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Inventory of three beetle species assemblages (Coleoptera: Carabidae, Scarabaeoidea, Tenebrionoidea) from the Chihuahuan Desert of west Texas.

Abstract. -- Pitfall traps were used to study the abundance and diversity of three species assemblages of Coleoptera from four proximal sites in the Chihuahuan Desert of the Trans-Pecos region of west Texas. Members of the family Carabidae and superfamilies Scarabaeoidea and Tenebrionoidea were collected from four ecological habitats from September 1999 to September 2000. A total of 994 individuals, representing 53 species of beetles, was collected over the duration of the survey. The tenebrionoids were the dominant assemblage collected, and were only outnumbered by the scarabaeoids at one collecting site (Lower Spring). Carabidae was the least abundant of the three assemblages. The four localities yielded relatively equivalent collections of individuals, yet Camp Site was the least taxonomically diverse and exhibited a beetle fauna consisting primarily of tenebrionoids. Collection sites with water to support a more diverse flora (Sandy Canyon and Upper Spring) also supported a more diverse beetle fauna. This study provides a baseline for continuing arthropod investigations of the desert habitats of the Dalquest Research Site in west Texas.

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The order Coleoptera is the largest and most diverse assemblage of insects (Rieske & Buss 2001). The sheer numbers and taxonomic diversity of beetles commonly dictate that most beetle studies are either restricted geographically or focus on a limited number of families (Arnett & Thomas 2001). Only two works are available that emphasize Chihuahuan Desert beetles of the Trans-Pecos region: a comprehensive study of beetles from a sand dune in Big Bend National Park (Dajoz 2000); and a community assessment of carrion arthropods (Schoenly & Reid 1983). However, beetles comprise an important part of the Chihuahuan Desert arthropod fauna, and have proven to be useful environmental indicators of the region, documenting climatic shifts from the late Pleistocene through Holocene times (Elias & Van Devender 1990).

Pitfall trapping has long been an acceptable method of collecting terrestrial arthropods (Ahearn 1971; Reiske & Buss 2001), in spite of a confounding array of potential biases (Briggs 1960; Thomas & Sleeper 1977; Spence & Niemela 1994; Ward et al. 2001). Nevertheless, this technique provides the opportunity for continuous sampling where the objectives are to generate faunal inventories and to permit assemblage comparisons (Faragalla & Adam 1985).

In 1996, the late Walter W. Dalquest and wife Rose donated 518 ha of land to Midwestern State University for the purpose of fostering biological research. Designated the Dalquest Research Site (DRS), the property straddles the Brewster/Presidio County line and extends along the northern boundary of Big Bend Ranch State Park (Fig. 1). The area is an interface between Bandera Mesa and a rift valley of heavily eroded canyon lands that shelter isolated seeps, springs, and intermittent streams. Vegetation is typical desert scrub, although plant growth is comparatively lush near water sources.

This study stems from an earlier assessment of cursorial spiders at the Dalquest Research Site (Broussard & Horner 2006). This study reports the results of a year of continuous pitfall sampling of beetle diversity from four ecologically diverse sites, emphasizing the three most prominent coleopteran assemblages present: Carabidae (ground beetles and tiger beetles); Scarabaeoidea (June beetles, dung beetles, and related forms) and Tenebrionoidea (darkling beetles and allies).

STUDY SITE

Four collection localities were selected on the basis of variation in substrate, water availability, and resident vegetation. Three sites were selected from the comparatively heavily vegetated depths of the canyons, and one site was selected as representing the desert scrub dominating the mesa and surrounding level terrain.

The first locality (Camp Site; 29[degrees] 33.408' N, 103[degrees] 47.648' W; elevation 1,267 m) is desert hardpan with shallow rocky soils and exposed bedrock, situated at the fault rim. Terrain is gently rolling and dominated by creosote (Larrea tridentata (Sesse & Moc. ex DC.) Coville), lecheguilla (Agave lechuguilla Torr.), and cacti (Opuntia spp.). Vegetation seldom exceeds 1 m in height. This area serves as camp headquarters for field investigators and is the most heavily impacted of all selected sites by human activity, although disturbance is minimal.

[FIGURE 1 OMITTED]

The second site (Sandy Canyon; 29[degrees] 33.130' N, 103[degrees] 47.600' W; elevation 1,212 m) is situated about 400 m south of Camp Site and derives its name from the sandy flood plain of an intermittent stream, the Alamo de Ceserio. Woody vegetation includes mesquite (Prosopis glandulosa Torr.), little walnut (Juglans microcarpa Berl.), allthorn (Koeberlinia spinosa Zucc.), agerito (Berberis trifoliata Moric.), and oak (Quercus spp.). Clump grasses and leaf litter contribute to the habitat.

