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Home , Ambrysus, Ambrysus amargosus, Ambrysus mormon, Hot Creek (Mono County), Hot spring, Hydrometra australis

Polhemus and Polhemus: Aquatic of Desert Hot Springs 1

A preliminary survey of the aquatic and semiaquatic Hemiptera occurring in the springs of the Railroad , White , and Amargosa River drainage systems, and , with special reference to thermal relicts

Dan A. Polhemus Dept. of Entomology, Bishop Museum, P. 0. Box 19000-A, Honolulu, HI 96817

ard

John T. Polhemus Univ. of Museum, 3115 S. York St., Englewood, CO 80110

INTRODUCTION

One of the most remarkable concentrations of disjunct and endemic aquatic Hemiptera in North America is found in the thermal refugia of the Railroad Valley, White River, and Amargosa River drainages of Nevada and California. These drainages represent former to the Colorado system that were continuous systems in the Pliocene and Pleistocene, but have been subsequently dessicated and reduced to discontinous fed aquatic refugia. The thermal springs of these three systems contain a large number of endemic aquatic Hemiptera species, as well as many highly disjunct populations of other taxa. The report details the distributions of these species, addresses certain taxonomic problems relating to them, and considers the biogeographic significance of this thermally relictual fauna.

LOCALITIES SAMPLED

The information upon which this report is based has been collected by the authors over a period of thirty years, and in many cases the passage of several decades has seen a serious degredation of the aquatic habita~s listed below. For this reason an attempt has been made in the last three years to revisit many of the most critical and &scertain the status of their aquatic Hemiptera faunas. As a result, some habitats have multiple dates and CL (collection locality) numbers listed after them, each representing a separate visit. All of the collections below were made by J. T. and D. A. Polhemus unless otherwise noted; a notation (DAP) indicates only the first author was involved in the survey, and a notation (JTP) indicates only the second author. All specimens collected during these surveys are held in the J. T. Polhemus collection, Englewood, ·colorado.

White River Drainage

NEVADA, White Pine Co., Lund Town Spring at Lund, 5600 ft., water temp. 19° C., 20 July 1992, CL 2705; 27 June 1993, CL 2895. NEVADA, Nye Co., Emigrant Spring, 17 mi. S. of Lund, 5500 ft., water temp. 20° C., 20 July 1992, CL 2707. NEVADA, Nye Co., Butterfield Springs, near Sunnyside, 5270 ft. , water temp. 17° C. , 27 June 1993, CL 2896. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 2

NEVADA, Nye Co., Flagg Springs, near Sunnyside, 5280 ft., water temp. 17° C., 27 June 1993, CL 2897. NEVADA, Nye Co., Spring, 6 mi. W. of Sunnyside, 5200 ft ., water temp. 30° C. in spring head and outflow, 24° C. in adjoining marsh, 27 June 1993, CL 2898. NEVADA, White Pine Co., Gardner Ranch , 19 mi. NW of Lund, 6300 ft., water temp. 51 o C. at spring head, 41 o C. in outflow, 20 July 1992, CL 2706 NEVADA, Nye Co., Moorman Warm Spring, SW of Lund, 5300 ft., water temp. 36° C., 20 July 1992, CL 2708; 27 June 1993, CL 2899. NEVADA, Lincoln Co., Hiko Spring at Hiko, 4150 ft., water temp. 26° C., 20 July 1992, CL 2709. NEVADA, Lincoln Co., Crystal Spring, S. of Hiko, 4050 ft., water temp. 28° C., 20 July 1992 and 21 July 1992, CL 2710. NEVADA, Lincoln Co., Ash Warm Springs, 3750 ft ., water temp. 36° C., 21 July 1992, CL 2711. NEVADA, Clark Co., Moapa Warm Springs, N. of Moapa, 1800 ft, water temp. 32° C., 22 February 1964 (JTP), CL 281; 13 April 1968 (JTP), CL 423; 23 November 1984 (DAP); 23 July 1992, CL 2720.

Railroad Valley

NEVADA, Nye Co., Big Warm Spring at Duckwater, 5800 ft. , water temp. 33° C., 27 June 1993, CL 2893. NEVADA, Nye Co., Little Warm Spring at Duckwater, 5800 ft. , water temp. 33° C., 27 June 1993, CL 2894. NEVADA, Nye Co., spring and outflow crossing highway at Lockes Ranch, 5000 ft., water temp. 32° C. at spring head, 25° C. in outflow, 28 June 1993, CL 2900. NEVADA, Nye Co., outflow at Twin Springs, 10 mi. E. of Warm Springs, 5250 ft., water temp. 25° C., 21 July 1992, CL 2712.

Amargosa River System

CALIFORNIA, lnyo Co., Shoshone Warm Spring at Shoshone, 1800 ft ., water temp. 33° C., 29 June 1993, CL 2904. CALIFORNIA, lnyo Co., Tecopa Hot Springs, 1750 ft., water temp. 37° C., 27 February 1964 (JTP), CL 280; 29 June 1993, CL 2903. CALIFORNIA, San Bernardino Co., Saratoga Spring, Death Valley Nat. Mon., 200 ft., water temp. 28° C., 21 February 1964 (JTP), CL 278; 29 June 1993, CL 2902. CALIFORNIA, lnyo Co., Grapevine Springs, Death Valley Nat. Mon., 2750 ft., water temp. 35° C., 28 June 1993, CL 2901 . CALIFORNIA, lnyo Co., Spring, Death Valley Nat. Mon., 21 February 1964 (JTP), CL 273; 24 November 1984 (DAP). CALIFORNIA, lnyo Co., Nevares Ranch springs, Death Valley Nat. Mon., 8 April 1968 (JTP), CL 421. NEVADA, Nye Co., Jackrabbit Spring, Ash Meadows National Wildlife Refuge, 20 February 1964 (JTP), CL 270. NEVADA, Nye Co., Point of Rocks Spring, Ash Meadows National Wildlife Refuge, 2350 ft ., water temp. 32° C., 20 February 1964 (JTP), CL 269; 25 November 1984 (DAP) ; 22 July 1992, CL 2713. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 3

