350 



Leech and Chandler: Coleoptera 



Fig. 13:45. Eurystethidae, Eurystethes cal ifornica. a, ventral view 

 of larva; b, pupa, ventral (Wickham, 1904). 



Key to the California Species of Eurystethes 



1. Elytra striate; head, thorax, and elytra shining, metallio; 

 Mendocino County, south at least to Farallon Islands, 



San Francisco County fuschsii (Horn) 1893 



— Elytra not striate; head, thorax, and elytra alutaceouS 

 and subopaque; Marin County, south to San Mateo 

 County subopacus Van Dyke 1918 



REFERENCES 



BLACKVVELDER, R. E. 



1945. Checklist of the Coleopterous insects of Mexico, 

 Central America, the West Indies, and South America. 

 U.S. Nat. Mus., Bull. 185: 343-550. 

 CROWSON.R. A. 



1953. The classification of the families of British 

 Coleoptera (continued). Ent. Mon. Mag., 89:49-59. 

 HORN, G. H. 



1893. Miscellaneous Coleopterous studies. Trans. Amer. 

 Ent. Soc., 20:136-144, 1 pi. 

 VANDYKE, E. C. 



1918. New Inter-tidal rock-dwelling Coleoptera from 

 California. Ent. News, 29:303-308. 

 WICKHAM, H. F. 



1904. The metamorphosis of Aegialites. Canad. Ent., 

 36:57-60, pi. 2. 



Family HELODIDAE 



a few are bicolored. The larvae are associated with 

 water or very damp places. 



The adults are never strictly aquatic, but those of 

 some species unhesitatingly enter the water to escape 

 from danger. Adults of certain genera, such as Scirtes, 

 occur on foliage near the larval habitat, but are not 

 known to enter the water; some, including species of 

 Cyphon, may be taken on flowers. 



Only three genera, Elodes, Cyphon, and Scirtes 

 have been reported from California, but Prionocyphon 

 has been found in western Arizona. 



Relationships. — The family Helodidae belongs in 

 the superfamily Dascilloidea, and has often been 

 included as but a division or group within the Dascil- 

 lidae. On the other hand, even in some fairly recent 

 works the Eucinetidae, and Eubria of the Psephenidae, 

 have been treated as subfamilies of Helodidae. 



The rather Lepisma-like larvae are at once known 

 by their long, multiarticulat antennae (fig. 13:46c-e). 

 Such antennae are not found in any other larval Cole- 

 optera, nor indeed, according to Crowson, in the 

 larvae of any other holometabolous insects. However, 

 Kraatz (1918) has shown that the first and second 

 instar larvae of Scirtes tibialis Gue>in have fewer 

 antennal segments (fig. 13'AQc,d), and Peyerimhoff 

 (1913) said that those of the European Prionocyphon 

 serricornis Miiller changed into short and more typi- 

 cally coleopterous antennae when the larvae were 

 exposed to dry environments. 



Respiration. — Adults are not known to stay under 

 water for long at a time, and presumably rely on what 

 air they carry down under their elytra. By means of 

 simple experiments with nitrogen-saturated and with 

 oxygen-saturated water, Popham (1954) has shown 

 that the air bubbles and/or film carried down by 

 aquatic insects do function also as physical gills. 

 To benefit the insects these air supplies, exposed 

 to the water, must be connected to the tracheal sys- 

 tem. For most species it remains to be found what 

 percentage of the total oxygen requirement is supplied 

 in this manner; the temperature of the environment 

 and activity of the insect are major factors in the 

 appraisal. 



The spiracles of the larvae are vestigial or absent, 

 except for an annuliform pair on the eighth abdominal 

 segment. The larvae have to come to the surface 

 periodically to replenish their air supply (fig. 13:48<z). 

 At least some species have very large tracheal res- 

 ervoirs; those of Prionocyphon limbatus have been 

 illustrated by Good (fig. 13:46a). In addition, the 

 larvae have terminal retractile gills 13 (fig. 13:47a, b) 

 with which they have been presumed to extract some 

 oxygen from the water. 



Benjamin Walsh (in Osten Sacken, 1862:117) stated 

 that submerged larvae of P. discoideus extruded the 

 gills "vibrating [them] vigorously up and down . . ." 

 Such action suggests that the gills may be of con- 

 siderable use as such, but Treherne, in controlled 



This family has a world-wide distribution. The North "It is remarkable that of the two Nearctic species of Priono- 



\r.^rw.r,„ Li„,i;,i „_„ ,,™„ll „„ o( i„ o ~- a .v, ™ ;„ cyphon, the larvae of P. discoideus (Say) have three prominent 



American nelodias are small, mostly 6 or 4 mm. in ' v , ' , . . . .,, /r . 10 An \ , ., r , p 



. ., . ,. ' .. J , .. tassels of bipectinate gills (fig. 13:47a), whereas those of r. 



length and rarely exceeding 6 mm. Many of the species limbatus LeConte have five fingerlike gills resembling those of 



are yellowish-brown, some are rufous, some black, and figure 13:476. 



