A numerical taxonomic analysis of interspecific morphological differences in two closely related species of Cicada (Homoptera, Cicadidae) in Portugal

—Cicada orni Linnaeus is among the most common and widespread cicadas in Portugal, and, unless a critical study of the male genitalia is made, it is easily confused with the much less widely distributed C. barbara lusitanica Boulard. These species are morphologically very similar and sometimes difficult to separate using existing keys. This study attempts to test the discriminating capabilities of numerical techniques commonly used for classifica tory purposes, as well as to discover the most effective characters to distinguish between the two species. For these purposes, cluster analysis and principal component analysis were applied to a sample of 64 male specimens character ized by 40 characters (33 derived from the external morphology and 7 from genitalia). In WPGMA cluster analysis, product-moment correlations gave a better separation between these species than did taxonoinic distance coefficients; moreover, the analysis derived from the genital characters alone gave better separation than the analyses based on the 33 external characters. Principal component analysis yielded a clear, interspecific separation along the first axis. The best characters to discriminate between males of the two species were the lengths of the pygofer (and its dorsal spine), the tenth abdominal segment, and the appendages of the latter (which are smaller in barbara lusitanica), as well as the width of the shaft of the aedeagus (thinner in orni)' Finally, the uniformity of the general clustering pattern resulting from the two multivariate techniques suggests the presence of two distinct species, as also clearly indicated by behavioral data. Cicada orni Linnaeus is among the most common and widespread cicadas in Portugal, and, unless a critical study of the male geni talia is made, it is easily confused with the much less widely distributed C. barbara lusi tanica Boulard (Quartau and Fonseca 1988). As live specimens, however, they are easily distinguished by the male calling songs, which are quite distinct. Oscillograms are found in Claridge et al. (1979) and Boulard (1982), respectively, for C. orni and C. bar bara lusitanica. The two species are externally very similar and sometimes even difficult to separate by existing keys (e.g., Gomez-Menor 1957). In fact, the main distinguishing character used for their separation has been the presence in barbara of only two spots on the cross-veins of the forewings instead of four; however, some specimens of barbara lusitanica have the full four spots as they occur in orni (Fig. 4). Boulard (1982), when describing the Por tuguese form of C. barbara, which he origi nally named lusitanica, provided a good diag nosis of the genital characters of this species. However, no detailed comparison of the two sp cies has been made, nor has any type of multiple-character analysis involving the simu taneous use of several measurements or counts been attempted. It was felt of interest, therefore, to see how far some common tech niques of numerical taxonomy would discrim inate between this pair of closely related spe cies. This study was undertaken with two main objectives in mind. The first was to apply current techniques of numerical taxonomy commonly used for classificatory purposes with the aim of testing their general discrimi nating power with respect to these two spe cies. The techniques chosen were a form of hierarchical cluster analysis and principal component analysis. It is known that apart from the explicit use of the former, principal component analysis can also serve as a cluster technique of great generality and can be used to distinguish pairs of putative morphs as in the classical study of Temple (1968). The sec ond objective was to discover new characters that might help to separate C. orni from C. barbara. ^epto. de Zoologia e Antropologia, Faculdade de Ciencias de Lisboa, 1200 Lisboa, Portugal.