Studies on Xiphinema americanum sensu lato with descriptions of fifteen new species (Nematoda, Longidoridae)

Lima (1965) was the first to hypothesize that Xiphinema americanum Cobb, 1913 was a complex of different species in which he listed X. americanum, X. brevicolle Lordello et Da Costa, 1961, X. opisthohysterum Siddiqi, 1961 and four undescribed species (Lima, 1968). One of them was later described as X. mediterraneum Martelli et Lamberti, 1967 (Lamberti and Martelli, 1971) and recently synonymized with X. pachtaicum (Tulaganov, 1938) Kirijanova, 1951 (Siddiqi and Lamberti, 1977). The morphometrical variability in X. americanum was also studied by Tarjan (1968) who, after having examined 75 world-wide collected populations, concluded that the species status of X. brevicolle, X. opisthohysterum and Lima's Mediterranean species, presently X. pachtaicum, was justified but that all the other variations he had observed should be considered as geographical variants, correlated with climatic influences, within the X. americanum complex (Tarjan, 1969). In 1974 Heyns stated that «demarcation of species within the group is problematical and unsatisfactory although several of the species proposed by Lima seem to be justified ». Because of the importance of X. americanum as a vector of some plant viruses (Taylor and Robertson, 1975) we thought it useful to carry out studies which would clarify the identity of several populations from different geographical locations and establish the relationships with this and the other related species. This would contribute not only to better understanding of virus-vector specificity (Taylor and Robertson, 1975) but could also explain the failure of Some populations of X. americanum to transmit viruses for which it is considered an efficient vector. Therefore a study was made of several hundred populations belonging to the X. americanum group, either collected personally by the senior author or received from different parts of the world over a period of 15 years. Specimens were mounted in either glycerine or lactophenol.