Characterization of populations of entomopathogenic nematodes isolated at diverse sites across Israel

Abstract

Entomopathogenic nematodes (EPNs) are known as effective biological agents against soildwelling stages of insect pests. In the present study new EPN populations from the Steinernematidae and Heterorhabditidae families were isolated at different locations in Israel. The newly isolated populations were subjected to a series of bioassays for beneficial traits, for selection of a superior isolate for biological control of insect pests. Nematode motility was measured in sand columns, with and without the susceptible insect Galleria mellonella. Infectivity was evaluated using an invasion rate assay, as well as a dose response assay in which LD 50 values were calculated. Nematode tolerance to environmental stresses was examined in heat and desiccation tolerance assays. The reproductive potentials of the new isolates were assessed in cadavers of G. mellonella. All Steinernematid populations were identified as Steinernema feltiae and the Heterorhabditids as Heterorhabditis sp. Large variation between the various populations was recorded in all assays. In order to identify a superior isolate, each strain was scored as 1 if its performance did not differ significantly from the highest level recorded in the particular assay; −1 if its performance did not differ significantly from the lowest level; and 0 if its performance was between the highest and lowest levels or did not differ from either. The scores for the different traits were then summed for each population and the totals were compared. The best score (+4) was obtained for a S. feltiae population isolated in northern Israel. These results will be used for the utilization of the new population as a biological control agent.

Genetic improvement of the desiccation tolerance and host-seeking ability of the entomopathogenic nematode Steinernema feltiae

“…In the present study, we successfully enhanced desiccation tolerance and host-seeking ability. In a previous study, Salame et al (2010) characterized the desiccation tolerance and downward dispersal of the populations that were used to establish the HFP. For all of the selected traits, the selected populations performed better than the bestperforming steinernematid populations in the previous study (Salame et al 2010).…”

“…This is probably due to the high heterogeneity of the initial population. The initial hybridization of the different isolates, which were obtained from diverse environmental regions (Salame et al 2010), ensures the maintenance of fitness despite the selections. The second factor is the mild selection pressures used in the desiccation selection regimes (3-7% survival in the stress assays, Fig.…”

“…Establishment of a heterogeneous foundation population (HFP) of S. feltiae The strains of S. feltiae used to establish the HFP were isolated in different locations in Israel, as reported recently by Salame et al (2010). These diverse sites are described in Table 1.…”

“…Selection for enhanced host-seeking ability The IJs from the HFP were allowed to move through the soil and locate a target host in a sand column assay (Salame et al 2010). Plastic pipes (5 cm diam, 21 cm in height) were filled with moistened sandy soil (8% moisture w/w).…”

“…Both traits were chosen to enhance the nematode's ability to overcome environmental conditions and improve its efficacy as a biocontrol agent. In a recent survey conducted in Israel, several populations of S. feltiae were isolated and their desiccation tolerances and downward dispersal abilities in sand columns were characterized (Salame et al 2010). We used these populations and the information obtained previously about their environmental tolerances and hostseeking abilities as the basis for the establishment of a heterogeneous study population and genetic selection.…”