Oecanthus mhatreae Collins & Coronado

Collins, Nancy, Gonzalez, Isabel Margarita Coronado & Govaerts, Bruno Victor Alfons, 2019, Oecanthus mhatreae sp. nov. (Gryllidae: Oecanthinae): A new species of tree cricket from Mexico, with an irregular song pattern and unique chirp-like trill configuration, Journal of Orthoptera Research 28 (2), pp. 137-143 : 137-141

Oecanthus mhatreae Collins & Coronado sp. nov.

Etymology. -

Specific epithet in honor of Natasha Mhatre, who has worked extensively with Oecanthinae and has published many articles focusing on acoustic communication. The pronunciation of mhatreae is MAT-ray-ee [MAT] [ra-] [-ee]. The common name, Otomi tree cricket, is after the Otomí, an indigenous people of Mexico inhabiting the central Mexican Plateau region.

Type verification. -

The genus Oecanthus was determined by the presence of spines on the hind tibiae.

Type material. -

MEXICO, holotype ♂, alcohol vial, Querétaro, Corregidora, Fraccionamiento Vista Real, 20°52'20"N, 100°38'80"W; elevation ca 2130 m, understory of tropical deciduous forest, I. Coronado leg., 24 Jan 2019, deposited at Universidad Nacional Autónoma de Mexico (UNAM), Mexico City.

Paratypes: 1 ♀ and 1 ♂, 23-24 January 2019, and 1 ♀ and 1 ♂ 13 February 2019, same location as holotype, deposited at UNAM.

Male holotype description and measurements. -

(in mm). Light olive green wings with dark staining along some veins. Pronotum milky buff color. Grayish tan head with four lighter streaks running to pronotum, and light pink patch near scapes. Pedicel and scape pale green. Antennae pale greenish white. Eye color purplish. Palpi translucent tan. Oval black mark on each pedicel and scape. Abdomen light olive green with scattered darker blotches. Femurs translucent olive green; tibiae and tarsi light olive green. Body length 13.5; tegminal length 13.7; tegminal width 6.8; pronotal length 2.2; distal pronotal width 2.4; hind femur length 10; cerci 4.9. The stridulatory file length is 1.5 mm, and the stridulatory teeth count is 36.

Characters. -

Overall color of both sexes can range from light brown ( Fig. 1 ) to light olive green ( Fig. 2 ). Tegmina with dark staining along veins. Head grayish or brownish with small patch ranging from pink to peach. All individuals have four lighter colored vertical streaks on the distal portion of the top of the head extending to under the pronotal shield ( Fig. 3 ). The light brown individuals are not believed to be a true brown form of this species as the pronotum is equally buff colored to the pronotum on the olive green individuals. The patch of color on the head is located even with and just behind the scape. Pedicel and scape colors vary from whitish to greenish to brownish. Ventral surface of pedicel and scape each with one oval black mark ( Figs 4 , 5 ). The black mark is situated on a whitish field; however, dead specimens darken and the white may not be readily visible.

Antennae filaments translucent greyish white or tan. Eye color purple to brown. Palpi translucent tan. Pronotum has a milky or creamy buff or light olive color ( Figs 1-3 , 6 ). Tympanal membrane on fore tibiae whitish. Ventral abdomen with scattered, slightly darker blotches and speckles; color varies from light olive, buff or tan ( Fig. 7 ). Tarsi light olive or light brown, tibiae olive or tan, femora translucent light olive green or tan. Some individuals with whitish area at ventral femoral-tibial joints. Cerci straight and pale, extending beyond the distal edge of the tegmina. Hind wings do not extend beyond distal edge of tegmina. The metanotal gland photo ( Fig. 8 ) was taken of a dead specimen, and this species darkens from freezing euthanasia. Right tegmen stridulatory file as in Fig. 9 with 32-36 teeth; file length 1.4-1.7 mm.

Paratype males measurements: Body length 12.4-13.0; wing length 11.0-12.0; wing width 5.8-6.9; pronotal length 1.5-2.8; distal pronotal width 2.0; hind femur length 7.0-8.2; cerci length 4.3-5.0.

Paratype female measurements: Female with matching antennal markings and coloring as males. Body length 12.5-12.8; wing length 11.5-12.0; wing width 3.0-3.1; pronotal length 1.9-2.5; distal pronotal width 1.8-2.0; hind femur length 7.5-8.8; cerci length 6.5-6.6; ovipositor length 6.25-6.5. Ovipositor extends slightly beyond the tips of the cerci ( Fig. 10 ).

Nymphs as in photos of 3 rd– 5th instars ( Figs 11-13 ).

Habitat. -

Tree crickets were found on ten plant species: Anisacanthus pumilis (F. Dietr.) Nees; Cnidoscolus multilobus (Pax) I. M. Johnston; Colubrina triflora Brogn. Ex Sweet; Croton ciliatoglandulifer Ortega; Dasilyrion parryanum Trel; Iresine cassiniliformis S. Schauer; Justicia candicans Nees L D Benson; Ruta graveolens L; Senecio salignus DC.; and Thunbergia alata Bojer ex Sims ( Martínez and Sandoval 2017). Of these plants, R. graveolens , C. multilobus , and T. alata are introduced species. The only plants Otomi tree crickets were witnessed as actively feeding upon were C. ciliatoglandulifer , a native plant, and on C. multilobus and T. alata , which, unlike the native vegetation, are evergreen plants ( Calderón de Rzedowski and Rzedowski 2001).