Two other sites less than 900 m to the west in sheltered canyon bottoms were also selected. One of these (Lower Spring; 29[degrees] 33.391' N, 103[degrees] 47.133' W; elevation 1,148 m) is sparsely vegetated due to occasional flooding, with a few scattered creosote shrubs. Soils are of fine silts and sediments resulting from outflow of the stream. The fourth site (Upper Spring; 29[degrees] 33.165' N, 103[degrees] 47.151' W; elevation 1,150 m) is approximately 400 m upstream from Lower Spring. Soils are primarily sands and fine clay that support the most diverse and dense flora of the study area. The most conspicuous elements are a mesquite-oak woodland that includes catclaw mimosa (Mimosa biuncifera Benth.), yucca (Yucca faxoniana (Trel.) Sarg.), desert sumac (Rhus microphylla Engelm. ex Gray), ocotillo (Fouquieria splendens Engelm.), graythorn lotebush (Ziziphus obtusifolia (Hook. ex Torr. & Gray) Gray), and beargrass (Nolina erumpens (Torr.) Wats.).

MATERIALS AND METHODS

Ten pitfall traps with 10 cm-diameter mouths were placed at each of the four sites in early September 1999. Each trap consisted of two one-liter plastic cups, one inside the other, and buried with tops flush with the ground surface. Each was partially filled with propylene glycol solution (commercially available low-toxicity antifreeze) to serve as a killing agent and preservative. Pitfall traps were separated by approximately 9 m, arranged in grids where terrain permitted, or placed in linear transects where necessary.

The survey period extended until 15 September 2000, with three 1999 collection dates (7 October, 11 November, and 9 December) and five dates in 2000 (7 January, 24 February, 19 May, 6 July, and 15 September). Collecting effort was recorded as trap nights, which are calculated as follows: number of pitfall traps times number of collection sites times number of collecting dates. On each collecting date, pitfall trap contents were returned to the laboratory at Midwestern State University for identification. Members of the Carabidae, Scarabaeoidea (Scarabaeidae, Hybosoridae, Trogidae), and Tenebrionoidea (Tenebrionidae, Zopheridae) were sorted and identified to genus based primarily on the keys of Arnett & Thomas (2001) and Arnett et al. (2002) and, where possible, to species or morphospecies by specimen comparison and/or specialist confirmation. For purposes of discussion, individual species were categorized as "abundant" (n[greater than or equal to]75), "common" (n=30-74), "uncommon" (n=10-29), and "rare" or of "incidental occurrence" (n=1-9).

Assessment of seasonal availability was accomplished by pooling collections into three temporal samples: a period roughly equating to the fall and early winter months (4 September to 9 December, 1999); an interval encompassing the late winter and spring months (10 December, 1999 to 18 May, 2000), and the duration of the study that included the summer months (19 May to 14 September, 2000). All specimens were pinned or point-mounted and are deposited in the invertebrate collection of the Department of Biology, Midwestern State University.

RESULTS

A total of 15,070 trap nights collectively produced 994 adult specimens (Table 1) of the family Carabidae (11 genera, 14 species), and superfamilies Scarabaeoidea (8 genera and 13 species of Scarabaeidae; one species of Hybosoridae; 2 genera and four species of Trogidae) and Tenebrionoidea (14 genera and 20 species of Tenebrionidae; one species of Zopheridae). The dominant family was the Tenebrionidae, which comprised nearly half of all beetles taken, and which was well represented throughout the year at each of the sites (Table 2). Only at the Lower Spring did another assemblage (Scarabaeoidea) outnumber the tenebrionoids at any of the four collection sites during the duration of the study (Table 1). Members of the Scarabaeoidea comprised 31.3 % of the sample, and were most commonly taken during the fall period of 4 September-9 December. Carabidae was the most poorly represented taxon of the three species assemblages at 18.5 %, with more than half of the specimens collected from the interval of 19 May to 14 September.

Each of the four collection localities yielded comparable collections numerically, although the three canyon collections were more diverse taxonomically (Fig. 2). Camp Site (n=212) supported 11 genera and species, with three tenebrionoid taxa comprising the majority of specimens. The majority of tenebrionoids (n=116) were taken from 10 December, 1999 to 18 May, 2000. Sandy Canyon (n=286) supported 23 genera and 33 species, with comparable representation of the three species assemblages. Lower Spring (n=292), with 18 genera and 20 species, supported mostly scarabaeoid taxa, although tenebrionoid beetles were well represented. Scarabaeoids were least common of beetles at Upper Spring (n=204), with 22 genera and 26 species recorded.

