197 

 Usinger: Hemiptera 



Fig. 7:10. a, Notonecta unifasciata Guerin, male, Davis, Yolo County, California, June 12, 

 1932 (R. L. Usinger); b, Buenoo scimitra Bare, male, Walnut Creek, Contra Costa County, Cali- 

 fornia, July 9, 1929 (R. L. Usinger). 



with the other aquatic families, except Corixidae, in 

 the Notonectoidea. They appear to be somewhat 

 isolated from the naucoroid type by the elongate, 

 deep-bodied form, absence of dorsal abdominal scent 

 glands in the nymphs, and back-swimming habit. Yet 

 in male genitalia and in egg type, they are closest 

 to the naucoroid families and are somewhat distinct 

 from the belostomatids, nepids, and corixids. The 

 Pleidae are now generally given family rank but are 

 closely related to notonectids. They are very small, 

 suboval bugs with hind legs that are not oarlike, 

 though possessing swimming hairs. The abdominal 

 venter is not narrowly keeled but rather is elevated 

 into variously formed carinae at the middle of each 

 segment. 



Respiration. — Like so many water bugs, notonectids 

 come to the surface at intervals to replenish their 

 supply of air. The surface film is broken by the tip 

 of the abdomen with the' bug suspended, head down- 

 ward at an angle and swimming legs outstretched. 

 Air enters the abdominal troughs where it comes in 

 contact with the ventral spiracles and diffuses for- 

 ward to the thoracic spiracles and to the subelytral 

 air spaces. 



In Buenoa and its close old-world ally, Anisops, a 

 red color is clearly visible through the thin body 



wall. Hungerford (1922) first reported that the color 

 is due to hemoglobin, and Bare (1928) found that it 

 occurs in large cells that surround the tracheae in 

 abdominal segments three to seven. In some cross 

 sections nearly one-third of the abdominal space is 

 occupied by hemoglobin cells. The function of hemo- 

 globin in these bugs is not known, but it would be 

 logical to assume that it is in some way associated 

 with respiration or hydrostatic equilibrium. 



Life history. — Most notonectids overwinter in the 

 adult stage, either actively or in hibernation, depend- 

 ing on the climate. Hungerford (1933) reports that 

 Notonecta has been observed swimming beneath the 

 ice in midwinter. Eggs are laid in the spring and 

 summer, there being one or more overlapping broods 

 in a season. However, Rice (1954) reported that 

 Notonecta borealis passes the winter in the egg 

 stage and suggested that two species of Buenoa may 

 do likewise. 



Eggs are laid in plant tissue or on plant or rock 

 surfaces. Rice (1954) found that eggs of Plea, Buenoa, 

 and two species of Notonecta from Douglas Lake 

 region (Michigan) were inserted in stems and those of 

 three other Notonecta species were not inserted. All 

 eggs that were glued to the surface of stems had 

 characteristic hexagonal reticulations, and those 



