FISHES FOR CONTROL OF MOSQUITOES. 5 



eral means of attack. By spreading a thin film of oil on the surface 

 of the water the opening of the breathing tube is clogged and the 

 mosquito, either repelled by or unable to break through the film, 

 consequently quickly succumbs to oxygen starvation. 



These methods and others that operate by changing the physical 

 environment have the disadvantage for univei-sal application that 

 they are seldom confined in their effects to the mosquito alone. The 

 complete destruction of pools or swamps, of course, destroys along 

 with the young mosquitoes all of the associated life dependent upon 

 aquatic conditions. The effects of the oil film are equally deleterious 

 to other insects having habits similar to the mosquito larvae, to the 

 surface plankton, and to many delicate, partly submerged plants 

 and even to some fishes. Other larvicides in common use are also 

 not specific in their action and may be poisonous to other organisms 

 than mosquitoes. A larvicide that will kill the young of mosquitoes 

 only is a great desideratum. 



Quite aside from the natural desire of the biologist to preserve 

 rather than to destroy life there are important reasons, chiefly pisci- 

 cultural, sanitary, or esthetic, why aquatic life should be disturbed 

 as little as possible. With the progressive contamination of our 

 larger streams the waters of swamps, ponds, and brooks are becom- 

 ing steadily more important as reservoirs from which must come 

 certain of the purifying organisms upon which to a considerable 

 degree the salubriousness of an area depends. 



More directly apparent is the viewpoint of the fisheries. The 

 very bodies of water in which mosquitoes breed so freely teem also 

 with those minute forms of life which are the primary source of 

 food supply of many insects, worms, and small fishes which again 

 form the dietary of important food and game fishes. If the supply 

 of the latter afforded by our fresh waters is to be increased, as is ob- 

 viously desirable, or even to be maintained, these reservoirs of pri- 

 mary food supply must be safeguarded. The Bureau of Fisheries is 

 greatly interested in this aspect of the problem as are the numerous 

 State commissions and societies for the promotion of the inland 

 fisheries and angling. 



There are many other reasons why ponds and marsh areas should 

 be conserved, as far as possible. The infant art of aquiculture will 

 have much need of them when in the future it comes into its own. 

 To wipe out absolutely entire ecological associations because a single 

 member of a numerous community happens to offend is unscientific 

 and clumsy and likely sooner or later to bring reprisals. Our suc- 

 cessors will condemn us as we have condemned our predecessors for 

 like delinquencies if we of to-day fail to conserve these resources. 



Societies, like individuals and species, are possessed of a great 

 capacity for self-regulation. They are plastic and within ascertain- 

 able limits will readily adjust themselves to disturbances in both 

 the delicate internal balances existing between their component mem- 

 bers and the external balances between the whole complex and its 

 external environment. How to change the status of a single mem- 

 ber of such a society clearly lies within the province of study of 

 that branch of biology now generally called ecology, which is a 

 modernized and scientific natural history characterized especially by 



