Steinernema spp. (Steinernematidae, Rhabditida) infective juveniles in the soil of a mixed forest in Vladimir region, Russia: year-round observations

Summary

The population structure of Steinernema infective juveniles (Steinernematidae, Rhabditida) was studied in an experimental plot (10 × 10 m) over the course of a year. Soil samples from two layers (0-5 and 5-10 cm from the surface) were collected in a mixed forest (126 samples). Nematodes were extracted from soil by two centrifugations (water and MgSO4 solution), and identified by the examination of morphology and selectively by ITS rDNA sequencing. Infective juveniles of entomopathogenic nematodes, along with plectids, were the dominant groups of soil nematodes. Two steinernematid species, Steinernema kraussei and S. poinari, were detected. Their abundance in the samples was negatively correlated. The steinernematids were distributed in an aggregated manner (the random factor ‘sample collection point’ explained 36% of the variation in abundance). In the majority of soil samples, their abundance averaged 0.02 ± 0.04 ind. g^–1 (mean ± standard deviation). However, in a few samples (10 out of 126), the abundance exceeded the background average by more than an order of magnitude (0.22-5.43 ind. g^–1). The effects of soil layer, sample weight, and sampling date (or soil temperature) on the abundance of steinernematids were not significant. Soil freezing from January to April did not affect nematode numbers. Active live juveniles were isolated from frozen soil even in February (soil temperature –1.5°C).