NEVADA, Nye Co., North Scruggs Spring, Ash Meadows National Wildlife Refuge, 2330 ft., water temp. 33° C., 22 July 1992, CL 2714. NEVADA, Nye Co., South Scruggs Spring, Ash Meadows National Wildlife Refuge, 2330 ft., water temp. 33° C., 22 July 1992, CL 2715. NEVADA, Nye Co., Marsh Spring, Ash Meadows NWR, 2330 ft ., water temp. 31.5° C., 22 July 1992, CL 2716. NEVADA, Nye Co., North Indian Spring, Ash Meadows National Wildlife Refuge, 2330 ft ., water temp. 31 o C., 22 July 1992, CL 2717. NEVADA, Nye Co., Purgatory Well, Ash Meadows NWR, 2350 ft., water temp. 33.5° C., 22 July 1992, CL 2718. NEVADA, Nye Co., Mary Scott Spring, Ash Meadows National Wildlife Refuge, 2350 ft ., water temp. 28° C., 22 July 1992, CL 2719. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 4

RESULTS

The species collected from the localities in the preceding list are summarized in Table 1 below.

Table 1: Aquatic Hemiptera species known from springs in the Amargosa River, White River, and Railroad Valley drainage systems

The table below lists the known aquatic Hemiptera faunas of various cold and thermal springs sampled in the major remaining aquatic refugia in these river systems, and indicates the status of the species involved. Codes used in the table are a follows: E = endemic to a single spring or group of springs in close proximity to one another; D = notably disjunct species population. This table also contains data gathered by other collectors, but included so as to provide a more complete faunal profile of each particular spring. Certain thermal spring water temperatures were taken from Waring (1965).

Locality Water temp. Tax a present

RAILROAD VALLEY Duckwater Big Warm Spring BELOSTOMATIDAE Belostoma bakeri (D) Pelocoris shoshone shoshone (D) SALDIDAE Micracanthja humjlis ~buenoj Saldula pallipes

Little Warm Spring . BELOSTOMATIDAE Belostoma bakeri (D) NAUCORIDAE Pelocoris shoshone shoshone (D) SALDIDAE Saldula palustris

Lockes Ranch spring at highway BELOSTOMATIDAE (name uncertain) Belostoma bakeri (D) CORIXIDAE Corisella decolor Hesperocorixa laeviqata GERRIDAE Gerris qjllettej unifasciata unjfascjata Microvelia beameri '.. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 5

Twin Springs Valley Twin Springs CORIXIDAE Hesperocorjxa laeyjgata GERRIDAE Gerrjs gillettej NOTONECTIDAE Notonecta urijfascjata

WHITE RIVER SYSTEM Upper White River Lund Town Spring BELOSTOMATIDAE Belostoma sp. undet.1 (D) CORIXIDAE Graptocorjxa serrulata GERRIDAE Gerris gillettei NOTONECTIDAE Notonecta Jill:b.ri

Emigrant Springs BELOSTOMATIDAE Belostoma saratogae (D) CORIXIDAE Hesperocorjxa laeyjgata GERRIDAE Gerrjs gillettej NOTONECTIDAE Notonecta lslr.tlri SALDIDAE Saldula palustrjs VELIIDAE Microvelia beamerj

Butterfield Springs GERRIDAE Aguarius remigis NAUCORIDAE woodburyi (D)

Flagg Springs NAUCORIDAE Ambrysus woodburyj (D)

Gardner Ranch Hot Spring SALDIDAE Saldula comatula

Moorman Hot Spring BELOSTOMATIDAE Belostoma saratogae (D) CORIXIDAE Hesperocorjxa laevigata GERRIDAE Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 6

Gerrjs gjllettej NOTQ\JECTIDAE Notonecta unjfascjata unjfasciata SALDIDAE Saldula~

Hot Creek Spring BELOSTOMATIDAE Belostoma & (D) NAUCORIDAE (D) NOTQ\JECTIDAE Notonecta unjfascjata andersonj VELIIDAE Rhagovelia djstincta (D) Hiko Spring BELOSTOMATIDAE Belostoma sp. (imm. only) CORIXIDAE Hesperocorixa laevigata NOTQ\JECTIDAE Notonecta unjfasciata SALDIDAE Saldula palustris

Crystal Spring BELOSTOMATIDAE Belostoma bakerj (D) Hydrometra australis (D) VELIIDAE Rhagovelia distincta (D)

Ash Warm Spring BELOSTOMATIDAE Be lostoma bakerj (D) NAUCORIDAE Ambrysus mormon (D) Pelocoris shoshone shoshone (D)

Moapa River Moapa Warm Springs BELOSTOMATIDAE Belostoma fluminium NAUCORIDAE Ambrysus mormon Pelocoris shoshone shoshone (D) Usingerina moapensis (E) VELIIDAE Rhagoyelja ~ (D) Rhagovelia djstincta Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 7

AMARGOSA RIVER SYSTEM Ash Meadows Point of Rock Springs NAL.JCORIDAE {E) Pelocorjs shoshone amargosus {D) SALDIDAE Micracantbja bumjlis VELIIDAE Rbagovelja distincta {D)

North Scruggs Spring GEL.ASTOCORIDAE Nertbra martini {D) NAUCORIDAE Ambrysus n.sp. {E)

South Scruggs Spring NAUCORIDAE Ambrysus n.sp. {E) Pelocorjs shoshone amargosus VELIIDAE Microvelia sp.

Marsh Spring 31.5° C. NAUCORIDAE Ambrysus n.sp. {E)

North Indian Spring 30° C. NAL.JCORIDAE Ambrysus n.sp. {E)

Purgatory Well 33.5° C. BELOSTOMATIDAE Belostoma saratogae {D) NAUCORIDAE Ambrysus sp. undet. {imm. only) Pelocoris shoshone amargosus {D) NOTONECTIDAE Notonecta unifasciata unifasciata VELIIDAE Mjcrovelia sp.

