A new species of tree cricket (Orthoptera, Gryllidae, Oecanthinae) from Chihuahuan Desert gypsum dunes in the United States and a key to the nigricornis species group

A new species of tree crickets, Oecanthus beameri sp. nov., is described from the gypsum dunes of White Sands National Park in New Mexico, United States. The new species is currently known only from the type local- ity, where it appears to be specific to the gypsophile plant hoary rosemary mint ( Poliomintha incana) . This new species has the narrowed tegmina and calling song that are found in the nigricornis species group. Although it has morphological similarities to O. quadripunctatus and O. celerinictus , there are differences in the subgenital plates, tegminal measurements, coloring, tibial markings, song frequency, and song pulse rate. This new species has been given the common name White Sands tree cricket. We provide a key to all species in the nigricornis group. Video and song recordings are available online as Suppl. materials 1–8.


Introduction
Two genera of Oecanthinae occur in the United States-Oecanthus Serville, 1831and Neoxabea Kirby, 1906(Cigliano et al. 2021; Singing Insects of North America (SINA) website (2021a)). Twenty-two of the species of Oecanthus in North America, Central America, and the Caribbean are divided into four main species groups: nigricornis, niveus, varicornis, and rileyi (Walker 1962, 1963, Walker and Collins 2010, Singing Insects of North America 2021b). These groups can be distinguished by characteristics including song type (chirping vs trilling and continuous vs intermittent); regular vs irregular pattern of pulses or chirps; coloration of the antennae, head, pronotum, and abdomen; antennal markings on the pedicel and scape; and tegminal width (Fulton 1915, Walker 1962, 1963, Walker and Collins 2010. All nine species in the nigricornis species group occur in North America: O. argentinus Saussure, 1874;O. celerinictus Walker, 1963;O. forbesi Titus, 1903;O. laricis Walker, 1963;O. nigricornis Walker, 1869;O. pini Beutenmüller, 1894;O. quadripunctatus Beutenmüller, 1894;O. salvii Collins, 2020;and O. walkeri Collins & Symes, 2012. In 2019, two specimens examined in the collection at the Academy of Natural Sciences of Drexel University (ANSDU) led to this investigation of a new species of Oecanthus. Two male specimens (Fig. 1), collected by Raymond H. Beamer (University of Kansas) in 1932 (Suppl. material 1: Beamer 1932 expedition), were found in the drawer containing O. quadripunctatus, but were visibly smaller and paler than all other males in the drawer. Fig.  1A, B show these differences when side by side with a male O. quadripunctatus in the collection box. Upon closer inspection, one of the specimens could be seen to have markings similar to O. quadripunctatus, with the upper outer round mark on the scape very faint, but the vertical line appeared to have a slight interruption midway (Fig. 1C). O. quadripunctatus has a total of four (rarely two) marks on the first two antennal segments (Fulton 1915, Walker 1963. Of additional interest was the fact that both of the smaller male specimens were collected in White Sands of New Mexico. White Sands National Park (WSNP) lies within the Chihuahuan desert and is comprised of dunes of bright white gypsum crystals that support gypsophilic plants. Our investigation sought to determine whether these were O. quadripunctatus, but smaller and paler because of their habitat, versus a distinct and undescribed species. We conducted a special research and collecting trip to WSNP in September of 2021, with the cooperation of the National Park Service (White Sands National Park, Scientific Research and Collecting Permit# WHSA-2021-SCI-0010), to collect specimens, record songs, and evaluate the habitat characteristics of the potentially new Oecanthus. This article describes the new species of Oecanthus from White Sands National Park.

Materials and methods
Specimens.-Seven adult males and one adult female of Oecanthus were collected on dunes (Fig. 2) adjacent to the Interdune Boardwalk at the WSNP in New Mexico between 21h and 22h from three locations separated by less than 1300 meters. Sunset was 19h15, and the males started calling around 20h, peaking around 21h. All seven males were approximately 1 m above the ground surface, and the female was on the white sand (gypsum) surface at an oatmeal bait trail.
