MANUAL ON LARVAL CONTROL OPERATIONS IN MALARIA PROGRAMMES prepared by the WHO Division of Malaria and Other Parasitic Diseases WORLD HEALTH ORGANIZATION Geneva 1973 j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j List of contents Foreword l Definition of antilarval operations ................. 2 The place of antilarval operations in malaria programmes 2 Objectives of antilarval operations . 3 Methods of larval control and a consideration of their use in malaria programmes 3 Chapter I - Naturalistic control · 7 Chapter II - Source reduction . • . • . • . 15 Chapter Ill - Chemical control of mosquito larvae 65 Chapter IV - Planning and organization of antilarval operations in malaria programmes ......................... 141 References 159 Additional bibliography 162 Annex 1. Metric and English equivalents for units commonly used in mosquito larviciding operations . 167 Annex 2. Proprietary and ISO names of some pesticides 171 Annex 3. Entomological procedures and techniques for the planning and evaluation of antilarval operations . ..• 173 Annex 4. Sample procedural guide and instructions for the safe handling and use of pesticides 187 Annex 5. Some examples of equipment used for application of pesticides 195 List of figures Figure No. Title 1 Calculation of the azimuth 21 2 Grading land for surface irrigation 24 3 Sample plan and profile sheet 26 4 Typical ditch cross-section 27 5 Conventional levelling from benchmark A to point C (heights in metres) 33 6 A - Pipe or tile liner; B - Pre-cast ditch liner 35 7 Rectangular weir 37 8 Cross-section ditch for mosquito control 37 9 Measuring flow of water in a 60° V-notch weir 38 10 Discharge over a triangular weir 40 11 Patterns of salt marsh ditching 48 12 A wooden tilting bucket, counterweighted, for automatic flushing of small streams. Bucket in raised position, accumulating flush water behind dam 53 13 A wooden tilting bucket, counterweighted, for automatic flushing of small streams. Bucket in lowered position, discharging flush water 53 14 Comparison of Macdonald and Legwen-Howard automatic siphons 54 15 Diagrammatic representation of operation of Legwen-Howard automatic siphon 54 16 Measurements for several sizes of Legwen-Howard automatic siphons 55 17 Methods of installing Legwen-Howard automatic siphons in existing dams or weirs 55 18 Legwen-Howard siphon modified to actuate on a small flow 58 19 Properly protected spring (I) 59 20 Properly protected spring (II) 59 List of figures (continued) Figure No. Title 21 The chemical control of insects 7l 22 Construction of drip application equipment 128 23 Horn seeder 129 24 Theoretical paths of spray droplets of selected sizes in stable air currents of velocities 3.2, 6.4, and 9.6 km/h 136 List of tables Table No. Title 1 Profile level notes 25 2 Level notes for grade stakes 29 3 Discharge in 1/sec over a rectangular weir 40 4 Table of toxicity of some selected chlorinated hydrocarbon insecticides to female laboratory rats 73 5 Acute oral and dermal LD 50 values for female white rats of 15 organophosphorus pesticides 74 6 Some chemicals useful as mosquito larvicides 76 7 Cost comparison of seven commonly used larvicides based on weekly application (excluding operational costs) 77 8 The spreading pressure of some mineral and vegetable oils 80 9 Covering power and spreading pressure of different oils on clean tap water 80 10 Examples of emulsifiers used with specific insecticides 82 11 Physical properties of some common solvents 85 12 Per cent mortality, Anopheles stephensi larvae,, at 12, 24 and 36 hours, using different mixtures of oils and Triton X-100 detergent in water warmed to 25°/29°C 94 13 Variable factors governing rates of application and standard rates recommended for teaching spraying techniques for basic types of liquid spray equipment 114 14 Number of particles per square metre at various rates of application 117 15 Rates of coverage in hectares per hour for types of liquid spray equipment used for area application of mosquito larvicides 123 16 Characteristics of some mist blowers 125 17 Flow rates for various TeeJet orifices 127 18 Application rates 133 List of tables (continued) Table No. Title 19 A theoretical approximation of the number of spray droplets of various selected sizes in units of volume and surface area 137 20 Sample: mosquito source survey record 144 PREFACE This manual is intended for planners in malaria programmes and for all who are responsible for the execution of large-scale antimalaria operations. It provides valuable teaching material for the senior staff at malaria training centres as well as a source of reference for them and their students. Senior operational and engineering staff in malaria programmes will find it particularly useful in the planning and execution of antilarval operations, and they will be able to develop their own operational and training manuals from it. It is hoped that all malariologists will welcome it as a comprehensive reference work on antilarval operations in malaria programmes. page l MANUAL ON LARVAL CONTROL OPERATIONS IN MALARIA PROGRAMMES FOREWORD The control of malaria has