DISCUSSION

Most of the beetles included in this study are essentially terrestrial "ground" beetles. While many of these taxa are certainly capable of flight, few probably exercise this dispersal ability to any great extent. Life histories of most member species of these beetle assemblages are imperfectly known, although generalizations of the life histories of these groups have been advanced (Stehr 1991; Arnett & Thomas 2001; Arnett et al. 2002).

Carabid adults are active, cursorial foragers that opportunistically scavenge, browse tender vegetation, and hunt for invertebrate prey, while larvae are typically carnivorous, pursuing a variety of soft-bodied invertebrates procured from the cover of rocks, rotted logs, and in leaf litter. Adult scarabaeoid beetles are typically either phytophagous or saprophagous. The scarabaeiform, or grub-like, larvae of some taxa feed on plant roots, and both adult and immature stages of others feed on the dung of mammals. Flight is probably more common among species of this assemblage. The adult stage of some species is short-lived. Tenebrionoids are typically long-lived, nocturnal beetles that include a number of desert specialists. Species commonly are commensal inhabitants of rodent burrows or the nests of other insects and birds. Adults are primarily fungivores or are saprophagous and larvae feed on dead and decaying plant matter ranging from wood to humus.

[FIGURE 2 OMITTED]

Most of the beetle taxa identified in this study can be classified as either rare and resident or as incidental in occurrence and not necessarily indicative of resident populations at the chosen research sites. Of the five taxa found at each of the four sites, perhaps only Eleodes sp. 2 occurred in sufficient numbers to be considered truly ubiquitous throughout the study area--from the creosote flats to the canyon depths. Each of the canyon sites supported unique beetle species (Lower Spring, n=6; Upper Spring, n=7; Sandy Canyon, n=14), possibly reflecting the low vagility of these animals and the effectiveness of canyon walls as dispersal barriers.

The thin, rocky soils and exposed bedrock of the Camp Site locality that support little more than creosote and lecheguilla also support a primarily tenebrionoid beetle fauna comprised of three species, Eleodes sp. 2 and unconfirmed species of Trimytis and Triorophus. Dominance by the darkling beetles is attributed largely to their capability of utilizing the burrows of rodents, especially those of the locally common Merriam's kangaroo rat (Dipodomys merriami Mearns). These extensive labyrinths provide shelter, and the bedding, food stores, and feces probably afford suitable sustenance for both adults and larvae. Neither of the two species unique to Camp Site, Asidina furcata (Champion) and an unidentified tenebrionid, were large components of the survey and are most likely incidental collections.

Springs, streams, and a higher water table support a comparatively lush and diverse flora, and correspondingly diverse beetle fauna, in the canyon localities of Sandy Canyon and Upper Spring. Essentially serving as woodland refugia, these sites are dominated numerically by tenebrionids, although the stabilized soils and accumulated humus and leaf litter contribute to habitats capable of supporting a great taxonomic array of carabids and scarabaeoids at all life stages. In contrast, regular scouring of the Lower Spring site by flood waters prevents establishment of a more diverse plant community, while probably also simultaneously purging the resident invertebrate populations. While the beetle fauna at this locality possessed the least diversity of the three canyon sites, it is notable that the dung beetle, Canthon imitator Brown, which was present at each of the canyon sites, was present at Lower Spring in greater numbers than any other beetle species at any locality. Most of these records came from the first sampling period of 4 September-9 December, which was probably indicative of a single mass emergence. The scarab Ataenius desertus Horn and tenebrionid Argoporis rufipes nitida Casey occurred in numbers only at Upper Spring and Lower Spring, respectively, and we speculate that the fecal waste of larger mammals (e.g., javelina, Tayassu tajacu (L.); mule deer, Odocoileus hemionus (Rafinesque)) frequenting the water source is a locally important nutrition source.

FUTURE STUDIES

This faunal study provides a baseline inventory for long-term investigation of the biology of three prominent coleopteran components of Chihuahuan Desert habitats on the Dalquest Research Site. Planned efforts include an assessment of less common beetle taxa, and collections of free-ranging beetle larvae to distinguish between resident and transient species of carabids, scarabaeoids, and tenebrionoids. Monitoring of these taxa is ongoing, and the recent installation of a weather-recording station by Midwestern State University will help determine species with potential as environmental indicators.

