Tibicen pronotalis walkeri

Hill, Kathy B. R. & Marshall, David C., 2009, Confirmation of the cicada Tibicen pronotalis walkeri stat. nov. (= T. w alk er i, Hemiptera: Cicadidae) in Florida: finding singing insects through their songs, Zootaxa 2125, pp. 63-66 : 63-64

Tibicen pronotalis walkeri in the eastern USA

Sanborn et al. (2008) list the publications that state that T. p. walkeri occurs in Florida (e.g., Uhler 1884, Davis 1925, 1935, 1938), and discuss reasons to doubt these records, which give only vague locations such as “Florida” or “western Florida”, and do not refer to actual specimens. However, Sanborn et al. did not discuss Davis’ (1915) record of a specimen labelled “Florida” and recorded as deposited in the Museum of Comparative Zoology (MCZ, Harvard University, Boston, USA). Sanborn et al. (2008) searched through many museum collections, including the W. T. Davis collection and the MCZ but came across no specimens of T. p. walkeri from within the Florida (or Georgia) borders, and so concluded that published records were probably misidentifications of other eastern USA Tibicen , many of which are difficult to distinguish morphologically and have a confused nomenclatural history. Our new records suggest that W. T. Davis had seen at least one specimen of T. p. walkeri from Florida (e.g., Davis 1915), although that specimen is now apparently lost.

Tibicen pronotalis walkeri is one of the largest cicadas in the eastern USA [13 specimens from throughout the USA measured: body length 35–40mm, tegmina (forewing) length 47–53mm, wingspread 107–124mm], with a robust body, relatively narrow head compared to the pronotum width, and green or orange and black colouration (e.g., Fig. 1a). It would be interesting to compare series from across the range of T. pronotalis Davis , as there appears to be a cline in morphology from generally larger, very green specimens in the east to generally smaller, darker and usually orangecoloured specimens further west—this would also help in determining if the two subspecies are valid. Specimens of T. p. walkeri from Florida ( US.FL.RIV site, see below) and from Texas ( US.TX.EDN site, Texas: Jackson Co., just N. of Edna) differ at 1.2% of 1456bp of mitochondrial cytochrome oxidase I sequence (unpublished data).

East of approximately the 95th meridian, the song of T. p. walkeri (Fig. 1c) is diagnostic and not likely to be confused with any other species. The song consists of a coarse buzz that rises and falls rhythmically in frequency and amplitude at approximately 2-3 “revs” per second [zhii–zhii–zhii etc. (Z’we Z’we, Beamer 1928)]. This continuous revving sound is occasionally punctuated by several seconds of quieter, smoother, “idling” sound. Analysis of three recordings from the new eastern records found a main oscillation (“revving”) rate of 2.3 cycles/s (±0.4 standard deviation; slower at colder temperatures). The pattern alternates between sections containing a uniform timbal-click rate and sections with 7-9 groups of timbal-clicks, the uniform-rate sections being 2.0 ±0.1 times longer than the latter. The timbal-click rate in the uniform sections was 441.1 ±24.1/s, while the groups of timbal-clicks were produced at a rate of 55.6 ±6.8/s. The overall dominant frequency was 4.1 ±0.4kHz. (Songs were recorded using a Marantz PMD-670 Digital recorder sampling at 48kHz with a Sennheiser omnidirectional ME62 microphone mounted in a Sony PBR-330 parabola. Songs were analysed using Raven Pro v. 1.3, Cornell Lab of Ornithology, New York. Air temperature during recording was approximately 24-28°C, estimated from www.wunderground.com.)

T. p. walkeri calls sporadically during much of the day (e.g., see records below, also Beamer 1928), however it is especially active at dusk, and all males in an area may be silent for long periods of time in the morning and afternoon. In the south-central USA, from approximately the 95th Meridian west, T. pronotalis is replaced by its close relative T. dealbatus Davis which appears to have the same song and habitat but distinctive morphology (e.g., Beamer 1928, Davis 1935). This situation, morphological distinctiveness with indistinguishable songs, is rare in cicadas and in singing insects generally.

Our records of T. p. walkeri in the eastern USA (below) are all from late July and early September, however records from central states suggest that adults could be active in Florida and Georgia as early as June and as late as October ( Beamer 1928, Davis 1938, Froeschner 1952, pers. obs.). T. p. walkeri is strongly associated with willows ( Salix spp.) and cottonwoods ( Populus spp.), usually growing along rivers (e.g., Beamer 1928, Davis 1935). Listening for songs along more of the rivers in northern Florida and in Georgia (e.g., see Fig. 1b), especially where willows and cottonwoods are growing, is likely to produce more records of T. p. walkeri in the eastern USA—we have found this species as far east and north as Montezuma, Georgia (see below).