294 



Leech and Chandler: Coleoptera 



tocene (7) and Miocene (1). Several of the Pleistocene 

 dytiscids and hydrophids are from the La Brea, Cali- 

 fornia, tar pits, and have been identified as species 

 still living in the region. 



Economic importance. —A few species of water 

 beetles, both larvae and adults, are actually pests of 

 cultivated plants (the rice weevils, Lissorhoptrus 

 spp.; Kuschel, 1951), or occasionally attack field 

 crops (Helophorus spp. on turnips, cabbages, swedes, 

 and other crucifers). Adults are sometimes troublesome 

 in domestic water supplies (Hurst, 1945); larvae of 

 the larger dytiscids (Dytiscus, Cybister), hydrophilids 

 (llydrophilus), and perhaps gyrinids (Dineutus), may 

 kill small fish in rearing ponds and presumably in 

 nature (Wilson, 1923); others may attack tadpoles 

 (Williams, 1936). Some species are the secondary 

 hosts of trematodes (see section under Parasites). 

 Adults of the Dryopidae, and both adults and larvae of 

 the Elmidae, Chrysomelidae, and Curculionidae feed 

 on the roots and other parts of aquatic plants, but the 

 total damage they do has never been assessed. 



These bad features are offset by the uses to which 

 water beetles are put. Predaceous species of the 

 terrestrial hydrophilid genus Dactylo sternum have 

 been used in control programs against the sugar-cane 

 beetle borer in the Philippine and Hawaiian islands, 

 and against the banana borer in Jamaica. Both adults 

 and larvae of the Haliplidae, Dytiscidae, and Hydro- 

 philidae (Martin and Uhler, 1939) comprise a regular, 

 and sometimes major part of the food of aquatic birds, 

 as well as of turtles, frogs, toads, salamanders, and 

 fish (Wilson, 1923). Many water beetles fly well, and 

 during the spring and fall dispersal flights there are 

 tremendous numbers in the air, especially during the 

 afternoon and evening; birds and bats must eat num- 

 bers of them. In various parts of China large dytiscids, 

 Cybister spp., and hydrophilids, Hydrophilus spp., are 

 commonly eaten by humans, both as medicine and as 

 confection (Hoffmann, 1947; Bodenheimer, 1951). On 

 the other hand water beetles are suitable as aquarium 

 animals (Lutz, 1930; Boardman, 1939). In addition, 

 certain aquatic beetles have proved to be good sub- 

 jects for research in physiology (Hodgson, 1953). 



Parasites. — Most parasites of water beetles are of 

 academic interest only, but further research may prove 

 some to be of more importance than suspected. Pujatti 

 (1953) reported the metacercaria of a trematode of 

 the genus Lecithodendrium, whose primary host was 

 thought to be a bat, from both dytiscids (Hydaticus, 

 Cybister) and hydrophilids (Hydrophilus, Neohydro- 

 philus), from Bangalore, Mysore, India. Hall (1929) 

 listed the European dytiscid Ilybius fuliginosus as the 

 secondary host of Haplometra cylindracea, a trematode 

 of frogs, and Dytiscus marginalis as containing the 

 cercaria of a trematode. Since water beetles are eaten 

 by fish, reptiles, amphibians, birds, and some mam- 

 mals, it will be surprising if they do not prove to be 

 involved in the life cycles of other trematodes, as 

 well as of cestodes, nematodes, and acanthocephalids. 

 (For references to nematodes in water beetles, see 

 Todd, 1942, 1944; La Rivers, 1949; Jackson, 1951). 



It is not uncommon to find red or reddish-brown 

 egglike things attached to the dorsum of the abdomen 



of water beetles, under the elytra and wings, and 

 occasionally on the legs or ventral surface. These are 

 immature water mites (Hydracarina), which may occur 

 in several stages, some being active, others sessile. 

 They actually suck the blood of their hosts. 



Tiny proctotrupid and chalcid wasps parasitize the 

 eggs of Dytiscidae, and larger wasps parasitize the 

 pupae of Gyrinidae (q.v.). Many small dytiscids and 

 hydrophilids, especially species of Hydroporus, ma\ 

 be so heavily coated on the undersurface by Proto- 

 phyta and Protozoa that parts are obscured. Protozoan 

 parasites occur in the digestive tracts of some water 

 beetles. 



A very interesting order of ascomycete fungi, the 

 Laboulbeniales, occurs on insects. Despite the clas- 

 sical series of monographs by Thaxter (1896-1931), 

 knowledge of the species on water beetles is prelim- 

 inary. R. K. Benjamin writes (1952): "The Laboul- 

 beniales are a large and diverse order of very small 

 Ascomycetes which are known to develop only upon 

 the chitinous integument of living insects and, more 

 rarely, of mites (arachnids). Thaxter (1896, 1908, 

 1924, 1926, 1931), who studied the Laboulbeniales 

 more extensively than any other student, frequently 

 observed that certain species exhibit a remarkable 

 tendency to grow on very restricted portions of the 

 host integument. Such specificity of position may be 

 characteristic only of certain isolated species or may 

 be a regularly occurring phenomenon within a given 

 genus. In the genus Chitonomyces Thaxter which 

 infests aquatic beetles belonging to the families 

 Dytiscidae, Gyrinidae, and Haliplidae, for example, 

 most species, especially those occurring on Gyrinidae, 

 Haliplidae, and the Dytiscid tribe Laccophilini, are 

 so restricted to definite areas of the host surface 

 that identification of the parasites, when the host is 

 known, can be made with remarkable accuracy bj 

 noting merely their position upon the integument. 

 Frequently one insect species is subject to infection 

 by a number of different species of Laboulbeniales, 

 often representing several genera. Outstanding exam- 

 ples of multiple infection coupled with position 

 specificity are the parasites of Orectogyrus specularis 

 Aube (Gyrinidae) and Laccophilus maculosus Germ. 

 (Dytiscidae). Orectogyrus specularis is known to be 

 infested by no fewer than sixteen species of Chito- 

 nomyces (Thaxter, 1926, p. 511-512), all of which 

 are found on certain very restricted areas of the 

 terminal abdominal segment and the neighboring 

 genital lobes. As many as ten of these species of 

 Chitonomyces have been found growing on the same 

 host individual. Laccophilus maculosus is parasitized 

 by at least twelve known species of Chitonomyces 

 which are all very specific for their point of attach- 

 ment to the host." 



Dr. Benjamin has been so kind as to provide the 

 following list of genera attacking water beetles (based 

 on the world fauna): 



Haliplidae — Chitonomyces; Hydraeomyces. 



Dytiscidae — Chitonomyces. 



Gyrinidae — Laboulbenia. 



Hydrophilidae — Autoicomyces (on Berosus); Cera- 

 tomyces (on Tropisternus, Hydrochus); Rhyncho- 



