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Oecanthus walkeri: a new species of tree cricket from Texas.

Introduction

As listed in the Orthoptera Species File (OSF) online (Eades et al. 2012), the genus Oecanthus is comprised of 62 species. OSF is an Orthoptera database which provides multiple references for each species, including descriptive articles when available. Walker & Collins (2010) divide North American Oecanthus into four main groups: nigricornis, niveus, rileyi and varicornis. These groups can be distinguished by characteristics including: coloration of the head, pronotum and abdomen; antennae color; antennal markings on the pedicel and scape; tegminal morphology; song character (chirping vs trilling and continuous vs intermittent); and song pulse rate at given temperatures. Seven species from the O. nigricornis group of Oecanthus occur in the USA: O. argentinus, O. celerinctus, O. forbesi, O. laricis, O. nigricornis, O. pini and O. quadripunctatus.

A 2009 field trip to the Rio Grande Valley in southern Texas led to the discovery of a new nigricornis, group species. Individuals were located by following the singing of males in Seep Willow (Baccharis salicipholia), Tepejuage (Leucaena iveruienta) and Sugar Hackberry (Celtis laevigata) trees. The constant trilling song of this species can be heard both day and night, while a song pattern of intermittent bursts is heard only at dusk.

Song analysis, morphology and distribution were all instrumental in diagnosing this new Texas Oecanthine. Information on habitat and behavior is provided. DNA sequencing results and phylogenetic comparisons will be offered in a future paper by LS. Photographs and video of O. walkeri are in Supporting Material.

Materials and methods

Photographs ofthe holotype and videos of paratypes will be made available for viewing at OSF, Macaulay Library, www. oecanthinae. com and Singing Insects of North America: crickets and katydids (SINA).

Type verification.--According to current listing on OSF, there are eight genera of Oecanthinae worldwide, but only two occur in the USA and Mexico--Oecanthus and Neoxabea. Genus level for these specimens was identified using the key from Walker (1967). The genus of Oecanthus was determined by the presence of spines on the hind tibiae, and lack of a tubercle on the distal border of the scape.

Species group was determined using the Key to Species Groups of Oecanthus found on the SINA website (Walker 2012). Members of the O. nigricornis group of Oecanthus have a continuous trilling song and 3 or 4 black marks on the scape and pedicel. The O. varicornis group also has a continuous trilling song, but wider tegmina than the O. nigricornis group, and only 2 marks on the scape and pedicel. The O. niveus group produces intermittent bursts of trilling, and has 2 black marks on the scape and pedicel. The O. rileyi group makes regularly spaced chirps and has 2 black marks on slightly raised ivory/white fields on the scape and pedicel.

Several characteristics are informative for identifying species of Oecanthus: 1) presence vs absence of markings on the front of the first and second antennal segments (the scape and the pedicel), which are generally similar in each group and often unique to each species. When present, these markings should be examined for number, size, shape, position and configuration. It should be noted that nigricornis species-group markings are sometimes similar enough to make species identification difficult. 2) Head color, or the shape, area and intensity of patches of color on the head. 3) The color(s) of the ventral abdomen: appearance is solid or patterned. 4) Tegminal size, shape and occasionally notable vein pattern differences. 5) Number of teeth on the file--usually located on the male's right tegmen. 6) Number of pulses per second in the song of a male at a given temperature. There is a linear relationship between ambient temperature and male pulse rate across the biologically relevant temperature range.

Morphology

Collection methods.--Areas inhabited by oecanthines were determined by locating actively singing males. Inhabited trees were then searched for adults of both sexes and for instars. Most specimens were collected by shaking or by bending downward pliable branches; only the holotype and a female paratype were found at eye level.

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Habitats.--O. walkeri was found in Seep Willows (Baccharis salicifolia) at Resaca de La Palma State Park (RDLPSP), Cameron County, Texas. At Bentsen-Rio Grande State Park (BRGVSP), Hidalgo County, Texas, O. walkeri was found in Sugar Hackberry trees (Celtis laevigata), Tepejuage trees (Leucaena iveruienta) and multiple groups of Seep Willows. Collection dates were May 2009 and June 2010 by NC and LS.

