﻿262 L. NIOHOLLS— SOME OBSERVATIONS ON THE BIONOMICS AND BREEDING- 

 HI. Permanent Waters. 



In these places larvae are occasionally found, usually in small numbers, and the 

 struggle for existence is such that relatively few become imagines. 



(a.) Edges of rivers and streams. The adaptability of these as breeding- 

 grounds depends upon the rate of the current and the amount of overgrowing 

 vegetation. Plate VIII, fig. 1, shows a swiftly running river which arises from 

 the hills seen in the background ; note the ripple of the strong current. Though 

 the edges are somewhat overgrown, I have never found larvae in searches 

 on 45 occasions. Near its mouth the stream becomes sluggish, and here by its 

 overgrown banks (Plate VIII, fig. 2) larvae were found five times in twelve 

 searches during dry weather ; but when, in wet weather, the river is rising 

 and falling many feet in a few days, no larvae can be found. A back-water 

 of the same river (Plate IX, fig. 1), which is never much overgrown, is a 

 favourite feeding-ground for shoals of small fish. I have never found larvae 

 here (34 searches). 



(b.) Edges of lagoons. Three lagoons have been under continuous observation. 

 Two of them team with " millions " fish, and larvae have never been found 

 (45 and 32 searches respectively). In back-waters connected with the third they 

 have been found on 17 occasions in 112 searches, though the lagoon itself is full 

 of a variety of fish and other natural enemies. 



(C.) Artificial concrete garden-tanks, rain-tanks or " taches," which always 

 contain water and are used for irrigation or agricultural purposes. When these 

 become overgrown or covered with algae they may contain numerous Anopheline 

 larvae. The number of these will vary with the nature of the surroundings ; 

 thus, if numerous Anophelines are produced in the immediate neighbourhood, 

 many larvae may be found ; the reverse is the case where there are few 

 surrounding breeding-grounds. These tanks support numbers of dragon-fly 

 larvae and consequently few Anophelines hatch out, as they and other mosquito 

 larvae furnish the chief food of these creatures in these circumstances. This is 

 demonstrated by the following experiment. 



To a tache containing six Anopheline larvae, which appeared well protected by 

 algae, 50 more larvae were added and the tache " tented " with muslin ; only 

 two mosquitos hatched out. Other experiments produced an average of 4*4 per 

 cent, adults. 



IV. Miscellaneous Collections of Water. 



From all of these Anopheles larvae are normally absent. 



(a.) In water-receptacles around houses, such as tanks, calabashes, tins, broken 

 crockery, shells of coconuts, etc., I have never found either A. argyrotarsis or 

 A. albimanus. I have records of examinations of over a thousand of these water- 

 receptacles, which are the principal breeding-places for the larvae of Stegomyia 

 and other mosquitos. 



(b.) Natural collections of water in wild pines, plantains, tannias, and holes 

 formed in the decaying trunks of trees, are situations in which Anopheles are never 

 found. 



