Poinar, G. O., Jr.; Smits, P. H.

The present study describes specific identification and characterization of the biological activity of entomopathogenic nematodes which were isolated from soil samples in a recent survey of the arid "Negev" region of Israel. Morphological examination indicated that the nematode populations designated IS₁, IS₂ and IS₃ represent strains of Heterorhabditis bacteriophora. Whereas IS₄ is considered a strain of H. megidis. The identification for IS_-3 and IS₄ isolates was confirmed by analysis of total DNA on restriction fragment length differences of repetitive sequences, while the IS₂ and IS₃ isolates showed banding pattern different from that of H. bacteriophora. In infectivity assays the IS₄ strain of H. bacteriophora was found to be the most pathogenic of the 4 new population and the HP 88 strain of H. bacteriophora against the lepidopteran species Galleria mellonella, Earias insulana and Spodoptera littoralis. IS₄ infectivity to the lepidopteran strain was equivalent to that of Steinernema carpocapsae A11 strain. The superior infectivity of the IS₄ was also demonstrated against the scarab Maladera matrida. Viability of the H. bacteriophora HP 88 infective juveniles was reduced to 20% when exposed to 37°C for 3 h. The level of survival of all other heterorhabditids strains was 3- to 4.5-fold higher than the HP 88 strain. The viability of S. carpocapsae A11 strain was not affected by the same heat treatment. Exposure to low relative humidity conditions (3 h at 50-60% RH) resulted in 55-85% reduction in most of the various nematode populations. Relatively high tolerance to the desiccation conditions was recorded with the IS₁ and IS₃ heterorhabditid isolates.