Preservation of specimens.--Males and females were collected and photographed; singing males were video recorded. Measurements and visual observations for morphological study were made after the specimens were euthanized using acetone. Specimens were preserved in alcohol or with anhydrous calcium sulfate drying crystals. Wings were removed from some specimens in order to photograph the teeth on the stridulatory file.

Depositories.--

FSCA-Florida State Collection of Arthropods--Gainesville, USA

UWM-University of Wisconsin-Madison, USA

DC-Dartmouth College, Hanover, New Hampshire, USA

Morphological measurements.--Dimensions in mm of holotype male. Total body length refers to the midline length from the fastigium to the apex of the subgenital plate--not including antennae, tegmina, limbs or cerci. Tegminal width is measured at the tegmina widest section, while resting atop the abdomen of the male. Pronotal length was measured along the medial line of the pronotum.

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Antennal markings.--The antennal markings found on the ventral surface of the pedicel and scape were photographed using a Canon PowerShot S5 IS digital camera.

Song and temperature recordings.--The digital camera was also used to record songs; it was set in video mode at 30 frames/sec, with the camera held as close to the singing tree cricket as possible. The sound track had a sample rate of 44100 Hz, with a 16-bit sample size. An avi-to-wav converter marketed online by 008soft.com was used to extract the sound track from the video file. AVS4YOU Audio Editor Software version 4.2 was used to analyze the sound tracks and to make images of their waveforms. Temperature was measured within 15 cm of actively singing males using a hand-held digital thermometer manufactured by LaCrosse Technology, model WS-9029U. Accuracy of the digital thermometer was confirmed by its immersion in a water bath, comparing its readings with those of a precision glass laboratory thermometer.

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Results

Oecanthus walkeri Collins & Symes, n. sp.

Etymology.--Oecanthus walkeri Collins & Symes n. sp. Named in honor of Thomas J. Walker, Professor Emeritus, University of Florida, Gainesville. Dr. Walker has studied orthopterans his entire career, has published a wealth of articles, and described many species, including 16 oecanthines. His first Oecanthinae description was with A. B. Gurney, of Oecanthus allardi in 1960; his most recent was Oecanthus alexanderi in 2010 with N.J. Collins.

Holotype.--Male (Fig. 2). Located on Seep Willow (Baccharis salicifolia), at Bentsen-Rio Grande Valley State Park, 7 Jun 2010, GPS-N 26[degrees] 11.127, W 98[degrees] 22.838; altitude 33.9m, N.J. Collins, collector; FSCA. Body length (mm) 16.0; tegminal length 12.0, tegminal width 4.3; pronotal length 2.9, rear pronotal width 2.8; hind femur length 9.0. Right tegminal stridulatory tooth total 47. Antennal markings on first two antennal segments as in Fig. 1. Song as in Fig. 6-8. Video and photograph of living holotype in Supporting Material.

Paratypes.--

(1) Female: located on same branch as holotype. Deposited at FSCA. (1) Male: located at BRGVSP. Deposited at UWM. (1) Female: located at BRGVSP. Deposited at UWM. (1) Male: located at RDLPSP. Deposited at DC.

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Description.--Overall color of both sexes light green, often with small amount of yellow on head/face. Eye color yellow. Palpi pale brown or gray. Prominent areas of bright white color on borders of pronotal area. Ventral abdomen pale creamy white. Pedicel and scape pale anteriorly, pure white posteriorly. Antennal markings (Fig. 1): pedicel with two vertical black marks, scape with two black marks--inner is vertical and outer horizontal. Antennae dark, often deep black. Tympana on foretibiae light gray. Tarsi black, tibiae dark gray distally graduating to green proximally, femora translucent green. Yellow-brown at femoral-tibial joints. Cerci pale and long (extending to tip of ovipositor in female). Male (Figs 2, 3): hind wings extend beyond distal edge of tegmina. Inner area of metanotal gland appears dark tan; outer rim appears pale green. Female (Fig. 4): prominent white bordering dorsal sides of abdomen. Latticed vein pattern on translucent wings. Instar (Fig. 5): dorsal abdomen medium green with bright white at both outer edges. A thin white line bordered with dark green runs from head to distal tip of abdomen.

Song Analysis.--The pulse rates of the continuous trilling of O. walkeri at given temperatures (Fig. 8) fall midway between those of O. argentinus and O. quadripunctatus (Fig. 9), and therefore reinforce its placement as a member of the O. nigricornis group. The dominant frequency of the song of O. walkeri is 4.1kHz (Fig. 6, 7D) at 19.1[degrees] C. Videos can be viewed in Supporting Material.