Mary Scott Spring NAL.JCORIDAE Pelocoris shoshone amamosus {D)

Shaft/Chalk Spring ?? NAUCORIDAE Ambrysus sp. undet. {imm. only) Pelocorjs shoshone amargosus {D)

Claypit Spring ?? NAUCORIDAE Pelocoris shQshone amargQsus {D)

Jackrabbit Spring ?? NAL.JCORIDAE Ambrysus mQ rmon {D) ·. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 8

Middle Amargosa Tecopa Hot Springs 37° c NAUCORIDAE (warm marsh) Pelocorjs shoshone amargosus (D) NOTONECTIDAE Notonecta unjfasciata unjfasciata

Shoshone Hot Spring 33° c NAUCORIDAE Ambrysus mormon (D) Pelocorjs shoshone amargosus (D)

Resting Spring 27° c VELIIDAE Rhagovelia distincta (D)

Death Valley Saratoga Spring 28° C BELOSTOMATIDAE Belostoma saratogae (E) Lethocerus angustjpes (D) GELASTOCORIDAE Nerthra martini (D) HYDROMETRIDAE Hydrometra australis (D) MESOVELIIDAE Mesoyelia amoena NAUCORIDAE Pelocorjs shoshone amamosus (D) NOTONECTIDAE Buenoa scimitra Notonecta undulata SALDIDAE Pentacora saratogae (D) Saldula opiparja VELI IDAE Microvelia .hl.!:l.ai

Sheep Creek Spring ?? NAUCORIDAE Pelocoris shoshone amaraosus (D) NOTONECTIDAE Buenoa scimitra

Travertine Springs 36° c MESOVELIIDAE Mesovelia amoena NAUCORIDAE Ambrysus funebris (E)

Cow Creek Springs 36° c GELASTOCORIDAE (Nevares Ranch) Nerthra martini (D) Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 9

MESOVEUIDAE Mesoyelia amoena NALCORIDAE Ambrysus funebrjs (E)

Limestone Spring ?? NALCORIDAE Ambrysus funebrjs (E)

Grapevine Springs NAUCORIDAE Pelocorjs shoshone shoshone (D) SALDIDAE Saldula~

Notes: 1 = females only

TAXONOMY

The taxonomic interpretations given in Table 1 above are those currently valid under existing nomenclature, and are for the most part stable. In a few cases, however, the of the groups involved is coming under renewed scrutiny, and formerly accepted species concepts are likely to be revised in the next several years. This section reviews the situation in four genera that are currently under study by specialists.

Belostomatidae

Belostoma - Belostoma saratoaae was described by Menke (1958) based on a series of specimens from Saratoga Spring, in southern Death Valley. All subsequent workers have considered this a valid species confined to this single thermal spring . Recent collections of Belostoma from across the American Southwest, however, have revealed that the characters used to separate .a. saratogae from the more widespread and closely related .a . ~ are variable, and that the two species in fact appear to blend into each other. All character sets so far examined provide conflicting diagnoses; these include male phallic characters, airstrap measurements, and head structure. Despite this, there may still be two species involved, and they may segregate on the basis of thermal versus cold spring habitats. At Moorman Hot Spring, for instance, it is possible to distinguish a single male taken in the cold marsh from another long series of males taken in the warm waters of the outflow creek. If one bases the diagnosis soley on the ventral diverticulum of the phallus and ignores all other characters, then the "warm" specimens from Moorman are .a. bals..eri. and the "cold" specimen is .a. saratogae. The situation at other spring fed habitats around the region is less clear, and provides no clear geographic or ecological pattern. The populations inhabiting the thermal springs at Duckwater and Lockes Ranch in Railroad Valley run to .6.. ~ in comparison to other populations in the region, whereas specimens from thermal waters at Hot Creek along the upper White River appear to be .a. saratogae. Most of the specimens from thermal springs in Ash Meadows, on the middle Amargosa, conform to a broad interpretation of .a. saratogae, except for a few indeterminate specimens from a cool water marsh. The population at the Saratoga Spring type locality conforms to the Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 10 original description, but the airstrap measurements are variable even within this population and are not nearly as definitive a character as stated by Menke (1958). Given the above observations, it is reasonable to propose that a. saratogae is no more than a synonym of a. .b..aJse.d. At the same time, the Belostoma populations in the Railroad Valley, White River, and Amargosa River systems when taken as a whole appear to represent a variable but related complex, which can in turn be separated consistently from populations of a. b..a.ls..a.ri. occurring in surrounding regions. It may thus be necessary to redefine the entire insular complex as a. saratogae, and to interpret this species as being much more widespread and variable than was previously believed. All related populations outside the three basins noted above would then be considered .a.. ~. The only· specimens failing to conform to this arrangement are a series from San Diego, California, that appear to fall within the new "broad" concept of a. saratogae. This latter distribution is of interest biogeographically in light of hypotheses that the Mojave River once had a connection to the Pacific Ocean via the Los Angeles Basin. One additional Belostoma species, a. flumineum, is found in the region under discussion, occurring at Moapa Warm Springs on the lower White River. However this species, which is a transcontinental taxon widespread throughout the system and the interior valleys of California, is quite distinct morphologically from the saratogae/bakerj complex, and its distribution thus has little bearing on the above analysis.

Naucoridae

Usjngerjna - The monotypic genus Usjngerjna is confined to Moapa Warm Springs, and is one of only two taxa in the subfamily Limnocorinae occurring in the , the other being Umnocoris l.u..lti. which is found in Texas. The primary character used by La (1950) to separate Usjngerjna from Limnocorjs was the hooked shape of the hemelytral embolium in the former. The suitability of this character as a basis for generic level separation has been questioned by several authors (De Carlo, 1951; Sites, in press), who have advocated transferring Usjngerjna moapensjs, the only species in the genus, to Limnocorjs, and synonymizing the former genus under the latter.

