FISHES FOR CONTROL OF MOSQUITOES. 53 



numerical point is the practical problem of natural mosquito control, 

 but it is obvious that the sunfishes may be utilized in effecting it. 



Little more than this can be said for any species of fish that has 

 been used in mosquito-control work. Both Fundulus heterocUtus and 

 Gamhusla aflnh^ the value of which is now acknowledged by practical 

 antimosquito workers, are subject to similar limiting conditions, 

 though not in exactly the same combinations or degrees. The recogni- 

 tion of this fact in the case of Fundulus is the fundamental principle 

 underlying the practical method used in controlling the salt-marsh 

 mosquitoes, and Hildebrand (1919) has recentlj^ laid great stress upon 

 the importance of plant growths in limiting the effectiveness of Gam- 

 busia. The author was much impressed with this fact during a visit 

 of inspection of some of the antimalaria work in the South during the 

 summer of 1918. It was very rarely that some Anopheles larvae could 

 not be found in bodies of water occupied by Gambusia. It is also 

 probable that the factor of food supply operates with this species 

 much as with the sunfish. The author has in mind particularly a 

 small pond situated near the village of Hamburg, S. C, which 

 swarmed with Gambusia and in which large numbers of Anopheles 

 larvse of all stages could be seen easil}^ not only sheltered in Con- 

 fervse pads and among debris, leaves, etc., but also to some extent 

 floating in open spaces apparently in full view of the Gambusia. In 

 this pond were great numbers of entomostracans, naidiform annelids, 

 and various small insect larvse. The Gambusia reacted toward the 

 mosquito larvfe exactly as sunfishes do when overfed, and doubtless 

 they were in the same state of satiation. 



In addition to the nine species of fishes treated above there is reason 

 to believe that several others may have a supplementary or under spe- 

 cial conditions even a primary value in mosquito control. Several of 

 the minnows (Notropis) belong in this category. Like young roach, 

 Notropis chahjha&us and N. Ijifrenatus were observed to snap up mos- 

 quito larvce with great eagerness when fed to them in the waters in 

 which they lived under entirely natural conditions. Some experi- 

 ments with these planned for the summer of 1920 had to be aban- 

 doned. A most unexpected observation was the presence of Culex 

 larvse in the stomachs of several of the swarming young of the yellow 

 catfish {Ameiurus nehulosus) . The stickleback is another species 

 worthy of investigation. About the shores of Carnegie Lake at 

 Princeton, N. J., there appears to be a close negative correlation be- 

 tween this species and the presence of mosquito larvae, including 

 Anopheles. The young of the smallmouth black bass were observed 

 on one occasion in Little Long Pond, Palisades Park, to feed eagerly 

 on Culex pipiens larva when a boat half filled Avith water containing 

 large numbers of them was emptied. 



SOME GENERAL CONCLUSIONS AND CONSIDERATIONS BEARING 

 UPON THE USE OF FISHES TO COMBAT MOSQUITOES. 



In the preceding section there was presented considerable evidence 

 that small fishes exert a powerful repressive influence upon the 

 emergence of mosquitoes from fresh waters. This applies particu- 

 larly to ponds, lakes, and sluggish streams under natural condi- 

 tions. The relatively small numl^ers of mosquitoes produced by such 



