WATER BEETLES IN RELATION TO PONDFISH CULTURE, WITH LIFE HISTORIES OF THOSE FOUND. IN FISHPONDS AT FAIRPORT, IOWA. By CHARLES BRANCH WILSON, Ph. D. State Normal School, Department ofScience, WesVield, Mass. Contribution from the U. S. Fisheries Biological Station, Fairport, Iowa• .:I­ CONTENTS. Page. Page. Introduction . 232 Enemies of adults . 247 Importance of water beetles . 232 Turtles . 247 Ignorance of Americanspecies . 232 Birds '" .......•. 247 Lakes versus fishponds...........•.... 233 Toads and frogs ". 248 Methods..•.......................... 233 Electric lights . 248 Ecology .. 235 Beetlesas fish eaters . 249 Modifications of structure and vestiture. 235 Fish as beetle eaters .. 252 Locomotion .. 235 Evidence from fish bait.......•....... 252 Migration from one pond to another . 237 Evidence from fish stomachs•.......... 253 Distribution according to size . 238 General summary and suggestions . 260 . Structural adaptations :. 238 Beetledistributionin Fairportfishponds . 263 For locomotion . 238 Source of material.. 264 Forrespiration . 239 Influence of environment . 264 For flotation . 241 Restriction ofBpecies . 266 For sex functions '" ." . 242 Relative importance of species . 267 For sight . 242 Systematicdescription of Fairportspecies . 267 Enemies of larvse " . 242 Key for identification of larvre . 268 The larva . 242 Key foridentification of pupse . 269 Time of pupation . 243 Peltodytes __ . 271 Dragonfly nymphs . 243 P. edentulus . 271 Mites . 244 Haliplus . 273 Hydra . 244 H. ruficollis . 274 Ants . 244 Coptotomus . 275 Turtles . 244 C. interrogatus . 275 Frogs . 244 Cybister . 277 Snails . 245 C. fimbriolatus. : , 277 Parasites . 245 Dytiscus '" . 282 Enemies of pupre . 245 D. verticalis ; . 282 Water . 245 Hydroporus ,. 285 Imperfect pupation . 246 H. niger ,. 285 Parasites . 246 Laccophilus . 286 The black horsefly . 246 L. maculosus .. 286 Ants . 247 L. proximus.........•............ 290 231 232 BULLETIN OF THE BUREAU OF FISHERIES. Systematic description of Fairport species­ Systematic description of Fairport species­ Continued. Page. Continued. Page. Thermonectes . 291 Laccobius . 315 T. basilaris ~ . 291 L. agilis . 315 T. ornaticollis . 296 Enochrus . 316 Acilius . 299 E. nebulosus '" . 318 A. semisulcatus . 299 E. diffusis : . 320 Dineutes . 302 E. perplexus . 321 D. americanus . 302 Tropisternus . 321 Gyrinus . 308 T. lateralis __ . 321 G. ventralis . 308 T. glaber . 326 G. limbatus . 308 T. mixtus - . 329 Berosus . 309 Hydrous . 332 B. striatus _._ . 309 H. triangularis . 332 B. pantherinus , 311 ,Donacia . 332 B. peregrinus . 312 D. requalis ,. 332 Hydrophilus . 314 Cap attachment on egg case . 332 H. obtusatus . 314 Bibliography . 334 INTRODUCTION. IMPORTANCE OF WATER BEETLES. The beetles are far more numerous than any other order of insects and are very cosmopolitan in their distribution. Every natural pond, river, and stream is peopled with them, and if one constructs an artificial fishpond in all probability beetles will constitute its first and most permanent insect inhabitants. Pondfish culture, therefore, in order to prove successful, demands sufficient acquaintance with the water beetles to yield a workable knowledge of their economic relations to the fish. The following paper is a beginning toward such an acquaintance and endeavors to suggest lines of research that may prove both interesting and profit­ able to the fish-culturist. IGNORANCE OF AMERICAN SPECIES. Unfortunately, while our American water beetles are fairly well known to the systematist, so that they appear in museum collections and lists of species, very little is known about their life histories, their habits, and their economic impor­ tance. According to Comstock (1912), at least 300 species of carnivorous diving beetles (Dytiscidee) occur in this country, 40 species of whirligig beetles (Gyrinidss), and 150 species of water scavenger beetles (Hydrophilidee). Moreover, there are 25 species of herbivorous water beetles (Haliplidse), a family only briefly mentioned by Comstock. Out of this total of more than 500 species, which is probably far below the actual number, the habits and complete life histories of only about 20 are known. The partial development of 15 other species has been recorded, chiefly the egg cases and newly hatched larvee of hydrophilids by Richmond (1920). This excellent paper-also gave valuable keys for the identification of the egg cases, larvai, and pupee of the Hydrophilidse, but nothing of the sort has been published for the other families. Abstracts of one or two of these published life histories, which are important' from the standpoint of fish culture, are included in the present paper, and in addi­ tion those of 20 other common species are presented, together with the economic relations of the entire group. WATER BEETLES IN RELATION TO PONDFISH CULTURE. 233 With our present meager knowledge outside of the Hydrophilidee it is not safe to name the larvee and pupre 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 fauna 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 thelake complex * * *. The Hydrobiidre, Dytiscidre, Hydrophilidre (except Berosus), Donaciinse, and Gyrinidre, the latter despite the water-breathing Iarvte, are practically absent from the lake community. The typical lake Coleoptora are the Haliplidm in the vegetation zone and the Dry­ opidse in the rocky and graeelly areas, while several species of adult Dytiscidre 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 larvee of several species, while such Iarvre 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 Dytiscidre, 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 all 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 Iarvee 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 covering of the head remains entire, with the antennes and mouth parts still 234 BULLETIN OF THE BUREAU OF FISHERIES. attached, and the species can be recognized as easily from these discarded skins as from the living larves. Then a search for as many pupre as could be found was made along the shores of the ponds, and in every instance care was taken to secure the old larval skin from the inside of the pupal chamber. In this way the larvse and pupre were defi­ nitely related, one to the other, and the pupre were then kept in suitable terraria until the adult beetle emerged. On transforming from the pupa to the adult the old pupa skin is thrown off and may be obtained from the pupal chamber and used to identify the species. One of the best methods with the larger species, when a pupal chamber is found on a pond shore, is to leave it as nearly intact as possible. By cutting around it with a knife blade a small cube of earth containing the chamber may be removed. This cube can then be kept in a terrarium until the adult beetle emerges, and the chamber will contain both the larval and pupal skins. If the chamber has been opened during the removal, it should be covered again with a pellet of mud before being placed in the terrarium. Darkness is necessary for the best success in rearing the specimens. In the case of the smaller species, and often with the larger ones, the natural pupal chamber is destroyed when the pupa is found. In such cases they will thrive equally well in an artificial chamber, made as nearly the size and shape of the original as possible, and with a removable cover, so that the development of the pupa may be watched from day to day.