Pelocoris shoshone - La Rivers (1949a) described Pelocoris shoshone from material taken at Ash Warm Springs, along the middle White River, and subsequently reported additional specimens from Moapa Warm Springs, on the lower White (La Rivers, 1950). Several years later an additional population of this species was located at Saratoga Spring in Death Valley, which La Rivers (1956) interpreted to represent a separate subspecies, f. shoshone amargosus. Although these discoveries were remarkable at the time, since Pelocoris was considered to be a Neotropical genus confined to the southern and eastern United States, further collecting over the last thirty years has revealed that Pelocorjs is in fact widespread as a series of disjunct populations throughout the southern . Pelocorjs shoshone is now known not only from the Ash Warm Spring, Moapa Warm Spring, and Saratoga Spring localities that La Rivers reported, but also from Sheep Creek and Grapevine Springs in Death Valley, Tecopa and Shoshone warm springs along the middle Amargosa River, many springs at Ash Meadows, and the warm springs at Duckwater in northern Railroad Valley (see Table 1). La Rivers (1956) indicated that Pelocorjs shoshone shoshone was confined to the White River drainage, while .e. shoshone amargosus occurred in the Amargosa Basin. Although intuitively appealing, this hypothesis of distribution has been disproven by subsequent collections, which demonstrate that the characters used to separate the two .. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 1 1

subspecies, size and color, are weak and intergrade between the many populations now known. Using a rather strict application of La Rivers (1956) diagnosis for E.. shoshone amargosus, it appears that the only populations in the southern Great Basin that truly conform to his concept are those from Saratoga Spring, Tecopa Hot Springs, and Shoshone Hot Spring, all of these localities lying in the Amargosa Basin. Collecting in the southwestern United States and Mexico has revealed, however, that this subspecies also occurs in the Atascosa Mountains of far southern Arizona (at Sycamore ), and along the western foothills of the Sierra Madre Occidental in Sonora. All of the remaining Pelocorjs populations in the southern Great Basin, including those in northern Death Valley, Ash Meadows, Railroad Valley, and the White River drainage, conform in greater or lesser degree to La Rivers (1949a) concept of E.. shoshone shoshone, a subspecies that apparently does not have a wider distribution. The taxonomic situation is further complicated by the possibility that E.. shoshone is a synonym of E.. biimpressus, a poorly known species described by Montandon (1898) from Texas. Even if this proves to be the case, the status and distribution of the subspecies discussed above would still be a matter requiring resolution.

Ambrysus mormon - Montandon (1909) described Ambrysus mormon on the basis of a type series collected at St. George, Utah. This species is widespread throughout the American West, and exhibits a large degree of morphological variation across this range. In particular, populations inhabiting thermal waters tend to be dwarfed and display distinctive and consistent morphological differences. Two subspecies have been described from such habitats, A. mormon hejdemannj from the Firehole River in Yellowstone (Montandon, 191 0), and 8.. mormon minor from warm springs along the Owyhee River near Bruneau, (La Rivers, 1963). Similar trends toward morphological differentiation in thermal spring populations are also seen in the southern Great Basin, particularly with regard to the population at Ash Warm Spring, on the middle White River. It is uncertain yet as to whether the Ash Warm Spring population will merit recognition as a distinct subspecies, pending a detailed analysis of intraspecific morphological variation in 8.. mormon across its entire geographic range.

Notonectidae

Notonecta unifasciata - This species was described by Guerin (1857) from specimens taken in central Mexico. Hu'ngerford (1933) listed this species as occurring from South America to British Colombia, and recognized several subspecies. ,M. unjfascjata has a wide range of habitat tolerances, having been recorded from both hot springs and saline pools (including Francis Lake, near Tecopa, and and Saline Valley, in lnyo County), in addition to cool water habitats. Usinger (1956) considered all populations in mainland California to belong to the subspecies ,M. unjfascjata andersonj, but this interpretation does not hold for the populations found in the southern Great Basin. Although a population of N. unjfascjata andersonj apparently does occur in thermal waters at Hot Creek, along the upper White River, other specimens taken in the cool marsh below Moorman Hot Spring, less than twenty miles away, represent the nominate ,M. unjfasciata unifascjata instead. Based on the available collections, it seems that in the southern Great Basin N. unifasciata andersoni is found in thermal or saline waters, while ,M. unifascjata unifasciata is found in the cooler waters, such as marshes downstream from thermal outflows (see Table 1). These subspecies may be clinal, however, and any firm conclusions regarding their habitat partitioning must await a resolution of the taxonomic problems involved. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 12

Throughout the region under discussion N. unjfascjata as a whole is primarily a species of thermal springs, being found at Locke's Ranch and Twin Springs in Railroad Valley, Moorman and Hot Creek springs along the upper White River, Hiko Spring along the middle White River, and at several springs in Ash Meadows on the middle Amargosa River. By contrast, the cold springs of the upper White River at Lund and Emigrant, which are in close geographic proximity to the thermal outflows at Moorman and Hot Creek, harbor Notonecta ~. a species that has a distinct preference for cold water habitats. Also interesting is the presence of a third species, N. undulata. in the thermal Saratoga Spring in southern Death Valley, a habitat where one might otherwise expect to find N. unjfascjata once again.

DISCUSSION

Three major basins in California and Nevada contain significant concentrations of thermally endemic or highly disjunct aquatic Hemiptera: Railroad Valley, the White River basin, and the Amargosa River basin. All of these basins are hypothesized to have had previous connections to the Colorado River system. Railroad Valley and the White River lie in close proximity, being separated by a common drainage divide. The Amargosa River, by contrast, is more isolated, being separated from the previous two areas by a region of nearly waterless endorheic basins devoid of native fishes that has been termed the "Area of Sterile Basins" (Hubbs and Miller, 1948b), and by the northern tributaries of the present Colorado River system that drain into Las Vegas Wash (see fig. 1). These three areas and their relict aquatic Hemiptera faunas are discussed in greater detail below.

