WATER BEETLES IN" RELATION TO PONDFISH CULTURE. 



233 



With our present meager knowledge outside of the Hydrophihdse it is not safe 

 to name the larvas and pupae of any species, even tentatively, by basing our judg- 

 ment on the known fauna of the pond from which the specimens were taken, on 

 their size, or on any likeness they may show to European forms. All but one of 

 the species here presented has been reared from the larva to the imago, thus making 

 its identity certain, 



LAKES VERSUS FISHPONDS. 



Attention should be called to one very pronounced difference between the 

 faima of a lake and that of an ordinary fishpond. In the former water beetles 

 are almost entirely lacking; in the latter they are one of the most abundant groups 

 present. 



Muttkowski (1918, pp. 413, 414), in discussing the fauna of Lake Mendota, said: 



With all their manifold adaptations to an aquatic life, aquatic beetles, except for a few species, 

 are scarce in the lake complex * * The Hydrobiidse, Dytiscidse, Hydrophilidse (except Berosus), 

 Donaciinae, and Gyrinidse, the latter despite the water-breathing larvse, are practically absent from the 

 lake community. The typical lake Coleoptera are the Haliplidse in the vegetation zone and the Dry- 

 opidse in the rocky and gravelly areas, while several species of adult Dytiscidse are locally abundant 

 * ^ *. The difference between the lake and other aquatic communities is very marked in late sum- 

 mer, when sheltered water, such as the lagoons in the parks and the several ponds and creeks about the 

 lake, teem with young dytiscid larvse of several species, while such larvae are conspicuously absent 

 from the lake. 



Baker (1916, p. 308), in his discussion of the relations of mollusks to fish in 

 Oneida Lake, N. Y., gave a list of the plants and animals found associated with 

 the mollusks. There were included only two species of dytiscids, one haliplid, 

 three gyrinids, and two hydrophilids. Of these, two species were found only in 

 the stomach of the painted terrapin, leaving six species for the fauna of a lake 21 

 miles long and 5.50 miles wide. 



Sherman (1913, p. 44), in summing up the habits of the Dytiscidse, said: 



In the larger bodies of water it is very difficult to locate any beetles, and in them, whether swamps, 

 ponds, or rivers, the beetles seem to occur only in very limited spots, which are usually separated from 

 the main sheet of water, such as the eddies or small pools along the shore. In fact, the small water 

 bodies are always best, and the time most favorable for collecting is when the water is low or almost 

 dried up. 



In marked contrast to this scarcity in large bodies of water is the abundance 

 of beetles in the smaller ponds. The largest of the Fairport ponds is but a trifle more 

 than an acre in area, and yet in the fauna of them aU beetles are among the most 

 numerous insects both in number of species and in individuals. Pond 5D, just 

 an acre in area, yielded 39 species, while 2E, only 0.13 of an acre, contained 31 

 species, and 12B, less than 0.02 of an acre, contained 17 species. 



METHODS. 



All the different beetle larvae that could be obtained were first studied in detail 

 until they could be easily recognized. When the larva leaves the water in order 

 to pupate, it either buries itself in the mud or constructs a pupal chamber, and on 

 transforming throws off the old larval skin. As a part of this skin the chitinous 

 I covering of the head remains entire, with the antennae and mouth parts still 



