Species status of two populations of Encarsia sophia (Girault & Dodd) (Hymenoptera: Aphelinidae) native to different geographic areas.

Encarsia sophia is a cosmopolitan parasitoid of whitefly pests and is regarded as a potential biocontrol agent of the Bemisia tabaci species-complex. However, the possibility exists that under this specific name a complex of cryptic species may be contained, whose correct identification is essential for their effective use in biological control programmes. In this paper two populations native to Pakistan and Spain, respectively, were characterized by means of morphometric analysis, crossing experiments and karyological analysis. The two populations, indistinguishable on the basis of single morphological characters, were distinguished through a canonical discriminant function analysis. Mating tests showed rare copulation attempts and no transfer of spermatozoa into the spermatheca in heterogamic crosses, thus suggesting that the Pakistani and Spanish populations are reproductively isolated. Although the two populations shared the same karyotype formula (2n=2m+2sm+6a), consistent differences were found in their chromosome sets. In the Spanish population the metacentric chromosome was almost one half of the whole genome set (rl=44.23), while in the Pakistani one, it was shorter (rl=29.55) and as long as the sub-metacentric chromosome. Moreover, silver staining provided evidence of a different localization of the active nucleolus organizer regions (NORs). Results obtained in this study suggest that the Pakistani and Spanish populations are distinct cryptic species.