of the shell at the head end. Lethocerus eggs from 

 California measure 5.25 mm. by 2.5 mm., tapering 

 basally to 2 mm. The color is grayish to dark brown 

 with darker brown stripes at the apical end and a 

 distinct white ring marking the edges of the lid which 

 is pushed upward at hatching. The cap remains hinged 

 to the eggshell after hatching. 



The eggs of Belostoma and Abedus are glued to the 

 backs of the males and are carried in this position 

 until hatching. This is a remarkable adaptation, pre- 

 sumably serving as protection for the eggs. The 

 female may add to the batch of eggs on successive 

 days until a single male may carry more than one 

 hundred eggs. Flight is, of course, impossible during 

 ; this period, though the whole mass of eggs is readily 

 dislodged as a unit when dry. Abedus eggs have been 

 described as 5 mm. long by 1 mm. thick. They are 

 brown with a small, paler elevation at the micropylar 

 end. Harvey (1907) gives the incubation period for 

 Abedus "macronyx" as 10-12 days. Belostoma flu- 

 mineum eggs from California measure 1.78 by 0.9 mm. 



Nymphal development was found by Bueno to require 

 43 to 54 days in Belostoma flumineum Say. The ap- 

 proximate length of each of the five successive instars 

 is given by Hungerford (1920) as 4.6, 5.5, 8, 11.5, and 

 17 days. Several overlapping broods have been ob- 

 served during the year. 



Distribution. — -Belostomatidae are found in most 

 tropical and temperate regions but are lacking in the 

 northern Palaearctic region. Lethocerus is widespread, 

 but Belostoma is found exclusively in the Western 

 Hemisphere as are Abedus and Benacus. Benacus is 

 confined to the eastern United States and Abedus is 

 exclusively western, extending from California to 

 j Panama, with the exception of one species confined 

 I to Florida and Georgia. 



A specimen of Lethocerus was taken by E. S. Ross 

 in the La 3rea asphalt pits. Since the head and hind 

 tibiae are missing it cannot be placed positively to 

 species. 



Relationships,— The family Belostomatidae is quite 

 distinctive in general appearance but is usually 

 placed near the Nepidae in phylogenetic diagrams. 

 The two families have been compared on the basis of 

 terminal respiratory appendages, though the append- 

 ages are entirely different in gross appearance and 

 degree of development. The eggs of the two families 

 are entirely different and the rotatory coxae would 

 require placement in a separate "series" according 

 to one classification of the Hemiptera. The male 

 genitalia are also quite distinct so it is fair to say 

 that the family Belostomatidae has no really close 

 relatives. 



T axonomic characters. — The first monographic works 

 on Belostomatidae were by Mayr early in 1863 and 

 Dufour late in 1863. Excellent though these works 

 were, they were the source of much subsequent con- 

 fusion because of insufficient knowledge of the limits 

 of variation of North American species. De Carlo 

 (1938) produced a modern revision, but this and his 

 more recent work on Abedus (1948) suffer from lack 

 of knowledge of the limits of variation of North Ameri- 

 can species. Hidalgo (1935) also revised Abedus on 



205 

 Usinger: Hemiptera 



the basis of the large collections al the University of 

 Kansas, and Cummings (1988) straightened out the 



taxonomy of the giant water bugs of the genera Letho- 

 cerus and Benacus. The present keys are b 

 largely on the above quoted works with new character 

 introduced for separating the genera in nymphal 

 and vvith corrections in synonym) and distributional 

 records based on study of lonis, series of California 

 species. 



Generic characters as indicated in the keys are 

 reasonably adequate and distinctive, though diffi- 

 culties are encountered when Neotropical forms are 

 considered. Specific characters are much less dis- 

 tinctive — so much so that existing keys have proved 

 difficult to use in identifying our species of Abedus 

 and Belostoma. 



In Abedus the number of antennal segments (three 

 or four) and the shape of the prolongations of the 

 second and third segments have been found to vary 

 [Hidalgo, 1935, and Hussey, in litt., Abedus signoreti 

 Mayr and Abedus immaculatus (Say)]. Size (31 to 

 35 mm.) likewise appears to be of doubtful signif- 

 icance. Nevertheless, a kej is given, based on the 

 most recent revisions of Hidalgo (1935) and Do Carlo 

 (1948). A. mayri De Carlo appears to fall within the 

 range of variation of hungerfordi so it is reduced to 

 synonymy. Abedus dilatatus Say was recorded from 

 California, but I know it only from Utah and Mexico. 



Two species of Lethocerus are recognized from 

 California. Kirkaldy and Bueno (1908) record annulipes 

 (H. S.) from the state, but I have not seen specimens 

 of this. 



Fig. 7:17. Lethocerus americanus (Leidy), Oakland Hills, 

 Alameda Co., Calif., Feb. 22, 1927 (R. L. Usinger). 



