351 



Leech and Chandler: Coleoptera 



Fig. 13:46. Helodidae, larvae, a, Prionocyphon limbatus, showing tracheal reservoirs; b, 



Elodes minuta (European sp.), to show extruded anal papillae and abdominal air bubble; c-e, 



Scirtes tibialis, first, second, and later instar larvae (a, Good, 1924; 6, Treherne, 1952; c-e, 



Kraatz, 1918). 



experiments with larvae of the European Elodes 

 minuta (1952) and of E. minuta and E. marginata 

 (1954), concluded that the anal papillae do not play 

 an important part in the respiration of the larvae 

 (neither are they of consequence in the various dip- 

 terous larvae which have them). Their chief function 

 seems to be to absorb salts in the process of stabi- 

 lizing the osmotic pressure of the haemolymph. 



The larva of E. minuta has large tracheal air sacs. 

 By contraction of the abdominal sacs it extrudes a 

 bubble from the last pair of abdominal spiracles. This 

 bubble is held in place chiefly by apical semi-hydro- 

 fuge hairs, and is in direct connection with the air in 

 the tracheal system (fig. 13:466). Treherne found that 

 larvae which had the terminal spiracles blocked to 

 prevent formation of an air bubble, and the tip of the 

 abdomen sealed to forestall protrusion of the papillae, 

 could live less than half as long when submerged in 

 well-aerated water as could untreated larvae. The 

 same result was obtained when only the spiracles 

 were plugged. Thus the terminal air bubble was the 

 important respiratory mechanism. Normal larvae were 

 found to consume about 4.50 cc. of oxygen per gram of 

 dry tissue per hour, and the bubble functioned to 

 extract oxygen from water even at relatively high 

 concentrations. It also functioned to eliminate C0 2 at 

 a greater rate than did the body surface; the papillae 

 allowed it to escape much less rapidly, but still more 

 than twice as fast as did the general body surface. 



Life history. — So little is known of the life his- 

 tories of the Nearctic species of Helodidae that it is 



unsafe to generalize. The eggs are presumably laid 

 in damp places near water; in the case of Priono- 

 cyphon this may be in water-filled tree holes. The 

 larvae are aquatic; those of only three North American 

 species have been adequately described. 



Larvae of Scirtes tibialis Gue>in were said by 

 Kraatz (1918:393) to eat the leaves of duckweed 

 (Lemna minor); but Beerbower (1944:677) found those 

 of S. orbiculatus (Fabricius) feeding on minute algae. 

 Larvae of Prionocyphon limbatus are reported to 

 eat the broken-down epidermal cells of various dead 

 leaves in ponds. The larvae of Scirtes grandis Mot- 

 schulsky of Ceylon were said by Nowrojee to be 

 predaceous, but later authors doubt this. Those of 

 S. championi Picado occur in water in the leaf axils 

 of epiphytic bromeliads in Costa Rica. 



The specialized mouth parts of Elodes hausmanni 

 Gredler (fig. lS'A7d,g), and of some other European 

 helodids have been illustrated by Beier. The man- 

 dibles with their brushes and the toothed parts of the 

 hypopharynx work with machinelike regularity, gather- 

 ing and filtering fine detritus from the surface of 

 stones and underwater vegetation. The teeth on the 

 anterior hypopharyngeal comb vary in shape and 

 number, depending on the species and genus of the 

 larva. 



Mature larvae of most genera leave the water and 

 form pupal cells in damp soil. Those of Scirtes tibialis 

 remain on the undersides of Lemna leaves; the pupa 

 is attached by its anterior end and hangs freely (fig. 

 13:47c). Walsh found the pupae of Prionocyphon dis- 



