72 PREVENTIVE AND REMEDIAL WORK AGAINST MOSQUITOES. 

 MR. THIBAULT's OBSERVATIONS. 



In considering the normal relation between mosquitoes and fish, 

 Mr. James K. Thibault, jr., of Scott, Ark., in a recent communica- 

 tion presents some interesting views and gives an interesting instance 

 which he considers typical in some localities: 



Personally, I do not think that mosquitoes ever breed in the presence of fish if the 

 water is open, allowing the fish free access to the larvae, yet it is a matter of common 

 observation that under certain favorable circumstances some species do breed regu- 

 larly in streams where fish are abundant. Yet even where conditions are favorable 

 only a very few species seem to take advantage of it. So far as my own observations 

 go the only mosquitoes that regularly do so in this locality are Anopheles quadrimacu- 

 latus and Culex abominator. 



Conditions are favorable when the surface of the water becomes carpeted with 

 aquatic vegetation which restrains the fish in their movements yet allows ample room 

 and protection for the larvae of the above-named species. There is a certain deep, 

 slowly running bayou here that is the main breeding place for quadrimaculatus and 

 abominator at present, while two years ago not a larva could be found there at all. The 

 explanation is simple and may be given as a typical example of its kind. Two years 

 ago launches passed through this bayou daily and all logs and drift were removed as 

 soon as found so that the water had free passage and the pond weeds found no foothold, 

 except very near the banks where they were completely destroyed by stock. After 

 the launches stopped passing through this bayou logs soon accumulated and the pond- 

 weeds immediately took possession, so that throughout the present season quadrimacu- 

 latus and abominator have bred continuously and abundantly in this bayou. 



It must be noted in passing that the larvae, pupae, and freshly emerged adults bred 

 in such a location are invariably bright grassy green in color, which gives them an 

 additional advantage over the fishes. This is not the case with larvae, etc., found in 

 other places. 



DESTRUCTION OF LARViE. 



Of course the abolition of accidental breeding places, the under- 

 taking of drainage measures, and the practical use of natural enemies 

 such as fish, result in the destruction of larvae, but in this section it is 

 proposed to treat of those measures which involve the use of what 

 have come during recent years to be termed "larvicides." The dic- 

 tionary definition of the word insecticide is "one who or that which 

 kills insects, as insect powder;" therefore a definition of larvicide 

 would be one who or that which kills larvae. But in mosquito work 

 it has come to be used for those substances which are applied to bodies 

 of water in which mosquito larvae are living, and which result in 

 their destruction in one way or another. These substances, for the 

 most part, are either poisons or more frequently oils which, forming a 

 surface film, destroy the larvae when they come to the surface to 

 breathe. Ronald Ross long ago pointed out the great desideratum 

 in this direction in the following words: 



I have long wished to find an ideal poison for mosquito larvae. It should be some 

 solid substance or powder which is cheap, which dissolves very slowly, and which 

 when in weak solution destroys larvae without being capable of injuring higher ani- 