A new species of tree cricket (Orthoptera, Gryllidae, Oecanthinae) from Chihuahuan Desert gypsum dunes in the United States and a key to the nigricornis species group nancy collins 1 , DaviD c. lightfoot 2 Specimens were located by the calling song of the males and collected manually within two hours of dusk. One female was collected from an oatmeal trail laid on the sand surface at dusk among shrubs of Poliomintha incana Gray, 1870, with singing males. No other Oecanthus species were heard singing in the area. Four of the eight tree crickets were brought indoors, kept alive, and separated to be recorded, and then preserved in 91% ethyl alcohol for morphological studies. Photographs were made with Canon S5 IS and Canon SX70 cameras. Measurements of the alcoholpreserved specimens were made with a Fischer spindle ruler.
Pinned specimens were dried in a moisture-extracting refrigerator to preserve their delicate greenish-white color. Measurements of the dried specimens, including the holotype, were made with an American Optical binocular dissecting scope and ocular micrometer, with magnification ranging from 10X to 50X. Measurements of alcohol preserved (n=3) and dry pinned specimens (n=3) are presented here as ranges and individually in Suppl. material 2 due to the contraction of dry membranous and some sclerotized tissues of dry pinned specimens.
Genus determination was made with keys from Walker (1967) and SINA (2021a) and review of taxa of Oecanthus in the Orthoptera Species File (Cigliano et al. 2021). Along with coloration, body length, antennal markings, cerci length and shape, subgenital plate details, and the female ovipositor, the male characters considered for description included tegmina length and width, stridulatory file length and number of teeth, metanotal gland features, and internal genitalia (focused on copulatory blades).
The following measurements were made: body length (from the tip of the labrum to the apex of the subgenital plate), pronotum length (from anterior to posterior margin along midline), pronotum width (at the widest distal portion in dorsal view), tegminal length (from the thorax joining point to distal end of tegmina along midline), tegminal width (measured at the widest section of the tegmina at rest or the maximum width of the dorsal surface of each tegmen excluding the lateral folds), hind femur length, and cerci length. The male stridulatory file length was measured along the ventral surface of the left tegmen A1 vein (Desutter-Grandcolas et al. 2017), from the first tooth at the A1 vein file lobe, toward the lateral margin of the A1 vein, to the last lateral tooth of the file on the A1 vein. The female ovipositor was measured from the base (originating from the abdomen) to the distal tip. The dominant shrub in the area of collection was hoary rosemary mint, Poliomintha incana, which is a gypsophile with whitish-green leaves and stems and a very pronounced and unique aromatic fragrance from plant defense chemicals. Many singing males were heard in the area but were not collected, and all were exclusively singing from P. incana.
Calling song recording and analyses.-The thermometer was held at the location on the plants where the males were calling immediately after capture on site, and within 10 cm from the indoor containers.
Temperatures of the perch sites of the males singing from the shrubs on site were measured using a hand-held Taylor mercury thermometer. An Accu-rite digital thermometer and an Accu-rite mercury thermometer were used to measure the temperature of the captive singing males.
The male acoustic signals that were recorded in the field at the collection site were recorded using an I-phone 11 held approximately 0.5 m from each calling male. Captive males were recorded with a Canon SX20S that was tested for calibration by recording a reference time audio file with reference tones and comparing the results to the original file. The camera was kept at a distance of less than 10 cm from the individual. Three male tree crickets were kept in large glass vases with mesh tops for observation and recordings. Video recording of a singing male can be viewed in Suppl. material 3. Analyses of audio waveforms and spectrograms were made with the Raven Lite 2.0 program (Cornell Lab 2021b). Additional recordings (Suppl. material 4) from the Macaulay Library of Cornell Lab (2021a) and data from the Singing Insects of North America website (SINA 2021c) were used for the preparation of two graphs Journal of orthoptera research 2022, 31 (2) to compare song pulses per second vs temperature and carrier frequency vs temperature with species in the nigricornis group.   Fig. 5A; male: rounded end as in Fig. 5C) can be distinguished from O. quadripunctatus (female: deep narrow notch as in Fig. 5B; male: tapered to a rounded tip as in Fig. 5D). When next to each other, a male O. beameri sp. nov. has a lighter coloring and smaller proportion of tegmen width to abdomen width than a male O. quadripunctatus (Suppl. material 5). Oecanthus beameri sp. nov. lacks the dark black lines across the proximal portion of the hind tibiae that are very common on O. celerinictus, but faint lines can be present (Fig. 3F). The deep black setae on the hind femora of O. salvii (Collins and Schneider 2020) are not present in O. beameri sp. nov. See below for more detailed diagnostic information.

