I68 MADRAS FISHERIES BULLETIN VOL. XI, 



MOST SUITABLE GROUNDS FOR MOSQUITO LARV^ AND 

 THEIR NATURAL ENEMIES. 



The places selected by malaria-carrying mosquitos for deposit- 

 ing their eggs are very numerous and vary from large swamjjs, 

 ponds, etc., down to the small collection of water in the hollow of 

 a tree or broken chatti pot. 



During Major T. S. Ross's inspections in Southern India on 

 special malarial duty he generally found the malaria-carrying 

 anophelines under the following conditions, viz. : — 



A. ciilicifacics is most ubiquitous in its selection, but generally 

 prefers clear water. 



A. barbirostris in tanks, shady pools, pot holes in rocks, 

 stagnant waters, etc. 



A. fnUiginosus in marshes, swamps, paddy fields, etc. 



A. stephensi in wells, puddles, cisterns, etc. 



A. willmori in hill streams and marshes. 



NATURAL ENEMIES. 



Where tall reeds (jambu grass) exist, not many anopheline or 

 other larvae can be found and I put this down either to the small 

 fish or to the presence of minute crustaceans. Some years ago 

 (1909) I observed some of these crustaceans {Daphnid(r-i'd.n\.) 

 attacking the eggs of a species of Yellow dun {Ephemcridcc) very 

 common in the Kurnool-Cuddapah Canal. Again when hatching 

 experiments were being carried out with the eggs and fry of 

 Ophiocephalus striatus both were attacked and destroyed by these 

 minute crustaceans. I identified the most persistent of these 

 as " Daphne pulex," and the method of attack on the fry was to 

 bite into the embryonic caudal fin and tap the caudal vein. The 

 little fish soon died from loss of blood. Mosquito larvae were intro- 

 duced into the tank and they were promptly attacked and killed. 

 The method adopted in this case appeared to consist in nipping off 

 or pulling out the long lateral hairs until the larvae were unable to 

 regain the surface and so dropped to the bottom where they were 

 seized and evidently their vital juices extracted. That they are 

 valuable larvicides is undoubted as they swarm amongst the reeds 

 of most tanks. 



The larvae and full grown beetles of the Dytiscidce are also useful 

 enemies of mosquito larvae. 



