Mosquito Breeding and Malaria in relation to the Nitrogen Cycle

Extract

Many anti-malarial workers have recorded the larval habitats of Anopheline species, and while their records usually reveal a variety of types of breeding-places for the same species even in one and the same country, the characterisation of the breeding waters usually lacks precision. This is hardly surprising, since descriptions are based upon naked eye observations, and only physical aspects of the breeding-places, or in addition only the most striking characteristics of the associated forms of vegetation are recorded, more or less casual information being given concerning the depth, clear or muddy character, and stagnation or currency, of the water, together with even more incomplete statements relating to the plants growing in or near it. The statement, not unimportant in itself, is, for example, often volunteered that larvae of a particular species are found in streams or pools with grassy margins, while information is usually lacking relating to the species of even the more conspicuous plants which grow in the water itself, and which are characteristic of it or of the presence of particular Anopheline larvae. For example, it has been found that in Malaya in ricefields on the flat coastal plain, the presence of the floating plant Utricularia flexuosa is widely associated with larval associations in which Anopheles sinensis predominates over A. barbirostris, other Anophelines being generally absent (Williamson, 1925). It seldom if ever happens, however, that an aquatic plant has the same range of adaptability as the associated mosquitos. For example, in the case quoted, U. flexuosa abounds over many square miles in the Krian rice-fields, from which all Anopheline larvae are absent, despite the proximity of their breeding-grounds; and conversely, A. sinensis and A. barbirostris are very commonly found unassociated with Utricularia.