Taxonomy And Identification Of Two Insectivorous Nematode Populations S11and JL11of The Genus Pristionchus

Insectivorous nematodes are variety and widely distribute in soil and in insects. According to incomplete statistics, there are over31handreds species of insectivorous nematodes that can be parasitic in more than700species of insects. So insectivorous nematodes are studied and utilitied as important agents in biological control field.The two populations of insectivorous nematodes, S11and JL11, were isolated from two soil samples collected from tea garden of changshu Jiangsu province and orchard of liquan Shanxi province, respectively. The two populations are morphologically similar, different in size. The body of S11is slightly biger than JL11. Sll:Body length of female=1036(774-1343)μm, D=53(37-65) μm; Body length of male=1040(830-1389)μm, D=53(37-65) μm; Body length of hermaphrodite=1620(1422-1728) μm, D=53(37-65) μm. JL11:Body length of female=886(795-979) μm, D=44(34-55) μm; Body length of male=883(784-977) μm, D=43(36-53) μm; Body length of hermaphrodite=1127(1050-1260) μm, D=61(54-77) μm. The difference of ITS sequence between these two insectivorous nematode populations is three, and that of18S rDNA sequence between them is two. The difference of18S rDNA sequence between them with other described species of genus Pristionchus is from26to28bp. The difference of18S rDNA sequence between them with Pristionchus pacificus is the smallest (26bp). The hybridization rate between JL11and S11was4%, and hybrids breeding ratio was48%, which indicated that the two insectivorous nematode populations belong to the same species with subspecies diverse. Molecular phylogenetic trees based on18S rDNA sequences revealed that the two populations were belong to the genus Pristionchus. The two strains share common morphologic characters with all the other species of genus Pristionchus:head region round anteriorly, six deeply divided lip sectors each bearing a single outer labial papilla, and connected by an anteriorly flanened, thin surrounding cuticle; two faint oval-shaped amphid openings at the base of the non-indented lip region; esophagus present and long, median bulb and basal bulb present, cuticle annulated and longitudinal ridge; oval excretory pore near the basal bulb of the postcorpus, vulva transverse, occasionally protruding; spicules of male adult paired, separate, symmetrical, slightly curved ventrally, head of spicules with rounded anterior end, five papillae formulas on each side of spicules; male tail with a narrow bursa. The two populations have many special characteristics that can significantly distinguish them from other species in the genus Pristionchus:Infective juveniles have larger size (408-435μm); anal of hermaphrodite apparently protruding, and the surface with ridges16to18; the distribution of male genital papilla is different around tail. Phylogenetic analysis showed that these two nematodes have the closest relationship with the Pristionchus pacificus. Integrated morphological and molecular data, the two populations S11and JL11are determined as a new species of the genus Pristionchus (Diplogasteridae: Rhabditida).