EVOLUTION OF THE CHORTHIPPUS-BIGUTTULUS GROUP (ORTHOPTERA, ACRIDIDAE)IN THE ALPS, BASED ON MORPHOLOGY AND STRIDULATION

Males of Chorthippus biguttulus (LINNE, 1758), C. brunneus (THUNBERG, 1815), C. mollis (CHARPENTIER, 1825), C. mollis ignifer (RAMME, 1923), C. eisentrauti (RAMME, 1931) and an aberrant form of C. brunneus (Tic ino-brunneus) are compared on the base of morphological and acoustical characters. Discriminating morphological characters are the width of the costal and subcostal fields, the index ''costal: subcostal field'' , the index ''combined width of costal and subcostal fields: tegmen le ngth'', the index ''tegmen length: length of apical area'', the index ''tegmen length: postfemur length'', and the number of stridulatory pe gs. But even in a two-character analysis there is a gradual dine of ch aracters from C. brunneus via Ticino-brunneus and C. eisentrauti to C. biguttulus. Moreover, the range of morphological characters of C. m. ignifer greatly overlaps with those of C. eisentrauti, Ticino-brunneus and C. m. mollis. With regard to spontaneous stridulation of the male s, C. eisentrauti differs from C. biguttulus in having shorter verses which are more numerous per song and in a more irregular number of syl lables per echeme, of which there are usually three in C. biguttulus. Ticino-brunneus differs from nominate C. brunneus in producing longer verses with a higher number of pulses. The range of the verse length o f Ticino-brunneus also overlaps with that of C. eisentrauti. Stridulat ion of C. m. mollis has a soft ending as in the last echemes the tick- sound is absent; in C. m. ignifer the song ends abruptly with a tick i n the last echeme, and some echemes with a different syllable pattern can be loosely added. C. m. ignifer is reestablished as a good subspec ies on the basis of song characters. C. eisentrauti is regarded to be a sister species of C, biguttulus conserving many of the primitive cha racters of the C. biguttulus group. A zone of transient characters bet ween C. eisentrauti and C. biguttulus exists between Bivio and Calanda (Grisons); and a transient zone between C. eisentrauti and C. brunneu s between Bregaglia and the Upper Engadine. Ticino-brunneus possibly e volved by hybridisation between C. eisentrauti and C. brunneus. A hypo thetical scheme of the evolution of the taxa of the C. bigrcttulus gro up occurring in the Alps is presented and discussed.