Ortho-isopropoxphenyl methylcarbamate (OMS-33) as a residual spray for control of anopheline mosquitos. With special reference to its evaluation in the WHO programme for evaluating and testing new insecticides.

Bull. Org. mond. Bull. Wid Hlthi Org. ) 1969, 40, 67-90 Ortho-Isopropoxyphenyl Methylcarbamate (0MS-33) as a Residual Spray for Control of Anopheline Mosquitos With Special Reference to its Evaluation in the WHO Programme for Evaluating and Testing New Insecticides JAMES W. WRIGHT,1 ROY F. FRITZ,2 KAY S. HOCKING,3 ROBERT BABIONE,4 NORMAN G. GRATZ,2 RAJINDAR PAL,2 ALAN R. STILES 2 & MILUTIN VANDEKAR2 More than 1300 compounds have so far been included in the WHO Programme for Evaluating and Testing New Insecticides, which is designed to disclose compounds that may satisfactorily replace those to which insect vectors of disease have become resistant. The authors describe the successfulpassage of o-isopropoxyphenyl methylcarbamate (OMS-33) through the first 6 stages of the 7-stage programme that has been establishedfor compounds intendedfor use against anopheline mosquitos and conclude that this product is suitable for testing in the final stage-large-scale epidemiological evaluation. In operational field trials (at 2 g/m2) OMS-33 has been shown capable of controlling Anopheles stephensi (in Iran), An. gambiae and An. funestus (in Nigeria) for 3-4 months, An. albimanus (in El Salvador) for 2-4 months and An. dthali (in Iran) for 21/2 months. It has an airborne effect by which anophelines are killed for a considerable time after OMS-33 has been sprayed, even though they do not make contact with a sprayed surface; this quality would appear advantageous in areas where anophelines enter houses and bite man but do not rest long enough on sprayed surfaces to acquire a lethal dose of insecticide or where significant outdoor biting occurs. The observance of simple safety precautions protects occupants of sprayed houses, spraymen and others from danger. Chemical studies have indicated that commercially produced water-dispersible powders of OMS-33 are stable under field conditions of storage and use. Prior to the introduction of residual insecticides, malaria was controlled only in certain areas where the population density and good economic conditions permitted. The discovery of synthetic organic insecticides such as DDT, dieldrin and HCH made it possible for the first time to consider the eradication of malaria on a world-wide basis, since these relatively inexpensive insecticides have a persistent I Chief, Vector Biology and Control, World Health Organization, Geneva, Switzerland. 'Vector Biology and Control, World Health Organization, Geneva, Switzerland. ' Consultant, Vector Biology and Control, World Health Organization, Geneva, Switzerland. ' Malaria Eradication, WHO Regional Office for the Americas, Washington, D.C., USA. 2277 -67 toxicity which lasts for many months after application. However, the emergence of resistance of malaria vectors to DDT, dieldrin and HCH in certain parts of the world has seriously modified progress and in some situations has become one of the major obstacles to achieving the goal of malaria eradication. Despite intensive research to overcome the problem of resistance, the use of alternative insecticides remains the only solution at present available. Therefore the World Health Organization is making a great effort to develop insecticides other than those to which resistance has occurred. The WHO collaborative programme for the evaluation and testing of insecticides is based on 1. W. WRIGHT AND OTHERS 68 FIG. 1 WHO PROGRAMME FOR EVALUATING AND TESTING NEW INSECTICIDES Pesticide Manufacturers SOURCE and University Laboratories STAGE 1 University of Califomia, Riverside, Califomia, USA ENTOMOLOGY (Preliminary Laboratory Tests) Toxicology Research Unit, Medical Research Council Laboratories Carshalton, Surrey, England TOXICOLOGY STAGES II and Ill Entomology Research Division, US Depadnment of Agriculture, (Laboratory and Smulated Gaimesuile, Florida, USA National Communicable Disease Center, US Depadmrent of Health, Education and Welftae, Savannah, Georgia, USA ENTOMOLOCY_ENTOMOLOGY Tropical Pesticides Research Unit, Down, Hilts., England Podton ENTOMOLOGY FiLdb Tests)yadSmltdGieNTOMO,loGYa,US E N T O M O L OGC Y F e d T e stf. s ) National Communicable Disease Center, Research Division, Entomology US Department of Health, Education STAGE IV US Departmrent of Agriculture, Welfare, Florida, USAand USA aronsuie, (Field Tests) (Field Tests) Gaineville, Savannah, Georgia, USA PTonida, l| ENTOMOLOGY STAGE V STAGE V (Village Trial) Research Institutt Tropical PesticidesTanzania Afusha, ENTOMOLOGY ENTOMOLOGY WHO Anopheles Control Research ~DATn No. I ENTOMOLOGY Scientifique Office de Ia Recherche Outre-Mer, xl Technique Centre IAraz, Upper Volta Bobo-Dioulasso, ENTOMOLOGY WHO/AMRO Insecticides Testing Team El Salvador Kaduna, Nigeria ~~~~~~~~~~~~Lagos/ ENTOMOLOYY T CHEMICAL FORMULATIONS STAGE VI (Operational Field Trial) WHO/AMRO Insecticides Testing Team, El Salvador WHO Anopheles Control Research Unit No. 2 WHO/AMRO Insecticides Testing Team, Iran El Salvador ENTOMOLOGY TOXICOLOGY OPERATIONAL EXPERIENCE STAGE VII (Large-scale Trial) WHO Nrgeria, Uganda etc. EPIDEMIOLOGY newly developed insecticides submitted by the chemical industry to WHO.' These compounds are evaluated by a number of laboratories throughout the world working in collaboration with WHO in a programme of 7 stages, leading from investigation under carefully controlled laboratory conditions to large-scale tests in the field (Fig. 1). Stage I of the programme involves the laboratory evaluation of the toxicity of new compounds to 1 A comprehensive account of the programme and of the evaluation of a very large number of compounds during the period 1960-67 is contained in unpublished working document WHO/VBC/68.66. A limited number of copies of this document is available to persons officially or professionally interested on request to Distribution and Sales, World Health Organization, 1211 Geneva, Switzerland. mosquito larvae and adults and to houseflies. In these screening tests strains of insects both resistant and susceptible to DDT and dieldrin are used. Consideration of the possible human hazard of the new chemical also begins at this stage, with a review of the toxicity data furnished by the manufacturer. In the next stages, 3 laboratories evaluate the compounds which have shown promise at Stage I on additional species of insects in the laboratory (Stage II) and under simulated field conditions (Stage III). Appropriate tests are carried out against mosquito larvae and adults, houseflies, blackflies, fleas, bed-bugs, lice, Triatoma and ticks, with various methods of application. Concurrently, the intrinsic mammalian toxicity of the new compound is established by animal tests. OMS-33 INSECTICIDE AS RESIDUAL SPRAY FOR ANOPHELINE CONTROL Prior to Stage IV medical toxicologists determine a priori safety precautions necessary to protect spraymen and villagers from any hazard due to the insecticide. During the actual spraying of insecticide (...truncated)