HSHES FOR CONTROL OP MOSQUITOES. 5Y 



technique could be quickly worked out and the practicability and 

 limitations of the method determined. By what means and under 

 what conditions it can be economically applied, and how it may be 

 adjusted to the uses to which the ponds are put are questions for the 

 engineers to determine. In 'the lakes of Palisades Park these have 

 been solved, at least tentatively. In glacial and other lakes of fixed 

 IcA-el mechanical means must continue to be employed. 



A second limitation depends upon the available food supply. The 

 experiments with the common sunfish show that during periods of 

 great abundance of other food the number of mosquito larvse de- 

 stroyed decreases and the rate of residual breeding and number of 

 winged mosquitoes produced increases. There is also some evidence 

 that the same holds true of other species of fishes. To maintain a 

 maximum antimosquito efficiency of the fishes the general food supply 

 should be kept at a minimum. When the fishes are hungry they are 

 more alert and active foragers and will seek out and eat more mosqui- 

 toes than when overfed. As food supply relative to the consuming- 

 population and not the absolute food supply is the factor with which 

 we are concerned, it is clear that a pond containing a superabundance 

 of fish food is generally one insufficiently stocked with fishes. This 

 condition is therefore best remedied not directly but indirectly by 

 increasing the fish population. This reaches a higher maximum 

 when a variety of fishes rather than only one or two species are 

 introduced. Doubtless the most satisfactory conditions will result 

 in ponds stocked not only with a variety of small mosquito-eating 

 fishes but with suitable food and game fishes as well. The fry of 

 black bass, calico bass, and doubtless of other similar species will 

 eat mosquitoes and compete for the other food of the small fishes; 

 The reduction of the flora will assist by its direct influence upon the 

 insects and other animal fish food dependent upon it. 



As a third important condition for permanent stocking, care must 

 be taken to provide suitable conditions for propagation. This in- 

 cludes not only suitable places for oviposition or nesting sites but 

 means for insuring the safety and food supply of the young. Ex- 

 actly what will be required depends upon the species involved and 

 the characteristics of the body of water. In general, the welfare of 

 the fry is best secured by providing shallow refuges and shelters 

 to which they can escape and where they can find suitable food. 

 This desideratum comes somewhat into conflict witli that of re- 

 duction of plant barriers, for conditions affording shelter to fish 

 fry may also afford shelter to mosquito larvae. This is an addi- 

 tional reason for not completely destroying the shallow-water vegeta- 

 tion. Most of the larger fishes are deterred by a plant screen of a 

 density that the smaller ones and fry will pass, and the presence 

 of predacious fishes in the deeper water outside of tlie screen may 

 be expected to concentrate the mosquito-eating fishes in the very areas 

 where they will meet with the mosquito larvae. The ideal should 

 be to provide conditions that will afford the maximum concentration 

 of mosquito-eating fishes with the minimum of shelter and protec- 

 tion to breeding mosquitoes. There is little doubt that this can 

 be attained through intelligent experimentation. If a thoroughly 

 rational system of balanced aquiculture is once worked out, it is prob- 

 able that many ponds will produce fish food for human consump- 

 tion having a value exceeding the cost of establishing and main- 