Taxonomy
Description.-Face, pronotum, abdomen, and wings pale greenishwhite ( Fig. 3A-D), color number 97 (Köhler 2012). Eye color pale green. Palpi pale whitish green. Tympanal membrane on fore tibiae whitish green. Tarsi, tibiae, and femora translucent pale mint green. Tibiae without black setae or lateral black lines. Cerci straight and translucent pale green. Scape and pedicel translucent whitish, and remainder of antennomeres translucent whitish. Ventral face of pedicel and scape each with black marks on pale whitish field (Fig. 3C). See examples of antennal marking variations in Fig. 4. Etymology.-Specific epithet in recognition of Raymond Beamer who collected the specimens in 1932 that were discovered in the ANSDU collection in 2019. The common name, White Sands tree cricket, is for the location where this species was discovered with high potential for endemism.
Male paratypes.-(n=6) Body length (mm) 10.8-13.3; tegminal length 8.5-9.8; tegminal width 3.3-3.9; pronotal length 2.2-2.4; distal pronotal width 1.8-2.2; hind femur length 8.5-9.8; cerci length 2.7-3.1; stridulatory file length (n=5) 1.2-1.5. Right tegminal stridulatory teeth (as in Fig. 6A) number (n=5) 45-49. Tegmina with veins as in Fig. 3A. Subgenital plate with a rounded end (Fig. 5C). Copulatory blades thin with a deep notch separating them fairly equal to the width of one blade (Fig. 6B, C), and a slight indentation at the medial side of the distal end of each blade (6D). The metanotal gland with a rounded triangular depression, bristles running horizontally across the upper edge of the cavity, and no posterior medial lobe (Fig. 6E). These key out and match the diagram in Walker and Gurney (1967) for a member of the nigricornis species group. As pointed out by Walker and Gurney (1967), species within a group are difficult to separate based on the metanotal gland.
Female paratype description.-(n=1) Latticed vein pattern on translucent greenish-white wings. Abdomen pale white (Fig. 3E). Body length 11.5 mm; pronotal length 2.0, distal pronotal width 2.0; hind femur length 7.0; cerci 4.5; ovipositor length 3.5. The tip of the ovipositor flared (Fig. 6F) and extending just beyond the tips of the cerci. Distal end of subgenital plate with a wide, shallow notch (Fig. 5A). The only female collected (Fig. 3E) was missing the distal ends of the wings, thus dorsal photos not included.
Oviposition.-The female mated while in captivity and oviposited approximately 24 times into stems of an undetermined species of sage in both nodal and internodal areas (Fig. 7A, B). Species in the varicornis and nigricornis groups of Oecanthus generally oviposit within the stem internodal areas, while species in the niveus group prefer to oviposit in the nodal areas (Fulton 1915). Photographs of some nigricornis species group members' oviposition marks can be viewed on the Orthoptera Species File website (Cigliano 2021), including O. quadripunctatus. It is unknown whether being in captivity affected the locations of oviposition by this O. beameri sp. nov. female.
Climate and habitat.-On the day the tree crickets were collected, daytime temperatures reached 32-37°C, and cooled off to 26-31°C in the evening. Males were calling exclusively on hoary rosemary mint, P. incana, and were generally restricted to the tops of the gypsum dunes.  Colors, patterns and morphology-The antennal markings of O. beameri sp. nov. can total two, three, or four, with the medial mark on the scape usually broken into two pieces (Figs 3C, 4A-C), while O. quadripunctatus has either two or four marks with the medial mark on the scape being a solid post (SINA 2021c). The male and female subgenital plates of O. beameri sp. nov. (male: rounded end as in Fig. 5C; female: wide shallow notch as in Fig. 5A) can be distinguished from O. quadripunctatus (male: tapered to a rounded tip as in Fig. 5D; female: deep narrow notch as in Fig. 5B). When next to each other, a male O. beameri sp. nov. has a lighter coloring and smaller proportion of tegmen width to abdomen width than a male O. quadripunctatus (Suppl. material 5). O. celerinictus always has a solid medial mark on the scape and never lacks the upper outer mark on the scape, which is never round. O. beameri sp. nov. lacks the dark black lines across the proximal portion of the hind tibiae that are very common on O. celerinictus, but faint lines can be present (Fig. 3F). The deep black setae on the hind femora of O. salvii (Collins and Schneider 2020) are not present in O. beameri sp. nov. The two antennal marks on the pedicel of O. walkeri (Collins and Symes 2012) touch, while the marks on O. beameri sp. nov. do not.
