262 



BUULETIN OF THE BUKEAU OF FISHERIES. 



use the beetles for food. Of course, in making such a transference care must be 

 taken that the same species of beetles are not present in the second pond. This will 

 almost never happen, however, even when the two ponds are close together and to 

 all appearances the conditions are the same. During the summer of 1920 the only 

 fishpond at Fairport in which any Cybister larvaB were found was pond 5D. Adults 

 were found in several adjacent ponds but no larvae. Similarly, Hydrous larvae 

 were confined to ponds 3E, 4E, and 14B, and nothing but straggling individuals 

 appeared elsewhere. Dytiscus adults were fairly common in ponds 2, 3, 4, and 8, 

 in series D, and in 16B, but not a single larva was captured during the entire sum- 

 mer in any pond. The larvae of Thermonectes ornaticollis were confined to pond 12B, 

 and none were found in any other pond, although the.^dults were common enough. 

 In 1921 the large dytiscid larvae described on page ^84, which were probably those 

 of Acilius semisulcatm, were found only in pond 7D; none could be found in ponds 

 5, 6, or 8, all of which are very close to pond 7. The buffalofish fry taken out of 

 pond 3E (see p. 250) in July, 1918, were carried only a short distance to another pond 

 in the same series, but there they were entirely free from attacks of beetle larvae. 

 Such a transference of the fish fry, therefore, is the simplest, the most reasonable, 

 the quickest and the most effective method of freeing them from the attacks of beetles. 

 It must be borne in mind, however, that in draining a pond either for the destruc- 

 tion of the obnoxious beetles or for the transference of the fish fry these latter are 

 always subject to increased depredation by the beetles during the operation. The 

 lowering of the water brings the larvae and fish fry together in a steadily diminishing 

 area. The beetles are almost certain to take advantage of this opportunity and 

 kiU many of the fry; but the danger is only temporary, and as it can not be avoided 

 it must be accepted as one of the means necessary to the ultimate deliverance of 

 the fish from their enemies. As in all warfare some sacrifice is necessary in order 

 to secure final victory. 



6. There is also another method that merits at least some attention, namely, 

 the wintering out of a breeding pond. If a pond is drained in the fall and left dry 

 through the winter, all the insect larvae it contains, including any beetle larvae 

 that might possibly remain, will be destroyed. The adults will migrate elsewhere 

 or will be killed, and in the spring the pond will be clean and free from all obnox- 

 ious pests. If a pond were persistently infested with any insect enemies of young 

 fish, it might be advisable to winter it out. The chances of reinfection during 

 the following year will thereby be greatly diminished, and in the majority of cases 

 it will remain free from the pests for several years. Here again, however, it must 

 be remembered that such a procedure gets rid of all the insect fauna, the beneficial 

 as well as the harmful. Consequently, there will not be as much fish food the 

 following year, and the fry will be compelled to depend upon whatever happens 

 to get into the pond unless they are fed artificially. If the latter method be adopted, 

 or if the pond be filled with water pumped from a river or lake, there will probably 

 be plenty of food for the fry. In such cases the wintering out of a fishpond is 

 one of the most effective methods that can be adopted for getting rid of obnoxious 

 insects. On the contrary, if the pond be fed from springs, some provision must 

 be made for a food supply the following year. 



