where the house-owners have refused indoor spraying.The results indicate that (1) as expected, DDT-spraying inside a hut with incomplete walls is less effective than in a hut with complete walls, especially 6 months or more after spraying; (2) external spraying of walls with DDT at double the normal dose (i.e., 4 g/m(2)) greatly reduced contacts between man and mosquito and thereby limited transmission of malaria.
Insecticides Abate, DDT, Dowco-214, Dursban, fenitrothion, fenthion, gamma-HCH, and malathion were tested against the field collected fourth instars larvae of Mansonia from Penang Island, Malaysia. The larvae appeared to be highly susceptible to Dursban and Abate with LC50 values of 1.54 and 1.92 parts per billion respectively. Other chemicals, in decreasing degree of effectiveness, were gamma-HCH, fenthion, P,P'-DDT, Dowco-214, fenithrothion and malathion. The potential use of these chemicals in Mansonia control was discussed. A simple method for collecting and testing Mansonia larvae was also described.
The resistant level of the houseflies to six kinds of insecticides, DDT, Resmethrin, DDVP, Baytex, Sumithion and Diazinon, was examined on the seven strains collected in Malaysia. It was found that their susceptibility is rather higher than that of the Takatsuki strain which is a standard strain in Japan. However, their susceptibility to Sumithion was the same or slightly lower than that of the Takatsuki strain. The resistant level to five of six kinds of insecticides was the highest in the strain of Cameron Highland. The values were close to Singh's data in 1973, and this means that the resistance of the houseflies to the insecticides is increasing in Malaysia.