Cytotaxonomic studies of Encarsia Forster (Hymenoptera : Aphelinidae)

A cytotaxonomic study was carried out on 13 species of Encarsia Forster, kn own to parasitize aleyrodids and diaspidids. The chromosomes varied greatly both in number and morphology, with E. protransvena Viggiani having the lo west chromosome number (2n = 6) and E. asterobemisiae Viggiani & Mazzone th e highest (2n = 20). The most common chromosome number was 2n = 10. C-bandi ng, G-banding and silver staining for nucleolar organizer regions (NOR) pro vided the possibility of distinguishing between karyotypes with the same ch romosome number and morphology and to identify all the pairs of homologues in a diploid set for advanced cytogenetic studies. The karyotype of Coccoph agus lycimnia (Walker) was also examined. The chromosome data suggested tha t in Encarsia, karyotype differentiation has mainly occurred through a seri es of centric fusions, although other rearrangements may also have been sig nificant. The importance of karyological data in systematic studies and in the identification of biotypes and cryptic species of economic interest is outlined.