ACKNOWLEDGMENTS

Financial support for the fieldwork was provided by Midwestern State University, the late Walter W. Dalquest, and wife, Rose. We thank Ed Riley of Texas A & M University, James Cokendolpher of Texas Tech University, and Norman Horner of Midwestern State University for their critical assistance in the identification of problematic taxa. William Cook of Midwestern State University kindly identified components of the local flora. Frederick Stangl contributed meaningful insight into presentation of data and the manuscript.

LITERATURE CITED

Ahearn, G. A. 1971. Ecological factors affecting population sampling of desert tenebrionid beetles. Am. Midl. Nat., 86(2):385-406.

Arnett, R. H. & M. C. Thomas, eds. 2001. American Beetles. Vol. 1. Archostemata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia. CRC Press, Boca Raton, Florida, 443 pp.

Arnett, R. H., M. C. Thomas, P. E. Skelley & J. H. Frank, eds. 2002. American Beetles. Vol. 2. Polyphaga: Scarabaeoidea through Curculionoidea. CRC Press, Boca Raton, Florida, 861 pp.

Briggs, J. B. 1960. A comparison of pitfall trapping and soil sampling in assessing populations of two species of ground beetle (Carabidae). East Malling Res. Stn. Ann. Rep., 48:108-112.

Broussard, G. H. & N. V. Horner. 2006. Cursorial spiders (Arachnida: Araneae) in the Chihuahuan Desert of western Texas, USA. Entomol. News, 117(3):249-260.

Dajoz, R. 2000. Les Coleopteres d'une du Big Bend National Park (Texas). Nouv. Rev. Entomol., 17(4):355-363.

Elias, S. A. & T. R. Van Devender. 1990. Fossil Insect Evidence for Late Quaternary Climatic Change in the Big Bend Region, Chihuahuan Desert, Texas. Quat. Res., 34:249-261.

Faragalla, A. A. & E. E. Adam. 1985. Pitfall trapping of tenebrionid and carabid beetles (Coleoptera) in different habitats of the central region of Saudi Arabia. Z. Angew. Entomol., 99(5):466-471.

Rieske, L. K. & L. J. Buss. 2001. Influence on diversity and abundance of ground- and litter-dwelling Coleoptera in Appalachian Oak-Hickory forests. Environ. Entomol., 30(3):484-494.

Schoenly, K. & W. Reid. 1983. Community structure of carrion arthropods in the Chihuahuan Desert. J. Arid Environ., 6(3):253-263.

Spence, J. R. & J. Niemela. 1994. Sampling carabid assemblages with pitfall traps: the madness and the method. Can. Entomol., 126(3):881-894.

Stehr, F. W., ed. 1991. Immature Insects, Vol. 2. Kendall/Hunt Publ. Co., Dubuque, Iowa, xvi + 975 pp.

Thomas, D. B. & E. L. Sleeper. 1977. The use of pit-fall traps for estimating the abundance of arthropods with special reference to the Tenebrionidae. Ann. Entomol. Soc. Am., 70(2):242-248.

Ward, D. F., T. R. New & A. L. Yen. 2001. Effects of pitfall trap spacing on the abundance, richness and composition of invertebrate catches. J. Insect Conserv., 5(1):47-53.

SMM at: michael.shipley@mwsu.edu

Stephanie M. Middleton, Greg H. Broussard*, Michael M. Shipley and Roy C. Vogtsberger

Department of Biology, Midwestern State University

Wichita Falls, Texas 76308

*Current address

Department of Entomology, Oklahoma State University, Stillwater, Oklahoma 74078
Table 1. Species composition of three species assemblages of Coleoptera
collected by pitfall trapping at Dalquest Research Site, from September
1999 through September 2000.

 Camp Sandy Lower Upper
Taxon Site Canyon Spring Spring Subtotal

Carabidae
 Amara sp 0 0 0 1 1
 Apenes sp. 1 0 33 0 61 94
 Apenes sp. 2 0 1 0 0 1
 Calosoma affine Chaudoir 0 1 0 0 1
 Calosoma parvicolle Fall 0 1 0 1 2
 Cymindis sp. 0 11 0 9 20
 Helluomorphoides sp. 0 2 0 0 2
 Microlestes sp. 2 0 3 0 5
 Pasimachus sp. 1 41 4 3 49
 Pentagonica sp. 0 0 0 1 1
 Poecilus sp. 0 0 1 0 1
 Selenophorus sp. 1 0 1 0 0 1
 Selenophorus sp. 2 0 3 0 0 3
 Tetragonoderus intersectus 0 2 0 1 3
 (Germar)
Subtotal 3 96 8 77 184

