Pristionchus seladoniae n. sp. (Diplogastridae) isolated from a eusocial soil-dwelling bee, Halictus (Seladonia) aerarius, in Nagano, Japan

Summary A new species of Pristionchus was isolated from a soil-dwelling bee, Halictus (Seladonia) aerarius, collected from Sugadaira, Nagano, Japan. The nematode was successfully cultured on nematode growth medium agar previously inoculated with the Escherichia coli strain OP50; however, it did not propagate well. Typologically, the new species is similar to other Pristionchus belonging to the maupasi, pacificus and lheritieri groups in the stomatal structure of stenostomatous form. However, the species is characterised by the relatively short, conical tail of the female and the arrangement of male genital papillae in which the second- and third-paired papillae are almost at the same level and one of these two are directed laterally. Phylogenetically, the nematode belongs to the maupasi group, the ‘American clade’ within the genus, and is separable from the other species in the group. Biologically, the species has several interesting characters: it is seemingly native to Japan, regardless of its phylogenetic group; it is in tight and specific phoretic association with a eusocial bee; it lacks a eurystomatous form (or this form occurs rarely) under cultured conditions; and it shows characteristic clumping behaviour on culture media. The new species is taxonomically described herein as Pristionchus seladoniae n. sp.