The Larval Habitats of Aedes Polynesiensis Marks in Tahiti and Methods of Control

Abstract

Discussion and Summary A program of control directed against Aedes polynesiensis is not easily achieved because the locations where the larvae are to be found are so diversified. Consequently, one must direct attention not to a single habitat but to all receptacles that hold rain water. As a guide to the control, one is tempted to make an evaluation of the containers in which breeding is found and place them in ranks in order of their importance. Although such a list has value in demonstrating the variety of habitats in which the larvae of Aedes polynesiensis may be found, the relative importance of each will vary from area to area. The importance or rank will depend upon relative abundance, volume, permanence, proximity to habitations or places of work or play, rainfall and suitability for breeding. A somewhat more useful listing is to enumerate all types of containers capable of holding water (potential breeding containers). This is a census of the relative abundance of all types, breeding or not. A second listing giving the number of these containers with larvae of Aedes polynesiensis (actual breeding containers) enables one to determine the percentage of each available type in which breeding is actually occurring. Thus one determines the type of container where breeding is found most commonly. Jachowski (1954) has given a tabulation for Aedes polynesiensis in Samoa and the usefulness of this type of survey in Aedes control in Hawaii has been reported by Bonnet (1947). These lists will have little value unless the sample is quite large and obtained during 1 or 2 years. This requires careful, systematic, continuous inspection of all areas on a cycle related to the length of time from egg to adult mosquitoes and can rarely be carried out because of the high cost of intensive inspections. Further, it is obvious that such lists must be interpreted with care since no allowance is made for differences in quantitative production of mosquitoes from each container. A medium sized tree hole where the environment for the mosquito larvae is excellent for an entire year, may produce many more mosquitoes than several hundred rat-eaten coconuts. The latter may produce during only a few months of the year and then only during the period the contained water is not polluted. Yet small rock holes, by their very numbers, individually producing very few mosquitoes, may produce more than the tree holes when the production is summated. This continuous production of mosquitoes is particularly important in the problem of filariasis transmission since filariasis requires frequent reinfection in order to maintain the disease in the human host (cf. Jachowski, et al., 1951, 1952). A large error may also be introduced if one overlooks the presence of eggs resistant to desiccation. One may have the impression from a survey that only a small percentage of rock holes, tree holes or crab holes are producing adult mosquitoes when, after a rainfall, 100 per cent or nearly so will have larvae which have hatched from the ever-present eggs. At the present time, control of Aedes polynesiensis is dependent upon inspection of inhabited areas with the discovery and elimination of all waterholding containers. As an aid to the finding of the containers the cutting of brush and weeds for a distance of not less than 100 m from houses is recommended. Temporary containers such as bottles, tin cans, coconut shells, rat-eaten coconuts, and miscellaneous junk must be stored in dry places until destroyed by burial or dumping in the sea. Canoes should have rain water drained out regularly. Certain permanent useful containers such as cisterns, troughs, animal drinking pans, and ant guards cannot be eliminated and methods must be devised to make them unsuitable for mosquito breeding without destroying or interfering with their useful function. It is believed that the most important sources of Aedes polynesiensis in Tahiti are the permanent, natural, breeding containers including tree holes, rock holes and crab holes. These containers serve to maintain mosquito populations through dry periods and act as “mother foci” to inoculate the temporary containers which cease to produce mosquitoes during adverse weather conditions. Although the elimination of all containers which can breed Aedes polynesiensis is the ideal and should be attempted, it is not always possible to carry this out for practical reasons. A concentrated attack upon the permanent, natural, breeding containers should produce a greater degree of reduction per expended man-hour and therefore be less costly. This review of the breeding locations of Aedes polynesiensis has been presented to emphasize some of the problems and difficulties encountered in the control of this medically important mosquito. It can be controlled, and its population reduced, if the persons engaged in the program not only use their imagination in finding the location of the larvae but also devise and enforce permanent methods of elimination or control.