A Numerical Taxonomic Analysis of the Peripsocidae of the Oriental Region and the Pacific Basin

Abstract

The relationships of 83 species of psocids of the family Peripsocidae (Insecta: Psocoptera) were analysed numerico-taxonomically, using alternative methods of processing. The results of using different sets of adult morphological characters and different combinations of them were compared. The effect of admitting a large number of species with incomplete data (known from one sex only) into the system was investigated. Certain modifications of the accepted classification of the family were suggested. Numerical taxonomy was developed to provide an objective and repeatable method of evaluating the phenetic affinity between taxonomic units (see Sokal and Sneath, 1963). The method rests on the hypothesis that there are no special groups of genes the effects of which are confined to single mQrphological regions, and that a random sample of the genotype is best obtained by sampling many and various characters. A large number of characters is used and each character is considered to be of equal weight, and the larger the number of characters used, the more stable is the value of the overall similarity coefficient, up to an asymptote which will vary for each analysis. Rohlf (1963) used numerical taxonomic methods to compare the classification of Aedes using only adult characters with that using only larval characters and found a definite though low correlation between the resulting classifications. In 1963 Sokal and Michener (see Rohlf, 1963) compared the results of classifications based on female and male, and on head and non-head characters, and found similar values of correlation. In the study reported here species with incomplete data (known from one sex only) are admitted to the analysis by degrees, and the effect of these admissions on the classification based on individuals with information on both sexes is noted. Also, different sets of characters are omitted in different analyses and the results compared. Alternate methods in the processing of data are used, in order to find the combination best suited for the classification of Peripsocidae. MATERIAL AND METHODS General.-Eighty-three species of the family Peripsocidae representing three of the five genera were examined, using numerical taxonomic methods. Previously described species of which examples were unobtainable were not included in the study, due to reason which will be obvious later. A preliminary survey was run to find some 60 characters that vary among species (Sokal and Sneath, 1963). These characters were then carefully studied and their characteristic expression or dimensions recorded, males and females separately. Whenever possible, five of each sex (selected at random) were used. This figure represented over 30% of the sample in hand in 75% of the species studied. In the present study 146 characters were used, comprising 52 asexual characters, 52 female charters and 42 male characters. The distribution of these characters over the animal was as follows: 14 head characters, 45 thoracic characters and 87 abdominal characters. Of these, 90 are descriptive, 16 metric, 20 ratios, and 20 meristic. A histogram of these characters and the number thereof applicable to Ectopsocus and Peripsocus is provided in Fig. 1; the species, their code numbers, and the number of individuals used in this study are listed in Table 1. A description of characters in some detail can be found in the manuscript of a thesis by the junior author submitted for the degree of Ph.D. at the University of Hong Kong. Analyses of the distribution of the number of states for the various types of