Morphological, molecular and ecological characterization of a native isolate of Steinernema feltiae (Rhabditida: Steinernematidae) from southern Chile

Abstract

Background: Steinernema feltiae is an entomopathogenic nematode used in biological control programs with a global distribution. Populations of this species show phenotypic plasticity derived from local adaptation and vary in different traits, such as location and host penetration. The aim of this work was to describe a Chilean isolate of this nematode species, using integrative approaches.

Methods: Nematode morphological and morphometric studies were conducted along with molecular analysis of nuclear genes. The symbiotic bacterium was also identified by sequencing the 16S rRNA gene. Some ecological characteristics were described, including the temperature requirements for the nematode life cycle and the effect of soil water content for optimal reproduction.

Results: Morphometric characterization revealed a large intra-specific variability. The isolate identity was also corroborated with the analysis of nuclear genes. Based on the 16S gene, its symbiont bacteria, Xenorhabdus bovienii, was identified. The lowest, optimal and highest temperatures found to limit the infestation and reproduction on Galleria mellonella were 10, 20 and 30 °C, respectively; the emergence from the host larvae occurred approximately 10 days after inoculation. Differences were observed in offspring, and 120 infective juveniles (IJ)/larva was the most prolific dose at 20 °C. The soil water content did not affect the number of IJ invaders, penetration efficacy and IJ emergence time or offspring per larva, but it caused a delay in achieving full mortality at the permanent wilting point with respect to saturation and field capacity.

Conclusions: For the first time, a Chilean isolate of S. feltiae is described in detail considering morphological, molecular and ecological aspects. The isolate was shown to be efficient in soil containing water, with optimal temperatures ranging from 15 to 25 °C for host infestation and production of an abundant offspring; these characteristics would allow its potential use as control agents in a wide geographical area of the country.

Keywords: Adults; Biocontrol; Juveniles; Soil water content; Symbiotic bacteria; Taxonomy; Temperature; Xenorhabdus.

Fig. 1

Steinernema feltiae isolate from Lican Ray, Chile. Male, first generation. a Entire body; b, d cephalic region, showing lips, labial papillae and cephalic papillae and amphids; c anterior region, showing excretory pore location; e tail with mucron; f posterior region, showing genital papillae; f spicules and gubernaculum

Fig. 2

Steinernema feltiae isolate from Lican Ray, Chile. Female. First generation. a Entire body; b anterior region, showing esophagus and excretory pore. Second generation. c Entire body. First generation. d Vulvar region; e tail. Second generation. f Tail

Fig. 3

Steinernema feltiae isolate from Lican Ray, Chile. Third juvenile stage. a Anterior region, showing esophagus; b anterior region, showing cephalic papilla and amphid; c lateral field at midbody; d hyaline portion; e Tail

Fig. 4

Phylogenetic relationships of the ITS rRNA sequences of Steinernema spp. The 50% majority rule consensus tree from Bayesian analysis generated with the GTR+G model. Posterior probabilities are given in the nodes. Newly obtained sequences are in bold letters

Fig. 5

Phylogenetic relationships of the 28S rRNA sequences of Steinernema spp. The 50% majority rule consensus tree from Bayesian analysis generated with the GTR+G model. Posterior probabilities are given in the nodes. Newly obtained sequences are in bold letters

Fig. 6

Phylogenetic relationships of the 16S rRNA sequences of Xenorhabdus spp. The 50% majority rule consensus tree from Bayesian analysis generated with the GTR+G+I model. Posterior probabilities are given in the nodes. Newly obtained sequences are in bold letters