Discussion

Morphologically, oecanthines in the O. nigricornis species group are often difficult to distinguish based on antennal markings, since the intraspecific variation in markings often overlaps the interspecific differences. However two characters that do separate O. walkeri from other tree crickets in the nigricornis group are: 1) a white pedicel and scape with black flagellae, and 2) black flagellae in conjunction with a creamy white ventral abdomen.

Although O. walkeri could be confused with species in the niveus species group due to an interrupted trilling pattern earlier in the evening, its predominant call of continuous trilling matches those of other species in the O. nigricornis group. O. walkeri can generally be distinguished by song from O. celerinictus due to differences in pulse rate, especially under higher temperature conditions. The pulse rate of O. celerinictus falls at the higher edge of the range of the O. nigricornis group, while that of O. walkeri falls toward the lower edge of this range. While its pulses per second rate is similar to two Texas co-occurring species in the O. nigricornis group, O. quadripunctatus and O. argentinus, a distinguishing character of O. walkeri is their habit of dwelling in trees, whereas the aforementioned two species occur on ground vegetation and shrubs.

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This species is currently known only in extreme southern Texas and more investigation is needed to establish their geographic range, including Mexico. Given proximity to Mexico, the potential exists to find other new species along the Mexican-American border.

Acknowledgements

We thank David Riskind, Texas Director of Natural Resources for permitting studies in state parks, and George Cortez, Park Superintendent at Bentsen-Rio Grande Valley State Park for granting permission to collect specimens of this new species. We are grateful to Katherine Miller, Resaca de La Palma State Park Natural Resource Specialist, and to Joshua Stuart Rose and Javier de Leon, Bentsen-Rio Grande Valley State Park Natural Resource Specialists, for their guidance and assistance.

We are eternally grateful to Dr. Thomas J. Walker for the wealth of knowledge he generously shares and for his kind guidance in expanding our knowledge of Oecanthinae, as well as furthering our pursuit of increasing public awareness of tree crickets.

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References

Eades D.C., Otte D., Cigliano M.M., Braun H. 2012. Orthoptera Species File Online. Version 2.0/4.0. http://Orthoptera.SpeciesFile.org

Fulton B.B. 1915. The tree crickets of New York: life history and bionomics. N. Y. Agricultural Experimental Station. Technical Bulletin 42: 3-47. (http://entomology.ifas.ufl.edu/walker/buzz/s576lf15.pdf)

Walker T.J. 1962a. The taxonomy and calling songs of United States tree crickets (Orthoptera: Gryllidae: Oecanthinae). I. The genus Neoxabea and the niveus and varicornis groups of the genus Oecanthus. Annals Entomological Society of America 55: 303-322. (http://entomology.ifas.ufl.edu/walker/buzz/s576lw62.pdf)

Walker T.J. 1963. The taxonomy and calling songs of United States tree crickets (Orthoptera: Gryllidae: Oecanthinae). II. The nigricornis group of the genus Oecanthus. Annals Entomological Society of America 56: 772-789. (http://entomology.ifas.ufl.edu/walker/buzz/s576lw63.pdf)

Walker T.J. 1967. Revision of the Oecanthinae (Orthoptera: Gryllidae) of America South of the United States. Annals Entomological Society of America 60: 784-796. (http://entomology.ifas.ufl.edu/walker/buzz/s576lw67.pdf)

Walker T.J., Collins N.J. 2010. New world thermometer crickets: the Oecanthus rileyi species group and a new species from North America. Journal of Orthoptera Research 19: 371-376. (http://entomology.ifas.ufl.edu/walker/buzz/s576lwc10.pdf)

Walker T.J. 2012. Key to Species Groups of Oecanthus. Singing insects of North America: crickets and katydids. (http://entnemdept.ifas.ufl.edu/walker/buzz/g576k.htm)

Nancy Collins and Laurel Symes

[NC] Email: oecanthinancy@gmail.com

[LS] Department of Biology, Dartmouth College, Email: laurel.symes@dartmouth.edu
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Author:Collins, Nancy; Symes, Laurel
Publication:Journal of Orthoptera Research
Article Type:Report
Date:Jan 1, 2012
Words:2128
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