198 



Usinger: Hemiptera 



which were inserted had characteristic nodules in 

 addition to hexagonal ridges. Buenoa eggs differ from 

 those of Notonecta and Plea in having a distinct 

 anterodorsal cap. The incubation period varies with 

 the season and species. There are five nymphal 

 instars in all species studied. 



Habits and distribution. — Back swimmers occur in a 

 wide variety of fresh and stagnant pools and in the 

 quiet water of streams and lakes. In California they 

 are found from sea level to high elevations in the 

 Sierra Nevada. Food consists of small Crustacea, 

 chironomids, mosquito larvae, fish fry, and in fact 

 anything that they can overpower. 



Adults fly readily and disperse over considerable 

 distances. Hungerford (1933) reports swarms in flight 

 and says that they are attracted to lights. Walton 

 (1935), in a series of experiments with Notonecta 

 maculata (Fabr.) in Britain, carried specimens away 

 from water for distances ranging from one and a half 

 to thirty yards. After drying on the ground 200 bugs 

 took wing and of these 45 per cent were seen to drop 

 into water. 



Pierce (1948) described a new species, Notonecta 

 badia, from the McKittrick asphalt field, Kern County, 

 and reported that Notonecta was also present in the 

 Los Angeles La Brea deposits. According to Pierce, 

 the age "is unquestionably Pleistocene, because all 

 of the recovered fragments come from the skull cav- 

 ities of saber-tooth cats." 



Stridulation. — Definite chirping sounds have been 

 recorded for Buenoa by Hungerford (1924). Several 

 structures are described by Bare (1928) as possible 

 stridulatory organs. The most obvious of these are 

 the stridulatory comb at the base of the male tibia 

 and the rostral prong with filelike teeth that stands 

 in opposition when the fore limbs are brought up to 

 the head. Also reportedly of use in sound production 

 are the fine sclerotized ridges on the inner face of 

 the fore femur. 



The habits of Buenoa and Notonecta are strikingly 

 different as stated by Truxal (1953). "The Buenoa 

 swim gracefully on their backs in almost perfect 

 equilibrium with the water." Thus, in a sense, Buenoa 

 could be described as limnetic. Notonecta, on the 

 other hand, are jerky swimmers, working constantly 

 to maintain their position in the water when they 

 are not clinging to some object or hanging from the 

 surface film. 



In distributional pattern, the notonectoid genera 

 present an unusual picture. Notonecta is world-wide 

 but Buenoa is restricted to the Western Hemisphere 

 and Hawaii. The Pleidae are most abundant in the 

 tropics but extend into temperate regions including 

 the southern and eastern United States. They have 

 not yet been found in the Pacific states. 



Taxonomic characters. — The principal characters 

 used in classification include the male genitalia, 

 which differ in most species but must be dissected 

 out and therefore are not used in the present keys. 

 Stridulatory ridges on the fore femora of Buenoa can 

 be seen only if the front legs are bent outward or 

 detached and mounted on a card. Measurements, in- 

 cluding the synthlipsis (narrowest point of interocular 



space at hind margins of eyes) and vertex (anterior 

 interocular width), should be made with the transverse 

 and longitudinal axes of the insect horizontal. The 

 length of the rostral prong in Buenoa is measured by 

 holding the insect so that the surface of the prong 

 is horizontal. 



Key to the Nearctic Genera of Notonectidae 



Adults 



1. Hemelytral commissure with a pit at anterior end, just 

 behind tip of scutellum; antennae 3-segmented, the last 

 segment longer than penultimate segment; relatively 



small, slender, 5 to 8 mm. (fig. 7: 106) 



Buenoa Kirkaldy 1904 



— Hemelytral commissure without a pit; antennae 4-seg- 

 mented, the last segment much shorter than penultimate 



segment, robust, more than 10 mm. (fig. 7:10a) 



Notonecta Linnaeus 1758 



Nymphs 



1. Abdominal spiracles large, oval, about 1/4 as long as 

 segments, located mesad of ventral hair fringe; hind 



legs without rows of conspicuous, stout spines 



Buenoa 



— Abdominal spiracles small, round, less than 1/10 as 

 long as segments; hind legs with rows of short, stout, 

 black spines Notonecta 



Key to the California Species of Notonecta 1 



1. Keel of 4th abdominal sternite bare, hairs confined to 

 sides 2 



— Keel of 4th abdominal sternite not bare 3 



2. Head broad, 5/6 as wide as pronotum; eyes large, rear 

 width of one eye as great as length of lateral margin of 

 pronotum; scutellum 1/2 again as broad as long; 

 southern California hoffmanni Hungerford 1925 



— Head narrower, 2/3 as wide as pronotum; eyes smaller, 

 rear width distinctly less than length of lateral margin 

 of pronotum; scutellum less than 1/4 broader than 

 long; widespread kirbyi Hungerford 1925 



3. Pronotum distinctly longer than scutellum; males with 

 a stout tubercle at angle of fore trochanter and a very 

 stout broad hook; dichromatic, one form white, the 

 other black, marked with white; widespread 



shooterii Uhler 1894 



— Pronotum distinctly shorter than scutellum; males 

 without a tubercle or hook on fore trochanter 4 



4. Trochanter of middle legs rounded or nearly so 5 



— Trochanter of middle legs distinctly angulate or pro- 

 duced into a tooth or stout, spinelike process 6 



5. Lateral margins of pronotum distinctly though shallowly 

 concave; length 10-11 mm., last abdominal sternite of 

 female scarcely or shallowly notched at tip, the notch 

 wider than deep; Imperial Valley indica Linn. 1771 



— Lateral margins of pronotum straight; length usually 

 larger, 11-12 mm.; last abdominal sternite of female 

 with an apical notch which is deeper than wide; wide- 

 spread undulata Say 1832 



6. Middle trochanter angulate or produced into a short 

 tooth at inner posterior angle (fig. 7:10a); widespread 



unifasciata Guerin 1857 2 



'Excluded from key: N. ochrothoe Kirk. 1897, a South American 

 species not clearly distinguishable from /V. shooterii, with a 

 single doubtful California record, San Diego, one specimen. 



2 Hungerford (1933) divided unifasciata into several subspecies, 

 based on the shape of the vertex and male genital clasper. 

 California specimens pertain to the subspecies andersoni which 