Scarabaeoidea
Scarabaeidae
 Ataenius convexus Robinson 0 1 0 23 24
 Ataenius desertus Horn 0 0 31 0 31
 Ataenius sp. 0 0 1 1 2
 Canthon imitator Brown 0 10 134 2 146
 Diplotaxis brevicornis Cazier 0 1 0 0 1
 Diplotaxis sp. 1 0 1 0 0 1
 Diplotaxis sp. 2 0 1 0 0 1
 Diplotaxis subangulata 0 1 0 0 1
 LeConte
 Euoniticellus intermedius 0 0 3 1 4
 (Reiche)
 Onthophagus velutinus Horn 0 2 0 0 2
 Oxygrylius ruginasus 0 0 1 0 1
 (LeConte)
 Phyllophaga pusillidens Fall 0 0 3 0 3
 Serica porcula Casey 0 4 0 8 12
Hybosoridae
 Hybosorus illigeri Reiche 0 0 3 0 3
Trogidae
 Omorgus inflatus (Loomis) 0 1 1 0 2
 Omorgus punctatus (Germar) 2 47 22 3 74
 or O. inflatus (Loomis)
 Omorgus suberosus (Fabricius) 0 0 0 1 1
 Trox spinulosus Robinson 0 0 0 2 2
Subtotal 2 69 199 41 311

Tenebrionoidea
Tenebrionidae
 Argoporis rufipes nitida Casey 0 1 15 0 16
 Asbolus sp. 1 0 0 1 0 1
 Asbolus sp. 2 0 0 0 2 2
 Asidina furcata (Champion) 1 0 0 0 1
 Asidina paralella (LeConte) 0 0 0 2 2
 Blapstinus sp. 1 4 69 0 12 85
 Blapstinus sp. 2 0 1 0 20 21
 Blapstinus sp. 3 0 1 0 0 1
 Cryptoglossa infausta 0 0 7 11 18
 (LeConte) or C. texana
 Blaisdell
 Eleodes sp. 1 0 1 0 2 3
 Eleodes sp. 2 78 20 20 13 131
 Eupsophulus castaneus (Horn) 0 0 0 1 1
 Eusattus pons Triplehorn 0 1 0 0 1
 Helops sp. 0 1 0 0 1
 Megasida obliterata (Champion) 1 4 3 0 8
 or M. tenuicollis Triplehorn
 Platydema micans Zimmerman 0 2 0 0 2
 Hylocrinus sp./Steriphanus sp. 6 17 4 14 41
 Trimytis sp. 67 2 0 0 69
 Triorophus sp. 46 1 34 8 89
 Species undetermined 4 0 0 0 4
Zopheridae
 Zopherus championi Triplehorn 0 0 1 1 2
Subtotal 207 121 85 86 499
Total 212 286 292 204 994

Table 2. Seasonal availability of three species assemblages of
Coleoptera collected by pitfall trapping at Dalquest Research Site from
September 1999 through September 2000.

 Total Survey
 4 Sept.-9 10 Dec.-18 19 May-14 Period
 Dec. (3870 May (6440 Sept. (4760 (15,070 trap
Taxon trap nights*) trap nights) trap nights) nights)

Camp Site
Carabidae 1 1 1 3
Scarabaeoidea 0 1 1 2
Tenebrionoidea 34 116 57 207
Subtotal 35 118 59 212

Sandy Canyon
Carabidae 25 22 49 96
Scarabaeoidea 10 16 43 69
Tenebrionoidea 48 41 32 121
Subtotal 83 79 124 286

Lower Spring
Carabidae 2 3 35 40
Scarabaeoidea 127 34 6 167
Tenebrionoidea 27 28 30 85
Subtotal 156 65 71 292

Upper Spring
Carabidae 6 46 25 77
Scarabaeoidea 2 8 31 41
Tenebrionoidea 16 34 36 86
Subtotal 24 88 92 204

Assemblage Totals
Carabidae 34 72 110 216
Scarabaeoidea 139 59 81 279
Tenebrionoidea 125 219 155 499
TOTALS 298 350 346 994

*Total trap nights among all four collection sites.
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Author:Middleton, Stephanie M.; Broussard, Greg H.; Shipley, Michael M.; Vogtsberger, Roy C.
Publication:The Texas Journal of Science
Geographic Code:1U7TX
Date:Feb 1, 2007
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