Railroad Valley

Railroad Valley is an extensive endorheic covering approximately 6000 square miles in central Nevada. The valley is hypothesized on the basis of biological and geomorphological evidence to have had a connection from its southern end to the Pahranagat Valley of the middle White River system via Penoyer and Desert Valleys (Hubbs and Miller, 1948b), but this connection, if it did exist, has long been severed. The former stream systems that fed pluvial Lake Railroad are now almost entirely dessciated, as is the lake itself, which exists only in the form of a remnant playa. The two largest thermal spring oases in the valley occur at Duckwater, in the far northern reaches, and at Lockes Ranch, along the western edge of the Railroad Lake playa below Black Rock Summit. Additional thermal springs are found at Hot Creek and Chimney Hot Springs, in the western and southern sections of the valley respectively, but their temperature is so high that they are unable to naturally support fish (although a fish refugium has been constructed below the outflow of the latter), and it is unknown whether they harbor thermally disunct aquatic . Complexes of cold springs, some with outflow creeks, are also present near Currant and along the eastern edge of the Railroad Lake playa, but like the hot springs noted above these have not yet been surveyed for aquatic Hemiptera. A synopsis of the spring fed habitats in Railroad Valley and their fish faunas was provided by Williams et al. (1985). The thermal springs at Duckwater are of large size, and support disjunct populations of both Belostoma ~ and Pelocorjs shoshone, this being the furthest northerly locality known for the latter species. Other genera such as Ambrysus and Rhagoyelia, which exist as disjunct populations in the thermal springs of the adjacent upper White River Basin, appear to be absent in Railroad Valley, although additional surveys are needed, particularly in the Locke's Ranch area where only brief collections have been undertaken. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 1 3

White River

The White River is now a dessicated drainage system that retains permanent flow only in three separate spring fed oases. These occur along the upper White River in the vicinity of Lund and Sunnyside, along the middle White in Pahranagat Valley, and along the terminal reach of the river at Moapa Warm Springs. Each of these oases is separated from the others by long, dry sections of ancient river devoid of surface flow, and as such they contain individually distinctive assemblages of endemic or disjunct aquatic Hemiptera species. The upper White River contains a large concentration of both cold and thermal springs, the former lying along the base of the Egan Range next to Nevada highway 318, and the latter emerging on the valley floor to the west of the dry river channel. An overview of these habitats and their fish faunas was provided by by Williams et al. (1985). The three major thermal outflows in the upper White River occur at Hot Creek, Moorman Hot Spring, and Moon River, the latter of which lies on private land and has not been accessible for surveys. The spring at Hot Creek is very large and feeds a deep outflow creek and adjacent cool water marsh. The outflow supports a disjunct population of Rhagoyelia distincta, representing the furthest northern record of this species in Nevada, and a thermally dwarfed population of Ambrysus mormon. The Moorman Hot Spring is smaller than the Hot Creek outflow, but is also in relatively natural condition, with a deep pool at the spring head, and a small formerly channelized outflow creek that runs for a considerable distance before feeding into a cool water marsh. The most notable disjunct faunal element at Moorman is Belostoma saratogae, which is abundant in the outflow channel. The cold springs of the upper White River support an aquatic Hemiptera assemblage distinct from that seen in the thermal waters, but with several interestingly disjunct populations of cold water species. Most notable among these is Ambrysus woodburyj, which is found at Sunnyside and Flagg Springs. This is the only occurrence of this species in Nevada; the next closest populations occur along the Virgin River in the vicinity of St. George, Utah, and along the Sevier River at Junction, in central Utah. Along the middle course of the White River are three large thermal springs which emerge in Pahranagat Valley, near Hiko. These springs, Hiko, Crystal and Ash, contain a diverse array of thermally endemic or disjunct aquatic , snail and fish taxa (Williams et al., 1985). Hiko Spring lies on a private ranch, and is the most disturbed and least entomologically interesting of the three springs in the valley. The spring gushes from the base of a hill at the north end of Hiko on property that in 1992 belonged to the Cannon Ranch. The spring head is enclosed in a concrete box with an open top, and discharges into a large, deep artificial basin approximately 20 meters in diameter. The outflow from this basin is channelled into a pipe and used for irrigation in the nearby valley bottom. A small amount of outflow seeps down from the basin and forms a muddy area in an adjacent horse pasture. Due to the highly altered nature of this habitat, and the presence of many introduced fish and aquatic plants, few aquatic now occur in the spring except for common Odonata species. Surveys here in July 1992 did not detect any remaining aquatic Heteroptera of interest. Crystal Spring lies in a grove of large cottonowood and willow trees just south of the junction of Nevada highways 375 and 318. Two large spring pools are present, discharging into a complex network of sloughs and flowing channels that finally coalesce into a single outflow exiting to the east, where there is a headgate. Although it apparently lies on private land, access to the spring is not controlled. The area is in a Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 1 4 relatively natural condition, although the margins of the outflow channels are heavily overgrown with exotic aquatic plants, and the waters contain numerous introduced fishes, especially convict cichlids. The large spring pools support Belostoma, while the outflow channels contain disjunct populations of Bhagoyelia djstjncta and Hydrometra australis, the latter being the only population of this species known in Nevada. Ash Warm Spring is the largest of the Pahranagat Valley springs, and has been the victim of numerous development attempts over the years, all of which have failed. Several spring outflows emerge from the base of a hill to the east of U. S. highway 93, flowing into an extensive series of deep, tree lined ponds. The best insect habitat lies at the northern end of this pond complex, adjacent to an area used by local residents for soaking, swimming and other recreation. Present here are Pelocorjs shoshone, which inhabits submerged vegetation along the margins of a small , and· the water beetle Stenelmjs callida moapa, which is found in the clear flowing water of the actual spring heads in areas where a substrate of clean sand is present. With a small amount of fencing the habitat most critical to these species could be protected from disturbance, while at the same time allowing the current recreational uses to continue. At the southern end of the ponds the combined waters from all the spring heads drain through a culvert under the highway and form a swift, shaded stream flowing down to the White River. This outflow stream harbors an extremely dense population of Ambrysus mormon, the individuals of which are morphologically divergent from typical populations of this species and may deserve subspecies status. The terminal reach of the White River, known as the Muddy River, still connects to the Virgin and thus to the Colorado. As a result, the lower section of the White River system has had more faunal interchange with the Colorado Basin in recent times than any of the other areas under discussion. Even so, the extensive Moapa Warm Springs oasis along this terminal reach retains perhaps the most distinctive aquatic fauna of any spring complex in the region, with many endemics and thermal disjuncts, most notable among these being the limnocorine naucorid Usjngerjna moapensjs and the veliid Bhagoyelja ~ (Polhemus, 1973), both of which are unknown elsewhere in the Virgin or Colorado systems. Several thermally disjunct water beetle taxa also occur here, including Microcylloepus moapus moapus (La Rivers, 1949c), and Stenelmis callida moapa (La Rivers, 1949b), the latter also occurring at Ash Warm Spring. Despite occasional collections by numerous specialists over the years, a comprehensive entomological inventory of this spring oasis has not yet been published. In addition to the taxa listed above, the thermal outflows in this area also support mosquitos in the Uranotaenja anhydor complex, the dragonfly Brechmorhoga mendax, and the mayflies lsonychja campestrjs, Leptohyphes apache, and Camelobaetidus salinus, all of which might also be considered thermal disjuncts. The general setting of this spring oasis was described Williams et al. (1985) , and the habitat partitioning exhibited by the naucorid species inhabiting it was discussed by La Rivers (1950).