Climate. -

According to records on the National Water Commission website, rainfall totals for Querétaro were (listed in mm from January 2018 through March 2019): 9.2, 10.0, 2.8, 24.1, 39.5, 161.8, 31.4, 71.7, 110.2, 58.6, 31.1, 3.8, 7.5, 2.3, and 4.6. The lowest temperatures occurred in January 2018 (5.3°C in 2018 and 8.5°C in 2019). The warmest temperatures from January-March 2019 were 24.7°C, 28.1°C, and 29.6°C.

Behavior. -

Light intensity readings ranged from less than 5 W/m2 to 12 W/m2 at the time males began singing. Song monitoring in January and February revealed Otomi tree crickets began singing from one minute before to eleven minutes after sunset and were singing within 10 minutes of sunset in temperatures of 17-18°C and past midnight in temperatures less than 12°C. The holotype male and one paratype female were video recorded mating while in captivity. A video clip can be viewed at www.oecanthinae.com.

Calling song. -

The song pattern and chirp configuration of Otomi tree cricket were instrumental in diagnosing this new Mexican oecanthine. Waveform analysis showed that each chirp was comprised of a long string of pulses with no groupings ( Figs 14-16 ). The recordings taken in the field and in captivity by IMCG were at temperatures of 14° C– 19°C. The carrier frequency of the calling song at 17°C was slightly above 2.6 kHz ( Fig. 17 ). One recording revealed the intermittent long chirp song of interest with a faster chirping species in the background ( Fig. 18 ). The faster chirping was 3-4 times faster than the long chirping of this new species, affirming the slow rate of the target species while the highly regu lar spacing of the background singer affirmed the irregular pattern of Otomi tree cricket. The irregular chirping pattern and the ungrouped chirp configuration of this new species were compared to the patterns and configurations of four other chirping species, two intermittent trilling species, and one continuous trilling species ( Fig. 19 ). The four chirping species in the rileyi species group display grouping of their pulses.

Oecanthus varicornis , from the varicornis species group, has continuous trilling with runs of pulses over several seconds, while O. mhatreae sp. nov. chirps never exceed 0.7 second. Of the three intermittent bursts of trilling species, O. niveus has a J-shaped mark on the scape ( Walker 1962). The second species, O. exclamationis , has markings on the pedicel and scape that resemble an inverted exclamation mark ( Fulton 1915). The third intermittent bursts of trilling species, O. leptogrammus , does have an irregular pattern similar to O. mhatreae sp. nov.; however, the coloring and antennal markings are markedly different for these two species. Oecanthus leptogrammus is very pale green ( Collins et al. 2014) and has a thin black line on each pedicel and scape ( Walker 1962).

At all temperatures, the chirping pattern of Otomi tree cricket was irregular. This sporadic rate and pattern were unlike any of the other known chirping species in North America. Fig. 20 shows the irregular rate at a variety of temperatures and includes a sample of the early evening warm up song heard most evenings. Since Otomi tree cricket has an irregular chirping pattern, a trend line graph cannot reliably be used for comparison with chirpers with regular patterns. The chirp rate at recorded temperatures was plotted for comparison to the other known songs ( Walker 2019b, Cornell Lab 2019) of North American chirping species ( Fig. 21 , Table 1). The graph displays the general niche that each of these five species occupy.

Diagnosis. -

Characters that separate O. mhatreae sp. nov. from other chirping species of tree crickets in the rileyi species group include: 1) аn overall darker coloring than the usual very pale green; 2) dark speckles and blotches on the abdomen; 3) dark staining along veins of the tegmina; 4) milky buff or olive color of the pro notum; 5) no grouping of the pulses in individual chirps; and 6) an irregular chirping pattern.

Fourteen species of Oecanthus found in the Western Hemisphere are not associated with an established species group and not all have recordings of songs available online. Otomi tree cricket’s stridulatory teeth count, antennal markings, and song type were compared to those fourteen species, but no matches were found (Table 2).

Figures

Fig. 10. Adult female coloring and ovipositor length (on non-native Ruta graveolens L.).

Fig. 17. Audio recording of the calling song of O. mhatreae sp. nov. at 17 ° C showing a carrier frequency of slightly above 2.6 kHz.

Fig. 18. Calling song recording of O. mhatreae sp. nov. at 17 ° C. The clip was amplified to highlight the background song. This 30 - sec clip shows the irregularly spaced O. mhatreae sp. nov. chirps at a rate of 28 pulses per minute with a yet to be determined chirping species in the background with a highly regular pattern at a rate of 100 chirps per minute.

Fig. 19. Comparisons of song patterns, single chirps and single bursts of trilling. O. mhatreae sp. nov. recorded in Queretaro. All remaining recordings in library of NC. Oecanthus leptogrammus and O. allardi recorded in Nicaragua; remaining species recorded in the United States.

Fig. 20. Oecanthus mhatreae sp. nov. males chirping in various temperatures.

Fig. 21. Graph comparing chirps per minute at given temperatures.

Figs 1 - 5. Oecanthus mhatreae sp. nov.: 1. Light brown male. 2. Light olive tone male. 3. Adult female head and pronotum. 4. Antennal markings on holotype male. 5. Antennal markings on paratype female.

Figs 6 - 9. Oecanthus mhatreae sp. nov.: 6. Singing male showing buffy pronotum (on native plant Dasilyrion parryanum Trel.). 7. Adult female showing blotching on ventral abdomen. 8. Metanotal gland. 9. Stridulatory file and teeth.

Figs 11 - 13. Oecanthus mhatreae sp. nov.: 11. Abdomen pattern of 3 rd instar nymph. 12. Female 4 th or 5 th instar nymph. 13. Male 4 th or 5 th instar nymph.

Figs 14 - 16. Waveforms of the calling song of O. mhatreae sp. nov. at 17 ° C: 14. Chirping for 15 seconds. 15. Three chirps. 16. A single chirp (0.5 sec duration) with 26 ungrouped pulses.