Molecular characterization of closely related species in the parasitic genus Encarsia (Hymenoptera: Aphelinidae) based on the mitochondrial cytochrome oxidase subunit I gene

The genus Encarsia Förster includes parasitoid species that are effective natural enemies of whitefly and armoured scale insect agricultural pests. Within this genus, several species groups have been recognized on the basis of morphological similarity, although their monophyly appears uncertain. It is often difficult to separate morphologically similar species, and there is evidence that some species could in fact be complexes of cryptic species. Their correct identification is fundamental for biological control purposes. Recently, due to unreliability of morphological characters, molecular techniques have been investigated to identify markers that differentiate closely related species. In this study, DNA variation in an ~900 bp segment of the mitochondrial cytochrome oxidase subunit I (COI) gene was examined by both sequencing and PCR–RFLP. Two pairs of species that are difficult to distinguish morphologically were analysed: Encarsia formosa Gahan and Encarsia luteola Howard, belonging to the luteola group, and two populations of Encarsia sophia (Girault & Dodd) from Pakistan and Spain, belonging to the strenua group, recently characterized as cryptic species. High sequence divergence and species-specific restriction patterns clearly differentiate both species pairs. Parsimony analysis of the nucleotide sequences was also performed, including Encarsia hispida De Santis (luteola group) and Encarsia protransvena Viggiani (strenua group). Two monophyletic clades supporting the two groups of species considered were resolved. The results of this study support the use of the COI gene as a useful marker in separating species of Encarsia, for which morphological differences are subtle. Moreover, the COI gene appears potentially useful for understanding phylogenetic relationships in this genus.