silvery hairs on either side of ventral surface (fig. 



7:28a); western United States 



gillettei Lethierry & Severin 1896 



Ha lobates sericeus Eschscholtz 1822 

 California coast, 200 miles west (H. R. Attebery). 



Trepobates becki Drake and Harris (fig. 7:22a) 

 Colorado River, Imperial County (R. L. Usinger). 



!Key to Subspecies of Metrobates trux (Bueno) 1921 

 1. Second antennal segment pale, at least basally; apter- 

 ous forms predominantly pale; Colorado River 



subspecies trux (Bueno) 1921 



I — Second antennal segment uniformly dark; apterous 

 forms with dark markings of body predominant (fig. 



7:25i); streams of northern California 



subspecies infuscatus Usinger 1953 



REFERENCES 



DRAKE, C. J., and H. M. HARRIS 



1922. A note on the migration of certain water -striders 

 with descriptions of three new species. Ohio Jour. 

 Sci., 28:269-276. 

 1934. The Gerrinae of the Western Hemisphere. Ann. 

 Carnegie Mus., 23:179-240. 

 KUITERT, L. C. 

 o 1942. Gerrinae in the University of Kansas Collections. 

 Univ. Kansas Sci. Bull., 28, pt. 1, pp. 113-143. 

 PARSHLEY, H. M. 



1922. A note on the migration of certain water-striders. 



Bull. Brooklyn Ent. Soc, 17:136-137. 

 1929. Observations on Metrobates hesperius Uhler. I. 

 Pterygopolymorphism. Bull. Brooklyn Ent. Soc, 24:157- 

 160. 

 RILEY, C. F. C. 



1920. Migratory responses of water-striders during severe 

 droughts. Bull. Brooklyn Ent. Soc, 15:1-10. 

 TORRE-BUENO, J. R. de la 



1908. The broken hemelytra of certain Halobatinae. Ohio 

 Naturalist, 9:389-392. 

 USINGER, R. L. 



1953. Notes on the genus Metrobates in California with 

 description of a new subspecies. Pan-Pac. Ent., 

 29:178-179. 



Family VELIIDAE 



Small Water Striders, Riffle Bugs 



[Veliids, like their relatives the gerrids, have pre- 

 i apical claws and thus are able to move about without 



breaking the surface film. In general, veliids inhabit 



more protected or secluded places than gerrids, even 

 '; the marine forms (Trochopus, Halovelia, and Hus- 



seyella) occurring in the tropics within protected 

 /reefs near the shore or in mangrove swamps rather 

 I than on the open ocean. Veliids are characterized by 

 J a velvety hydrofuge pile, relatively short legs, and 



scent gland canals which extend laterally from the 



215 

 Usinger: Hemiptero 



middle of the mctastomum to the outer sides of the 

 hind acotabula, with a tuft of hairs extending outward 

 on either side and visible from above. In contrast to 

 this the Gerridae have a median scent gland opening 

 (omphalium) on the motasternum which lacks lateral 

 canals. Annectent types are discussed in terms of 

 the world-wide classification of the Veliidae by 

 China and Usinger (1949).""" 



As in the Gerridae, wing polymorphism is char 

 acteristic of all but the marine forms. Frick (1949) 

 bred alate males of Microvelia capitata Guerin in 

 Panama. He found that the percentage of alates 

 decreased in confined breeding containers but the 

 factors which determine wing dimorphism in nature 

 are not known. 



The two basic types of Veliidae in California are 

 the pond bugs of the genus Microvelia and the riffle 

 bugs of the genus Rhagovelia. Microvelias are abun- 

 dant on almost any body of standing water. They 

 abound in ponds and quiet pools of streams. Rhago- 

 velias, on the other hand, occur in large numbers in 

 the swiftest riffles of streams. They are especially 

 fitted for this habitat by virtue of a remarkable plume 

 of hairs which is inserted in a deep cleft in the tarsus 

 of the middle or swimming legs (see fig. 7:30). 



Feeding habits. — Veliids prey on almost any small 

 organisms that occur in their habitat. Frick (1949) 

 fed them through four generations on anopheline 

 mosquito larvae. 



Life history. — Bueno (1910, 1917), Hungerford 

 (1920), and Hoffmann (1925) have reared North American 

 species of Microvelia. In general, they hibernate as 

 adults. Eggs are laid singly or in clusters on floating 

 or stationary objects at the water's edge. They are 

 white and oval and are attached by a gelatinous 

 material. The incubation period is about one to three 

 weeks. Hatching is accomplished by means of a black 

 shiny "egg burster" which is shed with the postnatal 

 molt (Hungerford, 1920). Hoffmann (1925) found that 

 Microvelia borealis and M. buenoi have only four 

 nymphal instars whereas M. americana (Uhler), M. 

 hinei, and M. albonotata Champion have the normal 

 number of five. Whether or not this is constant for 

 each species remains to be seen. Frick (1949) found 

 that the normal number of instars for M. capitata 

 Guerin in Panama was five but that "Eight apterous 

 males and one apterous female had only four nymphal 

 stages," out of a total of 110 complete rearings, 76 of 

 which were apterous. The total nymphal period ranges 

 from two to five weeks in the United States. 



Distribution. — Both Microvelia and Rhagovelia are 

 world-wide in distribution. Velia is also widespread 

 but has not been found along the Pacific Coast of 

 the United States, Trochopus is the marine equivalent 

 of Rhagovelia. It occurs in the Caribbean area and in 

 Central American waters. Husseyella is known from 

 Florida and Central and South America. 



Taxonomic characters — As in other groups of water 

 striders, the male genitalia are the most distinctive 

 features of the Veliidae. However, no monograph of 

 the western American species utilizing these char- 

 acters has been attempted. Microvelia, in particular, 



