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, pus hing 
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 dra ining 
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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