Entomoparasitic nematodes of the genus Skarbilovinema: S. laumondi and S. lyoni (Nematoda: Tylenchida), parasites of the flies of the family Syrphidae (Diptera), with phylogeny of the suborder Hexatylina

摘要

Morphological description of two entomoparasitic nematodes, Skarbilovinema laumondi and S. lyoni, parasitising flies from the genus Helophilus and Eristalis of the family Syrphidae (Diptera) are given. The life cycle of these nematodes is also presented. Phylogenetic analysis using the D2-D3 expansion fragments of the 28S rRNA gene and partial 18S rRNA gene sequences showed that Skarbilovinema has a sister relationships with Fergusoria sp. Sequence analysis revealed an anomalous mode of evolution for the ribosomal RNA genes in Skarbilovinema, which have long insertions, strong A-T nucleotide content bias and a high mutation rate. Difference in the D2-D3 expansion segments of 28S rRNA gene sequences between S. laumondi and S. lyoni was 23%, which is higher than usual sequence variation for nematode species belonging to same genus. Several long insertions make 18S rRNA gene and the D2-D3 of 28S rRNA gene the longest ribosomal rRNA genes in nematodes.