The Significance of thepH in the Development of Mosquito Larvae

Abstract

1. Previous work by the writer drew attention to the fact that thepH index of natural waters was in some manner correlated with the presence or absence of particular mosquito larvae.2. The observation led other investigators to study this hypothesis, and a short summary of their published records is given.3. The actual significance of thepH index was, however, obscure, and the present work has been undertaken to attempt to demonstrate the actual significance of thepH in mosquito breeding-places.4. By gradually eliminating first one and then another of the interacting factors, the writer has been able to demonstrate (a) that if thepH of the normal environment is changed the development of the larvae is adversely affected; (b) that under bacteriologically sterile conditions the foregoing statement is no longer true; and (c) that consequently the acid or alkaline reaction of the medium, within ordinary limits, has no direct effect upon the development of the larvae.5. Nevertheless, it is shown that the influence of thepH. is of unquestionable importance and that its significance lies in the fact that, under natural conditions, it indicates the favourable or unfavourable association of chemical and biological factors in the breeding-places upon which the successful or unsuccessful development of the larvae depends.6. It may therefore be stated that although thepH index is not an infallible guide, it does in the majority of instances provide a reliable index as to whether the necessary combination of chemical and biological factors in any given water are such that they will permit the development of the larvae of particular species. Some species find their optimum conditions for development in waters which are acid, others in waters which are alkaline, and it can be shown that to alter thepH of such waters is often to bring about a complete change in the biological group associations, which frequently means the acquired abnormal dominance of factors unfavourable to a particular species of larvae. Clearly, the system is to some extent elastic, and in rare instances what are in general acidophile larvae may be found in waters showing alkalinity.7. The chief conclusion is, however, that in most instances in various localities the larvae of certain species do actually show a restriction to waters exhibiting apH index within a definite short range, and that thepH index is consequently often a reliable index also as to whether the chemical and biological group associations will favour or preclude the successful development of such larvae.8. A new technique is described for the production of a high percentage of successful cultures ofAëdes argenteuslarvae and pupae under bacteriologically sterile conditions.9. The phase of “suspended development” has been investigated and is found to have its probable explanation in the temporary or complete disappearance of micro-organisms on which the conversion of the organic materials of the environment, to a suitable larval diet, depends.