Amargosa River

The Amargosa River heads in the Bullfrog Hills of Nevada, flowing southward for over 1 00 miles before hooking abruptly back to the north and emptying into the sink of Death Valley. Like the White River, the Amargosa is a dessicated drainage that retains permanent flow only in a few isolated sections. The major thermal spring oases in the Amargosa system occur along the middle section along a former at Ash Meadows, on the lower middle section of the river at Tecopa, Shoshone and Besting springs, and along the terminal reach of the drainage at Saratoga Spring in Death Valley. In addition, other significant concentrations of thermal springs occur at and near Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 15

Furnace Creek in the middle section of Death Valley, and at Grapevine Springs near the valley's northern end, along what would formerly have been tributaries to the main river. The locations of these oases are detailed in figure 1. · The Amargosa Basin is the most isolated of the three basins under discussion, and also contains the richest concentration of endemic and disjunct aquatic Hemiptera. Lying in the lowest and hottest section of the North American continent, the basin undoubtedly retained a warm climate even during the Pleistocene, which, combined with the presence of constant temperature thermal springs, allowed for the survival of a relict warm water entomofauna. The largest concentration of thermal springs in the Amargosa system is fou nd at Ash Meadows, where a complex of thirty seeps a springs support a remarkable assemblage of endemic plants, fish and insects. The springs of Ash Meadows form three discrete groups altitudinally and biologically. The highest of the springs in the area is Devils Hole, which contains an endemic pupfish and the endemic beetle Stenelmjs calljda calljda (Chandler, 1949) but apparently no aquatic Heteroptera. A second complex of springs lying at a slightly lower elevation, including North Scruggs, South Scruggs, North Indian, South Indian, Marsh and School springs, supports an undescribed and endemic Ambrysus species (Polhemus and Polhemus, in press). Many of these springs also harbor thermally disjunct popu lations of Belostoma saratogae and Pelocorjs shoshone (see table 1). The lowest elevation set of springs contains numerous large thermal outflows, including Point of Rock Springs, which is the sole habitat for the endemic Ambrysus amargosus; the habitat preferences of this species were described in detail by La Rivers (1953). Many of the larger springs in Ash Meadows, including Point of Rock, were extensively modified in past decades to support planned agricultural and residential developments. As a result, Ambrysus amargosus has been driven nearly to the point of extinction (D. Polhemus, in press), being currently classified as threatened under the Endangered Species Act, and the disjunct populations of Bhagoyelja distincta and Pelocoris shoshone that formerly occured at Point of Rock have been extirpated. The thermal springs of the middle Amargosa River are concentrated at the towns of Shoshone and Tecopa, and at the the nearby ranch at Resting Springs. All have suffered from human disturbances associated with municipal, recreational, or agricultural development. Access to Resting Spring, which lies of private land, is currently restricted by the ranch owner. The spring head has reportedly been capped, and the outflow piped, which if true would likely have extirpated any aquatic Hemiptera species that formerly inhabited the spring. The only known record of aquatic Hemiptera from the site is a collection of the riffle bug Rhagovelia distjncta made in 1956. This species is widespread in the outside of the Great Basin, but occurs only as extremely localized populations at isolated thermal refugia within the basin itself (see previous discussion concerning this species in the White River system). All known localities for Rhagoyelia in the southern Great Basin also harbor other thermal disjuncts, thus its presence at Resting Spring indicates that this site also once supported a diverse aquatic Hemiptera assemblage, likely including thermal endemics or disjuncts. The springs at Tecopa, a few miles west of Resting Spring, are the hottest in the Amargosa system, having an emergent temperature of 43 o C. (109° F.), and formerly supported an endemic pupfish subspecies, which is now extinct. Pools near the spring heads at this site formerly supported extremely large concentrations of Pelocorjs shoshone, but this habitat appears to have been completely eliminated in the course of development for recreational . Other less disturbed thermal outflows still occur to the north of the Tecopa Hot Springs resort along the paved highway between Shoshone and Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 16

