A total of 15 dried specimens were used, of which 12 specimens were collected from the Yaeyama Islands (Ishigaki-jima and Iriomote-jima Islands) and 3 from Okinawa-honto Island (Fig. 1). Morphological observations were made using an Olympus SZ61 binocular microscope. Digital images of the specimens were taken with a Nikon D200 digital camera body and Nikon AF Micro Nikkor 60mm f/2.8D lens, and with a Keyence digital microscope system (VHX-1000 digital microscope, VHX-S50 observation system, VHX-1100 multi scan, and VH-Z20R zoom lens).

Figure 1.  

Locations of Okinawa-honto Island, Ishigaki-jima Island, and Iriomote-jima Island.

The terminology used herein generally follows that of Davis (1966). The apparent labial segments I, II, and III are here referred to as rostral segments I, II, and III; these apparent labial (rostral) segments I, II, and III correspond to the “true” labial segments II, III, and IV, respectively.

All materials including type specimens have been preserved in the Insect Collection (IC) at the Laboratory of Entomology, Tokyo University of Agriculture, Japan (ELTUA).

As described above, T. miyamotoi shows a remarkable intraspecific variation in coloration, although its external morphology is insignificantly variable among the specimens obtained throughout its distribution range. Interestingly, the variation is discontinuous and clearly geographically separated between the Yaeyama and Okinawa-honto Islands (Fig. 1). As the two populations occurring in these two island groups are different in coloration, with the sea lying between the two areas as a physical barrier, it is possible that each of the populations could be recognized as a subspecies; however, we postpone any final conclusion about the subspecies until more specimens of this species, especially those from Okinawa-honto Island, are studied further.

Major differences in coloration within the species have been recognized in other congeners of Tiarodes. Cai et al. (2001) documented various color patterns of abdominal venter in T. venenatus Cai and Sun in Cai et al., 2001 and T. pictus Cai and Tomokuni in Cai et al., 2001. The former was described from mainland China (Zhejiang, Fujian) and Taiwan based on five specimens, and the latter from Taiwan based on seven specimens (Cai et al. 2001). However, based on their descriptions and illustrations, the variability appears to be continuous in each species with no relation to geographical tendency or gap. Therefore, this is the only example of discontinuous variation documented in the genus Tiarodes so far.

In Tiarodes, approximately 90 species have been described (Miller 1959, Cai et al. 2001, Tomokuni and Cai 2002, Ishikawa et al. 2005, Ishikawa and Miyamoto 2012). Most species have been described based on a single or few specimens owing to their limited abundance, and were distinguished from each other mainly by differences in coloration. Miller (1959) provided comprehensive identification keys for more than 80 species, using primarily coloration characteristics. Since the presence of remarkable intraspecific variations in coloration is evident as mentioned above, it is possible that two or more populations actually belonging to one species have been described as different species in the congeners of Tiarodes. Therefore, it is necessary to accurately evaluate the color characteristics defining a species of Tiarodes to revise the taxonomy and descriptions. In addition, it is also important to detect informative characters from the external morphology and to analyze molecular data to effectively discriminate between Tiarodes species.