A new species of Oecanthus is described from Mexico. Oecanthus rohiniae sp. nov. occurs in central Mexico in the understory of tropical deciduous forest and is currently known only from Mexico. This new species has the coloring, antennal markings, slightly widened tegmina, and calling song that are found in the rileyi species group. Although morphologically very similar to Oecanthus fultoni, the shapes of the distal hooks on the male copulatory blades differ between the two species. There are also differences in the song pulse patterns and chirp rate response to temperature. This new species has been given the common name Cri-Cri tree cricket. Video and song recordings are available online.

bioacoustic, biodiversity, Querétaro, tropical deciduous forest

According to the Orthoptera Species File (Cigliano et al. 2020), the subfamily Oecanthinae Blanchard, 1845, is represented by nine genera: Oecanthodes Toms & Otte, 1988; Oecanthus Serville, 1831; Viphyus Otte, 1988; Leptogryllus Perkins, 1899; Prognathogryllus Brunner von Wattenwyl, 1895; Thaumatogryllus Perkins, 1899; Neoxabea Kirby, 1906; Xabea Walker, 1869; and Paraphasius Chopard, 1927. Two of these genera occur in Mexico—Oecanthus and Neoxabea. Twenty 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 2020b). These groups can be distinguished by characteristics including song type (chirping vs trilling and continuous vs intermittent); song pulse or chirp rate at given temperatures; 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 (Walker 1962, 1963, Walker and Collins 2010). Four species in the rileyi species group are currently known to occur in North America, Central America and the Caribbean (Walker 1967, Collins et al. 2014): O. alexanderi Walker, 2010 (Walker and Collins 2010); O. allardi Walker & Gurney, 1960; O. fultoni Walker, 1962; and O. rileyi Baker, 1905.

In 1960, Walker and Gurney published the description of O. allardi and included details of ten specimens of snowy tree cricket from Tamaulipas and Michoacán, Mexico. In 1965, Richard D. Alexander traveled throughout Mexico and recorded Orthoptera and other singing animals. Notes from his recordings include six tapes that mention ‘fultoni’ with adjectives such as slow, fast, and grouped or not grouped (Suppl. material 1: historical recordings). No further investigations of chirping tree crickets are known to have occurred in Mexico until the description of O. mhatreae Collins & Coronado, 2019 (Collins et al. 2019).

In 2019, a photograph accompanied by a sound recording (iNaturalist 2020) posted on iNaturalist.org from the central Mexican state of Querétaro led to the investigation of a new species of Oecanthus tree cricket. The chirping song pattern, widened tegmina, and orange area on the head are characters found in the rileyi species group. Although other photos from Mexico of tree crickets resembling the rileyi species group have been posted on iNaturalist, none had previously been accompanied by recordings of their songs. After reviewing all material, it was discovered that the samples did not correspond to any of the described taxa. This paper describes a new species of Oecanthus collected in Querétaro.

Specimens.—Adults and nymphs of Oecanthus were collected from a private property and immediate surrounding areas of Fraccionamiento Vista Real, Corregidora, State of Querétaro, Mexico. This locality is near Parque Nacional El Cimatario, on the southern slope of Cerro de Cimatario. Specimens were initially located by the song of the males and collected manually. Females and nymphs were found in the same area. Tree crickets were brought indoors in plastic containers (15 × 15 × 20 cm) with holes on the side for ventilation. The males and females were kept alive and separated to be recorded and then preserved in 70% ethyl alcohol for morphological studies. Photographs and measurements of diagnostic characters were made with a Jiusion Digital Microscope Model USB, magnification 40× to 1000× (ovipositor, cerci, and metanotal gland), MOTIC-SWZ168739 stereo-microscope at 40× and equipped with a 10 mp digital camera (internal genitalia). Characters considered for description are as follows: body length, head colors, antennal colors and markings, pronotum in dorsal view, tegmina length and width, stridulatory file, metanotal gland, cerci, subgenital plate, and internal genitalia (copulatory blades). Additional characters for females included the ovipositor, subgenital plate and cerci. 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); tegmina length (from the thorax joining point to distal end of tegmina along midline); tegminal width (measured at the widest section of tegmina at rest); hind femur length; and cerci length. The females’ ovipositors were measured from the base (closest portion to the abdomen) to the distal tip. Copulatory blades (Fulton 1915) project from the male genitalia complex and are situated just above the subgenital plate. These genitalia structures have also been referred to as pseudepiphallus (Chopard 1961, 1969), lophi medians [middle lobes] (Desutter 1987), or main lobe of pseudepiphallus (Zefa et al. 2012). The genitalia of Mexican specimens were treated with an aqueous solution of 10% potassium hydroxide (Rocha-Sánchez et al. 2018, Barrientos-Lozano and Rocha-Sanchez 2013). No chemicals were used on the O. fultoni specimen from the USA. Genus determination was made with keys from Walker (1967) and SINA (2020a) and review of taxa of Oecanthus in the Orthoptera Species File (Cigliano et al. 2020).

