1. 1. Paris green was used as a larvicide on an inland hilly estate where A. maculatus was the carrier-and where most of the water treated was moving, more or less rapidly. 2. 2. Three different diluents were tried, viz., lime, talcum and soapstone powder. 3. 3. The strength of the mixture was one part of Paris green to ninety-nine parts of diluent by volume. 4. 4. Distribution was carried out by mechanical blowers and sprayers. 5. 5. The application was checked twenty-four hours afterwards. For one month it was checked forty-eight hours afterwards. 6. 6. There was an increase in breeding places-most of which were found in moving water. 7. 7. There was an increase in larvæ, many of them being over two days old. 8. 8. In spite of treatment of epidemics with plasmochin and quinine, the malaria rate was higher than during the previous year. The rise was more or less consistent, pointing to constant infections. 9. 9. The morbidity rate, death rate and infantile mortality were apparently not adversely affected, but in view of the treatments given with plasmochin, they are of no help in deciding the value of Paris green. 10. 10. There was a distinct fall in anti-larval costs, but the total anti-malarial costs were still high on account of the treatments necessary for epidemics of malaria. 11. 11. The advantages and disadvantages of Paris green are discussed.
This work, carried out on a rubber estate in Malaya during 1949, was a Continuation of the trials begun in 1948 previously recorded [this Bulletin, 1949, v 46, 1116]. Full details concerning the terrain and the nature of the experiment were given in the previous publication. In 1949 the malaria rate in the area approached the rates which were customary in pre-war years, for the first time since the reoccupation of the country. The Indian population which was chosen for the experiment contains the survivors of the Japanese occupation; many had been in Siam and almost all had suffered from malaria. Treatment had been entirely lacking or very inadequate, with the result that the survivors had developed a high degree of immunity by the end of the war. These facts probably explain the low incidence of malaria in post-war years in spite of high prevalence of A. maculatus. No anti-larval measures have been carried out since 1941. Neo-premaline completely suppressed malaria in one group, the control group showing a high incidence. In other groups chloroquine, or chloroquine and pentaquine combined, given once a week, promptly brought to an end primary waves of malaria which were rising rapidly.
1. Several experiments were carried out in the field and in the laboratory with various insecticides against A maculatus. 2. Almost all the mosquitoes that came into contact with surfaces sprayed with DDT preparations died in less than 30 hours but the length of life varied with the preparation and depended on various factors that are mentioned. Control mosquitoes lived almost twice as long. 3. Gammexane Dispersible Powder (P 520) killed in a much shorter time than the DDT preparations and holds out a greater hope of success in controlling ‘A maculatus’ malaria with insecticides. 4. It is difficult to assess the value of insecticides in any one year in areas where breeding of the vector is intense. The results of long term field experiments, under strict control, are awaited. 5. Meanwhile, Mass Suppression with drugs still remains the method of choice – in this area.