Tecopa, and these habitats still support both Pelocorjs and Belostoma, although the occurrence of the latter appears to be seasonal (D. Threloff, pers. comm.). The thermal spring at Shoshone has similarly been modified for municipal use, with the spring head boxed and the outflow creek mostly piped to supply a local . A small section of somewhat natural habitat remains between the spring head and the pipe collector system, consisting of a deep pond and a short stretch of flowing channel. The pond supports a population of Pelocorjs shoshone, and the flowing channel contains Ambrysus mormon. These two species are likely to persist at this locality if no further alterations to the habitat are made, but overall the spring fauna a Shoshone must be considered at risk. Along the lower Amargosa River, the most notable thermal refugium occurs at Saratoga Spring, a very large thermal outflow that emerges at the base of the Ibex Hills, near the extreme southern end of Death Valley; this spring habitat was described in detail by Belkin and McDonald (1956). The aquatic Hemiptera fauna of the spring is unique and distinctive, including a highly disjunct population of the giant water bug Lethocerus angustipes, which is otherwise not known outside of central Mexico. Other disjunct species here include Pelocoris shoshone, Belostoma saratogae (for which this is the type locality), Nerthra martini, and Hydrometra australis (see Table 1). Other interesting aquatic insects here include a disjunct population of metallic-colored mosquitos in the Uranotaenja anhydor complex (Belkin and McDonald, 1956). Despite a long history of human use, the habitat at Saratoga Spring is in good condition, and all of its known aquatic Hemiptera species were recollected during a survey in July 1993. The location of the spring within the Death Valley National Monument should insure the continued survival of this unique desert ecosystem. · A second focus of endemism in the lower Amargosa is found along the course of Furnace Creek, next to the main entrance "highway to the national monument. The thermal outflows concentrated in this area, most notably Travertine, Cow Creek, and springs, harbor the endemic naucorid Ambrysus funebrjs, and a disjunct population of Nerthra martini. Although the spring outflow at Travertine has been diverted into a concrete adjacent to the road, this seems to have provided an excellent artificial habitat for A. funebris, which occurs there in large numbers. The continued existence of this species is likely to be insured in the near term due to the location of all its known habitats within the national monument, even though not all of the springs it occupies are in a natural state. The spring habitat at Cow Creek was described in detail by La Rivers (1948, 1951 ). The most significant thermal refugium in northern Death Valley is found at Grapevine Springs, consisting of many small thermal outflows perched on a bench above the valley floor to the northeast of Stovepipe Wells. The outflow channels in this area are for the most part heavily overgrown, and thus difficult to sample. At a few spots the waters have pooled to form small ponds which support populations of Pelocoris shoshone, this being the most northerly occurrence of this species in California. The overall habitat here is in good condition, although many of the spring heads are covered by introduced palms and other encroaching vegetation, and thus do not present an original aspect. Similar outflows once occurred along the bed of Grapevine Creek, in Grapevine Canyon to the east, but these were extensively altered and diverted over the last hundred years to supply the small settlement at Scotty's Castle, and as a result do not appear to retain any of their former thermally dependant aquatic Hemiptera species. .. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 1 7

BIOGEOGRAPHIC SUMMARY

Based on the distributions of disjunct aquatic Hemiptera populations in thermal springs, it appears likely that Railroad Valley, the White River, and the Amargosa River all formed portions of a single united drainage network at some time in the past. This system was subsequently fragmented by geological rifting involved with the ongoing extension of the Great Basin, causing Railroad Valley and the Amargosa system to become isolated endorheic basins. The continuing development of the present Colorado and Virgin rivers has also altered drainage patterns in the region, causing the White River to connect more directly into the Colorado system rather than joining with the Amargosa, as it appears to have done in the past. The exact sequence of isolation events is not at all certain, and may be difficult to deduce based on the cladistics of the aquatic Hemiptera species involved, since the populations in the various spring refugia, though profoundly isolated, have in most cases not undergone extensive morphological differentiation. In any event, the taxonomic status of the Pelocorjs and Belostoma populations in these three basins will have to be resolved before any specific biogeographic hypotheses can be critically evaluated. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 18

LITERATURE CITED

Belkin, J. N. and W. A. McDonald. 1956. A population of Uranotaenja anhydor from Death Valley, with descriptions of all stages and discussion of the complex (Diptera, Culicidae}. Ann . Entomol. Soc. Amer., 49: 105-131.

Chandler, H. P. 1949. A new species of Stenel,miS from Nevada (Coleoptera, Elmidae) . Pan-Pac. Entomol., 25 {3): 133-136.

Deacon, J. E. and J. E. Williams. 1984. Annotated list of the fishes of Nevada. Proc. Bioi. Soc. Wash., 97: 103-118.

De Carlo, J. A. 1951. Genera Limnocoris StAI. Misi6n Est. Patalogia Reg. , 22 : 41-51.

Echelle, A. A. and T. E. Dowling. 1992. Mitochondrial DNA variation and evolution of the Death Valley pupfishes (Cyprjnodon, Cyprinodontidae}. Evolution, 46 {1 }: 193-206.

Garside, L. J., and J . H. Schilling. 1979. Thermal waters of Nevada. Nevada Bureau of Mines and Geology Bull., 91 . 163 pp.

Guerin-M eneville, F. E. 1857. Ordre des Hemipteres, Latr. Premiere section. Heteropteres, Latr. in M. R. Sagra's Historie Physique, Politique et Naturelle de l'lle Cuba. Arthus Bertrand, Paris. 7: 359-424.

Hershler, R. and W. L. Pratt. 1990. A new Pyrgulopsjs (Gastropoda: Hydrobiidae} from southeastern California, with a model for historical development of the Death Valley hydrographic system. Proc. Bioi. Soc. Wash., 103 (2}: 279-299.

Hubbs, C. L. and R. R. Miller. 1948a. Two new relict genera of cyprinid fishes from Nevada. Occ. Papers Mus. Zool. Univ. Mich., No. 507: 1-30.

Hubbs, C. L. and R. R. Miller. 1948b. The zoological evidence: correlation between fish distribution and hydrographic history in the desert basins of western United States, pp. 18-166 in The Great Basin, with Emphasis on Glacial and Postglacial Times. Bull. Univ. of Utah, 38 (20). 191 pp.

Hungerford, H. B. The genus Notonecta of the world. Bull. Univ. Kansas, 34 (5}: 5- 195.

