WATER BEETLES IN RELATION TO PONDFISH CULTURE. 



261 



others that are eminently desirable. Even if it were possible to eliminate these 

 three species they are themselves good food for older fish and are as freely eaten 

 as any of the other species, so that it would seem to be poor economy to kill them off. 



Again any attempt to eliminate the obnoxious beetles must employ mechanical 

 means since chemicals are out of the question. This being true it will be found 

 difficult to get rid of the beetles without sacrificing the other kinds of insect larvae 

 which can not consistently be spared since they furnish the very food upon which 

 the young fish most depend. 



Trap lanterns set at night around the shores of the fishpond will capture many 

 of the adult beetles. The larger species are the ones most accustomed to flying 

 at night and they are easily attracted by a bright light. If this mode of attack 

 is started by the middle or last of May, before the beetles begin to breed, and is 

 consistently followed, it will destroy large numbers of the very species that are 

 most obnoxious. However, this is a preventive measure, to be applied beforehand, 

 and not a cure after the infection has appeared. It is tedious, involves consider- 

 able expense, and has no effect upon the larvae but only upon the adults. What 

 the fish-culturist really wants is a remedy that may be applied with sufficient 

 celerity to save the remainder of the hatch when once the beetles have begun their 

 ravages, since ordinarily there is no necessity for preventive measures. 



The use of a dip net in the shallow waters around the shores of the pond, pushing 

 the net towards the the shore and to the very water's edge, will capture many of 

 the larger larvae and adults. If persistently followed, it will materially reduce the 

 numbers of the obnoxious species and might check their ravages sufficiently; but 

 it is a slow and very laborious method at the best and does not appeal to the average 

 fish-culturist as possessing the requisite celerity. 



The only method of removing the beetles quickly and thoroughly is by drain- 

 ing the fishpond. If the fry can be kept an hour or two in a large tank after the pond 

 has been nearly drained, the draining may then be fully completed. The large 

 beetle larvae and adults thus become conspicuous, traveling around in search of 

 water, and practically every one of them may be captured. Witness the draining 

 of one of the Fairport fishponds as related on page 250. The fish may then be 

 returned with safety to the pond as it is refilled. This method has certain disad- 

 vantages noted below, and it will also be necessary after the larvae have been de- 

 stroyed to make sure that a second brood does not appear. There may be many 

 pupae in chambers around the edge of the pond which would emerge as adults if 

 left alone. They may be destroyed by raising the pond level 8 to 12 inches, keeping 

 it up for half a day and then lowering it again. If this were done once a week during 

 the summer, it would mean that no beetle larvae could develop into the adult stage, 

 since they would all be drowned while in the pupal chamber (see p. 245). Such 

 universal destruction is not at all desirable, but it indicates the effectiveness of the 

 remedy. Any of these methods of getting rid of the beetles is only to be used in 

 emergencies as a sort of last resort. The second method mentioned above, that 

 of removing the fish fry to another pond, is much to be preferred and is worthy of 

 separate discussion. 



5. If a second pond is available, transferring the fry to it will effectively rid them 

 of their enemies. The original pond can then be stocked with larger fish that will 

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