Song pulse patterns.-The O. beameri sp. nov. male calling song is a continuous trill, often lasting 5-9 seconds with pauses of similar lengths, which increases in rate as the ambient temperature rises (Figs 8, 9). Captive males often trilled for up to 30 seconds.
Recordings of O. beameri sp. nov. were made in the field and in captivity. An onsite recording can be heard in Suppl. material 6, and a captive song sample at a similar temperature can be heard in Suppl. material 7. Recording of side-by-side captive O. beameri sp. nov. and O. quadripunctatus males at 23.8°C can be heard in Suppl. material 8. Pulse rate and frequency graphs provide comparisons to other species with similarities in the nigricornis group (Figs 9, 10). Four species were not included due to never being totally pale mint green and having black, dark brown, rust, or mahogany color on the ventral surfaces of the abdominal tergites: O. forbesi, O. laricis, O. nigricornis, and O. pini. Dichotomous key for the nigricornis species group-Since O. beameri sp. nov., O. celerinictus, and O. quadripunctatus are members of the nigricornis species group, it is not unexpected that no profound differences were evident in the following characters: number of stridulatory teeth number, tegmen configuration, and metanotal gland. The similarities of metanotal glands among species in the nigricornis species group can be viewed in Collins and Schneider (2020). The antennal markings of O. beameri sp. nov. can match (Fig. 4D)        The known members of the niveus, rileyi, and varicornis species groups can be ruled out with non-matching song types, tegminal widths, antennal markings, or head and antennal coloring. Other western hemisphere species of Oecanthus (not found in the United States) can be ruled out for non-matching characters as in Table 1.

Discussion
We describe a new species of Oecanthus that belongs to the nigricornis species group. This small Oecanthus species has a very pale greenish-white color that helps it blend in well with the similar pale whitish-green pastel color of the stem and leaf foliage of hoary rosemary mint, P. incana, shrubs growing on the white gypsum dunes. Although morphologically similar to O. quadripunctatus in some respects, several characters were dis-tinctly different: the subgenital plates of both males and females, the song pulse rate and frequency, and male tegmen width and length. A potential dwarf species of O. quadripunctatus, found in coastal central California on tarweed, was studied by Walker and Rentz (1967) and found to have the same song characters as fullsized O. quadripunctatus. Since the only difference found was its size, we ruled it out as being O. beameri sp. nov. The lack of dark lateral lines on the tibiae, and the commonly interrupted medial line on the scape rule out O. celerinictus.
We were able to separate O. beameri sp. nov. from other species in the nigricornis group by the following characters: the lack of black setae that are found on O. salvii; the antennal markings of O. argentinus and O. walkeri; and the lack of black, dark brown, rust, or mahogany color on the sternites of O. forbesi, O. laricis, O. nigricornis, and O. pini. O. beameri sp. nov. may be endemic to the gypsum dunes of White Sands, New Mexico (White Sands National Park, and likely also the gypsum dunes of White Sands Missile Range). O. beameri sp. nov. also appears to be specialized to live on hoary rosemary mint, based on occurrence and color matching. While O. beameri sp. nov. was common at White Sands on hoary rosemary mint, no individuals were heard singing from any of the other plants present. O. quadripunctatus is known to occur throughout New Mexico (SCAN 2021; search for O. quadripunctatus from the collections of the Museum of Southwestern Biology, University of New Mexico, and from the Insect Collection, New Mexico State University). Additionally, field collecting at White Sands revealed that O. quadripunctatus was not found there, and O. beameri sp. nov. was not found in locations adjacent to White Sands.