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

Abstract

Entomopathogenic nematodes (EPNs) are known as effective biological agents against soil-dwelling 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 LD50 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.