been attempted mainly by attacking the parasite in man by the administration of drugs, by preventing contact between the mosquito and man, or by eliminating or incapacitating the vector mosquitos through various means. The attack on the parasite in man proved insufficient by itself to obtain the eradication of malaria; the attack on the vectors alone, without eliminating the residual reservoir of infection in humans, also failed to attain eradication. A combination of the two methods has therefore been used to advance malaria eradication. The attack on the vector mosquitos attempts to interrupt transmission through decreasing the density and longevity of the vector population, while the attack on the parasite reduces the sources of infection in man by attempting to eliminate all infective cases. Spraying with residual insecticides to destroy the adult vector mosquitos continues to be the principal operational measure employed in malaria eradication programmes. Though directed mainly against adult Anopheles mosquitos, residual spraying may involve some control of the larval stages. Due to the complexity of larval control, it alone has seldom been the method of choice in malaria eradication programmes except where imagicidal operations failed to produce effective results or where they were very much more expensive or impracticable. The malaria eradication programme is a gigantic undertaking involving almost two-thirds of the population of the world, mainly in remote areas of developing countries where complicated, highly technical and costly technology cannot be readily used. On the other hand, malaria control programmes aiming at the reduction of infection, may find it convenient or more economical to make more extended use of antilarval measures. Where the vectors are susceptible to residual pesticides, indoor spraying has the following advantages compared with other mosquito control measures: Simple: No complicated techniques or equipment are needed and unskilled workers are easily trained. Practicable: Can be performed effectively in most situations and under virtually all conditions where needed. Effective: Complete interruption of malaria transmission can be achieved in most cases. Low-cost: Annual and total cost is generally considerably lower than that of achieving the same goal by other methods. When total spray coverage with an effective insecticide was completed according to plan, malaria transmission has generally been interrupted within the expected period. However, there have been increasing failures due to technical factors; for example: (a) The mosquito vectors were not domestic, i.e. they did not feed and rest inside houses (exophagic and/or exophilic), or (b) They have been deterred from resting upon, or have been irritated b;y, sprayed surfaces, or (c) They have acquired physiological resistance to the insecticide used, or (d) Extradomiciliary malaria transmission has been favoured by certain aspects of human behaviour and ecology such as nomadism, outdoor sleeping, human dwellings without walls, etc. page 2 In some malarious areas of the world, difficulties of the above nature have rendered indoor spraying of available insecticides largely ineffective. The extent of such problem areas is limited but is gradually increasing, and may become much greater when large scale malaria programmes are developed in tropical Africa. The search for substitute residual insecticides is actively under way, but antilarval measures appear to offer the best potential for immediate application. DEFINITION OF ANTILARVAL OPERATIONS Antilarval operations are any measures which will prevent, reduce or eliminate the production of the aquatic stages of malaria vector species. They include: (a) Changing the environment of a breeding place to make it unsuitable for the development of mosquito larvae; (b) The use of biological agents such as larvivorous fish; (c) The conservation and efficient use of water supplies as well as the proper disposal of waste water to prevent the unnecessary creation of mosquito breeding places; (d) The use of mechanical metnods to eliminate, reduce or alter mosquito breeding places; (e) The use of chemical larvicides to kill mosquitos in their aquatic stages. THE PLACE OF ANTILARVAL OPERATIONS IN MALARIA PROG~ES To attain malaria eradication man must apply all effective methods available, and simultaneously pursue research for y~t more effective measures. The eleventh report of the Expert Committee on Malaria (WHO, 1964) (34 ) paid special attention to the increasing need for the application of additional methods of vector control in malaria eradication programmes, especially in areas where the response to residual insecticides in adult vectors is unsatisfactory, and stated that: "The present trend indicates a greater use of larval control in the near future and therefore urgent action is required". The Committee formally recommended: "That larval control be used more fully in special circumstances and that its further improvement should be studied especially in those areas that are refractory to residual spraying operations".