La Rivers, I. 1948. A new species of Ambrysus from Death Valley, with notes on the genus in the United States (Hemiptera: Naucoridae). Bull. So. Calif. Acad. Sci., 47 (3): 103-110.

La Rivers, I. 1949a. A new species of Pelocorjs from Nevada, with notes on the genus in the United States (Hemiptera: Naucoridae). Ann. Entomol. Soc. Wash., 41 (3) : 371-376 . Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 1 9

La Rivers, I. 1949b. A new subspecies of Stenelmjs from Nevada (Coleoptera: Dryopidae). Proc. Entomol. Soc. Wash., 51: 218-224.

La Rivers, I. 1949c. A new species of Microcylloepus from Nevada (Coleoptera: Dryopidae). Ent. News, 60: 205-209.

La Rivers, I. 1950. The meeting point of Ambrysus and Pelocorjs in Nevada (Hemiptera: Naucoridae). Pan-Pac. Entomol., 26 (1 ): 19-21.

La Rivers, I. 1950. A new naucorid genus and species from Nevada (Hemiptera). Ann. Entomol. Soc. Amer., 43: 368-373.

La Rivers, I. 1951 . A revision of the genus Ambrysus in the United States (Hemiptera: Na,ucoridae). Univ. Calif. Pub. Entomol., 8 (7): 277-338.

La Rivers, I. 1953. New gelastocorid and naucorid records and miscellaneous notes, with a description of the new species, Ambrysus amargosus (Hemiptera: Naucoridae). Wasmann J. Bioi., 11 (1 ): 83-96.

La Rivers, I. 1956. A new subspecies of Pelocorjs shoshone from the Death Valley drainage (Naucoridae: Hemiptera). Wassmann J. Bioi., 14 (1) : 155-158.

La Rivers, I. 1963. Two new ambrysi (Hemiptera: Naucoridae). Bioi. Soc. Nevada Occ. Papers, 1: 1-7.

Lauck, D. R. 1964. A monograph of the genus Belostoma. Part Ill. E.. triangulum, .b..e..r.CJ.i, m..inQr, bifoveolatum, and flumineum groups. Bull. Chicago Acad. Sci., 11: 102- 154.

Menke, A. S. 1958. A synopsis of the genus Belostoma Latrielle of America north of Mexico, with the description of a new species. Bull. So. Cal. Acad. Sci., 57: 154- 171.

Menke, A. S. 1979. Family Belostomatidae/giant water bugs, electric light bugs, toe biters, pp. 76-86 i..o. The Semiaquatic and Aquatic Hemiptera of California (Heteroptera: Hemiptera). Bull. Calif. Insect Survey, 21 : xi+ 166 pp.

Menke, A. S. 1979. Family Gelastocoridae/toad bugs, pp. 126-130 i..o. The Semiaquatic and Aquatic Hemiptera of California (Heteroptera: Hemiptera). Bull. Calif. I nsect Survey, 21 : xi+ 166 pp.

Montandon, A. L. 1898. Hemiptera cryptocerata. Notes et descriptions de especes nouvelles. Bulletin de Ia Societe des Sciences de Bucarest-Roumanie, 7: 282- 290.

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Montandon, A. L. 1910. Hydrocorises de !'Amerique du Nord. Notes et descriptions d'especes nouvelles. Bulletin de Ia Societe des Sciences de Bucarest-Roumanie, 18: 180-191 . Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 20

Polhemus, D. A. In press. Conservation of aquatic insects: worldwide crisis or localized threats? Amer. Zool.

Polhemus, J. T. 1973. Notes on aquatic and semiaquatic Hemiptera from the southwestern United States (Insecta: Hemiptera). Great Basin Nat., 33 (2): 1 13-119. '

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Polhemus, J. T. and H. C. Chapman. 1979. Family Saldidae/shore bugs, pp. 16-33 in The Semiaquatic and Aquatic Hemiptera of California (Heteroptera: Hemiptera). Bull. Calif. Insect Survey, 21 : xi+ 166 pp.

Polhemus, J. T. and H. C. Chapman. 1979. Family Mesoveliidae/water treaders, pp. 39-42 in The Semiaquatic and Aquatic Hemiptera of California (Heteroptera: Hemiptera). Bull. Calif. Insect Survey, 21: xi+ 166 pp.

Polhemus, J. T. and H. C. Chapman. 1979. Family Hydrometridae/marsh treaders, pp. 43-45 .in The Semiaquatic and Aquatic Hemiptera of California (Heteroptera: Hemiptera). Bull. Calif. Insect Survey, 21 : xi+ 166 pp.

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Williams, J. E., D. B. Bowman, J. E. Brroks, A. A. Echelle, R. J. Edwards, D. A. Hendrickson, and J. J. Landye. 1985. Endangered aquatic ecosystems in North American deserts with a list of vanishing fishes of the region. J. Arizona-Nevada Acad. Sci., 20: 1-62. Polhemus and Polhemus: Aquatic Hemiptera of Desert Hot Springs 21

Figure Legend

Figure 1: Southern Great Basin, showing locations of major spring refugia discussed in this report. Open circles = cold springs, dots = thermal springs. Arrows show potential former hydrologic connections between presently isolated basins. For further details see text. 1 = Duckwater 2 = Locke's Ranch 3 = Upper White River 4 = Middle White River (Pahranagat Valley) 5 = Moapa Warm Springs 6 = Ash Meadows 7 = Middle Amargosa River (Shoshone, Tecopa) 8 = Saratoga Spring 9 = Furnace Creek 10 = Grapevine Springs NEVADA

' I I '' I ' I ' I Area ' I '0 I, of 0 0' ' ' I Sterile .' , White ., Basins ' River ''

',0' ,· ' I Amargosa i River :'

,'' ,.,~ - - / ,' •... ' , .. CALIFORNIA , : · 6 ~~ t ...... ' •,\

.I 0 '

Southern Great Basin showing locations of thermal spring refugia

drainage