201 

 Usinger: Hemiptera 



hair pile provides, a very thin but virtually incom- 

 pressible air store or "plastron" which enables the 

 insect to remain below the surface in well-oxygenated 

 waters for an indefinite period, extracting dissolved 

 oxvgen from the water. Lacking a subelytral air store, 

 Aphelocheirus has no "hydrostatic" mechanism. 

 Therefore, special pressure receptors are developed 

 at the base of the abdomen to aid in orientation. 



Life history (Usinger, 1946).— The life history of 

 the common genera of Naucoridae is relatively simple 

 (fig. 7:12). The winter is passed in the adult stage. 

 Eggs are laid in the spring, the eggs in our species 

 being glued to stones in shallow waters of lakes and 

 streams. The eggs are suboval with a small, buttonlike 

 micropyle at the anterior end. When first laid, they 

 are cream-colored, but they change to gray with 

 reddish eyespots in a week or so. Hatching occurred 

 in about four weeks in the Sacramento Valley (Ambry- 

 sus mormon), the nymph emerging through a crescent- 

 shaped tear at the micropylar end of the egg. The 

 first four nymphal instars each required about a week 

 during May, June, and July, whereas the fifth and 

 last instar required three weeks. Adults fly by day, 

 but this must be a rare phenomenon because I have 

 observed it only once. They do not fly to lights at 

 night but are attracted to a light held near the water. 



Nymphal instars may be determined by the following 

 table (7:2), based upon Ambrysus mormon Montd. In 

 the fifth nymphal instar the lateral margins of the 

 mesonotum (hemelytral pads) completely cover the 

 metanotal pads. 



Habitat and distribution.-** Naucorids occur in a wide 

 variety of habitats including ponds, lakes, rivers, hot 

 springs, and saline waters. In the United States 

 Cryphocricos is a Neotropical group which extends 

 only into southern Texas where it inhabits swift- 

 flowing streams. Usingerina is the northernmost repre- 

 sentative of the Neotropical subfamily Limnocorinae. 



Pelocoris is the only genus of Naucoridae found 

 in the eastern United States. In the West, it has been 

 found only in two hot springs in Nevada and at Sara- 

 toga Springs, Death Valley, California. Pelocoris 

 occurs in quiet waters and is commonly found amidst 

 aquatic vegetation. 



Ambrysus is the dominant naucorid genus throughout 

 the western United States. It ranges from the hot 

 springs of Yellowstone to Argentina. In general, 

 Ambrysus species are found in clear flowing, well- 

 oxygenated waters, especially those with pebbly or 

 rocky bottoms. Although the preferred habitat seems 

 to be streams, Ambrysus mormon, at least, invades 

 the margins of lakes within its range. Thus Clear 



TABLE 7:2 



Development of Hemelytral Pads in Successive 

 Instars of Ambrysus mormon (Montd.) 





1st 

 instar 



2d 

 instar 



3d 



instar 



4th 

 instar 



5th 



instar 



Ratio of lateral 

 margin of meso- 

 notum to lateral 

 margin of meta- 

 notum 



1:2 



2:3 



1:1 



2:1 



1:0 



Fig. 7:13. Usingerina moapensis La Rivers, female, Warm Springs, 

 Clark County, Nevada, December 26-27, 1948 (La Rivers). 



Lake and Eagle Lake are inhabited by this species, 

 and the specimens from Clear Lake appear to be 

 slightly smaller and darker than usual, whereas the 

 opposite is true for Eagle Lake in Lassen County. 

 Ambrysus mormon has been taken also in shallow 

 water at the north end of Lake Tahoe. It is most 

 abundant, however, in the saline waters of Pyramid 

 Lake, Nevada, where it is the dominant insect. 



In spite of interesting local occurrences in lakes, 

 Ambrysus mormon is typically an inhabitant of streams. 

 It occurs in all the streams draining into the Sacra- 

 mento and San Joaquin valleys from the Sierra Nevada 

 and from the Coast Ranges. It is abundant in north 

 coastal streams such as the Eel River. In southern 

 California it is replaced by Ambrysus occidentalis 

 (= Ambrysus signoreti of authors, not Stal 1862). 

 Coincident in range with both of these, at least in 

 coastal streams, and sometimes found in the same 

 streams is Ambrysus californicus, a smaller pale 

 green species. The typical form is found in southern 

 California, whereas a form with spined connexival 

 angles occurs in northern California. 



The largest Ambrysus known from California is 

 A. puncticollis. This species occurs in streams 

 draining into the Colorado River and has been taken 

 near Parker Dam on both the California and Arizona 

 sides of the river. 



By far the most local species in California are 

 Ambrysus funebris and A. amargosus. These little 

 species have thus far been taken only in the water 



