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.
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.
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.
Dealing with malaria in the last 60 years is seen by the author in the perspective of his own experience. His malaria work, which began in 1941, covered the study of the habits of the mosquitoes dwelling in the savanna country of Eastern Colombia and the effect on malaria transmission of the newly introduced DDT residual spraying. The success of the campaign he later directed in Sarawak and Brunei contributed to the launching by WHO of its global malaria eradication campaign. Further successful work in Uganda showed the possibility of effective control and even eradication in highland country but left unsolved the problem of how to interrupt transmission of holoendemic malaria in Africa. The author's work with WHO in the Middle East showed to what extent social and economic conditions could influence the course of a malaria campaign. This was also the experience in America, both in Colombia in the author's early work and later in Mexico during an evaluation of the national malaria programme. Development of insecticide resistance was also encountered in his career and the refractoriness of the European vectors was also observed in his work as a malariologist.
DDT indoor residual sprayings in the Province of Central Java, Indonesia, for the past 28 years are reoieuied in terms ofAnopheles aconitus resistance to DDT and incidences of malaria. DDT resistance by An. aconitus has continued to increase and spread since its first detection in Central Java in 1962. In most areas malaria transmission is perennial, which appears to be not interrupted by DDT residual spraying of inner walls because of DDT resistance. In searching for alternatives to DDT, fenitrothion was the most effective residual compound among five insecticides tested in village scale trials, giving control for about 13 weeks at 2 g/m2. Because the target species rests largely on the lower portions of walls, when applied at 2 g/m2 to only one horizontal swath between 10 and 85 cm from the ground, this compound was effective for over two months, about one-third less than that found in full coverage applications. For a single application this selective method reduced the amount of insecticide by 65 percent and manpower by 43 percent, and three applications, to compensate for less residual effectiveness, will reduce insecticide use by about 50 percent and manpower by 15 percent, compared to two applications with full coverage. Further field investigations on application of insecticides and the ecology of the DDT-resistant vector continue to be needed in Central Java to reduce further the cost of residual sprayings in malaria control programmes. This review also suggests the possibility of other selective spraying methods and anti-vector methods applicable at the village level by the community.
A survey of 308,101 schoolchildren conducted in 10 of 11 states in Peninsular Malaysia revealed that 10.7% have Pediculus humanus capitis infestation. The results of treatment with 1%, 2% and 5% DDT in coconut oil in 374 cases reveal cure rates of 3.5%, 15.8% and 51.3%, respectively, suggesting that the head louse has probably developed resistance to this insecticide in Malaysia.
Susceptibility tests were carried between 1987-1989 on Anopheles maculatus female adults collected from twelve different localities in Peninsular Malaysia to DDT. Mosquitoes collected from all localities except those from Kuala Berang, Trengganu state were found to be susceptible to DDT when tested with 4% impregnated paper. Several factors contributing to the lack of development of resistance despite many years of residual spraying in Peninsular Malaysia include exophily, exophagic and excito-repellency behaviour of An. maculatus and the inadequate spraying coverage of houses.
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.
The presence of endocrine disruptors in source water is of great concern because of their suspected adverse effects on humans, even when present at very low levels. As the main source of potable water supply, rivers in Malaysia are highly susceptible to contamination by various endocrine disruptors originating from anthropogenic activities. In this study, the contamination levels of 1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane (DDT) and its metabolites and di-(2-ethylhexyl) phthalate (DEHP) in rivers of Selangor were examined using gas chromatography-mass spectrometry. Samples were collected from sites representing source water for 18 drinking water treatment plants in Selangor between July 2008 and July 2009. DDT and its metabolites were detected in only 14% of the 192 samples analysed at levels ranging from 0.6 to 14.6 ng/L. Meanwhile DEHP was detected in 96.8% of the samples at levels ranging from below quantitation level (18 ng/L) to 970 ng/L. The detected levels of DDTs and DEHP were lower than the WHO and Malaysian Guidelines for Drinking Water Quality. Data obtained from this study should also serve as a reference point for future surveillance on these endocrine disruptors.