Calling song recording and analyses.—The male acoustic signal was recorded in the field and indoors using a Samsung Galaxy Tab S4 tablet model SM-T830, the app Grabadora Amazing, and a MixMart 8 GB, PCM, 1536 kbps digital voice recorder. Audio devices were tested for calibration by recording a reference time audio file with reference tones and comparing the results to the original file. The recording devices were kept at a distance of approximately 10 cm from the individual. Analyses of song recordings were made with the Raven Pro 1.6 program (Cornell Lab 2020). Audio waveforms were created using the programs Raven Lite 2.0 or Raven Pro 1.6 (Cornell Lab 2020). Grouped pulse patterns were determined by counting individual pulses within each chirp. A chirp consists of varying numbers of pulses, and each pulse corresponds to a single closure of the tegmina (Walker and Collins 2010). Ten randomly chosen chirp periods were measured for each recording to determine the chirps per minute rate for that sample. Additional recordings (Suppl. material 2: source recordings) from the Macaulay Library of Cornell Lab (2020) were used for the preparation of two graphs to compare chirps per minute vs temperature and carrier frequency vs temperature, with additional species in the rileyi group. Regression lines for the sampled O. rohiniae sp. nov. population were calculated in Microsoft Excel for Mac, Version 16.16.22 (200509) (2016). The slopes of the regression lines for O. rohiniae sp. nov. and O. fultoni were compared using the t-test procedure for paired samples from Wonnacott and Wonnacott (1977).

Climate.—Temperatures were measured using an ELMECO DTM2 digital thermocouple thermometer with a range of -50°C to 1000°C, with an accuracy of 0.1°C. Ambient temperature and rainfall ranges [climatologia/temperaturas-y-lluvias/resumenes-mensuales-de-temperaturas-y-lluvias] for 2018 and 2019 were taken from the National Water Commission weather website (NWC 2020). The light intensity was determined using a HIOKI model 3422 digital luxmeter with a range of 0 to 2000 Lx (1Lx accuracy) and using data from the NWC website.

We described a new species of Oecanthus that falls into the rileyi species group. We were able to rule out other chirping species by the following characters: Size and position of the black mark on the pedicel rules out O. rileyi; short chirps (less than nine pulses per chirp) rule out O. alexanderi and O. allardi; and the grouping of pulses in each chirp rules out O. mhatreae.

Oecanthus fultoni is morphologically quite similar to O. rohiniae sp. nov., however the distal hooks on the male copulatory blades of O. rohiniae sp. nov. have a slightly blunted point, while the hooks of O. fultoni are more sharply pointed. Recorded chirps of O. fultoni do not include the 2-3-2 pulse pattern as in chirps of O. rohiniae sp. nov. T-test analysis of the regression lines for chirps/min rate as it varies with temperature for O. rohiniae sp. nov. and O. fultoni indicated a significant difference between the two species.

A list of recordings by Alexander, which includes notations of ‘fultoni’ tree crickets, can be viewed in Suppl. material 1: historical recordings. In 1966, Thomas J. Walker analyzed several of Alexander’s recordings. With his permission, we provide a table of these analyses in Suppl. material 5: analyses of historical recordings. These recordings shed light on the need for further investigation of chirping tree crickets in Mexico. Although the Cri-Cri tree cricket is currently only described from Querétaro, there have been other photos from Mexico of similar looking tree crickets submitted to iNaturalist.

We thank the California Academy of Sciences for maintaining the website iNaturalist.org, which allows scientists and the general public from around the world to post photographs and sound recordings of insects. We are grateful to Thomas J. Walker, Professor Emeritus, University of Florida, for the wealth of knowledge he generously shares. We thank Thomas Moore, Professor Emeritus, University of Michigan, Museum of Zoology, for his diligent search for Alexander’s tapes. We also thank Ludivina Barrientos-Lozano, Professor and Researcher of Tecnológio Nacional de México-Instituto Tecnológico de Ciudad Victoria, and Alejandro Zaldivar Riverón, Professor and Researcher, Instituto de Biología, Universidad Nacional Autónoma de México, who offered lab facilities and assistance. Finally, we appreciate valuable suggestions by Tony Robillard , Edison Zefa, Klaus-Gerhard Heller, and an anonymous reviewer for improving this paper. The Orthopterists’ Society provided funding for publishing this paper.