190 



Usinger: Hemiptera 



Artemia salina, and the brine fly, Ephydra gracilis. 

 The bugs also occur in the saline waters of former 

 lake beds in the California deserts. They are the 

 dominant insect of the extensive inland Salton Sea 

 and thrive at Badwater in Death Valley. 



Corisella decolor and C. inscripta likewise show 

 a preference, or at least a tolerance, for saline waters. 

 Although absent from the situations described for 

 Trichocorixa, they occur in enormous numbers in 

 Little Borax Lake, near Clear Lake, and in the septic 

 waters of the sewage oxidation ponds at Concord, 

 Contra Costa County. 



It is interesting to note that both Trichocorixa and 

 Corisella are commonly found in pairs, two closely 

 related but perfectly distinct species living together 

 under what appear to be identical conditions. 



The remaining genera of California corixids com- 

 prise typically fresh-water species. These are found 

 under varied conditions such as quiet pools in streams, 

 ponds, and lakes. Many of these species are widely 

 distributed, from south to north and from the coast to 

 the Sierra Nevada. 



Feeding. — The feeding mechanism of Corixidae is 

 unique among Hemiptera. The rostrum is completely 

 altered, forming a broad, cone-shaped apex of the 

 head. The stylets are used more for piercing and 

 rasping than for sucking and lack the well-defined 

 food and salivary channels that are so characteristic 

 of other Hemiptera. The mouth opening is on the face 

 of the broad "beak." It permits entry of entire organ- 

 isms of small size as well as the cell contents of 

 pierced strands of algae. Diatoms, rotifers, and other 

 whole organisms are ground up by the "masticator," 

 a structure of the buccal and pharyngeal region which 

 is generally lacking in other Hemiptera that ingest 

 only liquids. Griffith (1945) summarizes his studies 

 of the corixid diet with the statement that "the pres- 

 ence of algal, protozoan, and rotiferan remains in 

 adult stomachs indicates for Ramphocorixa acuminata 

 a diet neither wholly animal, nor vegetable. The 

 scooping movements of the forelegs seem designed 

 to winnow out of the ooze a nutritious salad from 

 both kingdoms, mixed in one digestible mass in the 

 pharyngeal grinder." In addition to this "salad" and 

 the habit of evacuating the cell contents of filamen- 

 tous algae, corixids capture and feed upon whole 

 chironomid and mosquito larvae. 



Respiration. — Corixids differ from other water bugs 

 in the manner in which they renew the air in their 

 plastron. Notonectids, naucorids, and dytiscids break 

 the surface film with the posterior end of the body. 

 Corixids break the surface with the head and pronotum, 

 so quickly that it is difficult to observe. Because of 

 the extensive plastron surface corixids are able to 

 remain below the surface for comparatively long 

 periods of time, using oxygen which diffuses into the 

 bubble from the water. 



Life History. — Hungerford (1920) has worked out 

 the life history of one of our commonest corixids, 

 Sigara alternata (Say). The winter is passed in the 

 adult stage, "the adults exhibiting considerable 

 activity even in waters covered by a layer of ice." 

 Eggs are laid in the spring and are attached to stems 



Fig. 7:4. Eggs of Corixidae. a, Sigara alternata (Say); b, 

 Cenocor/'xo bifida (Hungerford); c, Corisella edulis (Champion); 

 d, Graptocorixa abdominalis (Say) (Hungerford, 1948a). 



and leaves of various water plants, sticks, boards, 

 and even the shells of living snails. The incubation 

 period was one to two weeks at Ithaca, New York. 

 The five nymphal instars required about one week each 

 except the last stage which occupied a few days 

 longer. Approximately the same sequence was ob- 

 served for Corisella edulis by Griffith (1945). 



The various nymphal instars may be recognized 

 apart from the sequence of sizes, by the progressive 

 development of the hemelytral pads. First instars 

 show no prolongation of the posterolateral margins 

 of the mesothorax; in second instars the hind margin 

 is sinuate sublaterally; in third instars the hemelytral 

 pads are half as long as the entire thorax; in fourth 

 instars the pads attain the level of the first abdominal 

 segment; and in fifth instars they reach the middle 

 of the third abdominal segment. 



Eggs. — Hungerford (1948) describes eggs of thirty 

 species of Corixidae, six of which occur in California. 

 All the California genera are represented. In general 

 the eggs are ovoid but not symmetrical, being more 

 convex on one side than the other and the surface is 

 hexagonally reticulate. The egg is fastened on a 

 pedestal and has a nipple at the apical or micropylar 

 end (fig. 7:4). 



Relationships. — The family Corixidae is placed in 

 the suborder Cryptocerata by most recent authors 

 because of the reduced antennae. However, this is a 

 superficial criterion. Others, recognizing the unique 

 mouth parts, have proposed the series Sandaliorrhyncha 

 for this group of water bugs alone. Some doubt was 

 cast on this extreme view by the studies of Singh- 

 Pruthi, who found that the male genitalia are not 

 inconsistent with the basic pattern found among other 

 aquatic Hemiptera. At present, then, the true relation- 

 ships of the family are not clear, but the three pairs 

 of nymphal scent gland openings and the peculiar 

 mouth parts set the family apart from all other water 

 bugs. An Australasian genus Diaprepocoris, which is 



