Biological characteristics of the entomopathogenic nematode Heterorhabditis sp. IS-5: A heat tolerant isolate from Israel

Entomopathogenic nematode isolate (IS-5), from under the canopy of fruit trees in the arid 'Negev' region of Israel was found to be highly tolerant to temperatures above 30°C. Morphological measurements did not distinguish this isolate from Heterorhabditis bacteriophora Poinar, 1976. However, DNA extracted from four different genotypes (Heterorhabditis sp. IS-5, HP88 and IS-3 and H. megidis HSH2) amplified with six random primers yielded products from which it was calculated that the similarity between IS-5 and HP88 was 20%, between IS-3 and HP88 85% and between IS-3 and H. megidis 15.6%. Two hours at 37°C killed 79% HP88 infective juveniles but only 18% IS-5. Eight hours at 37°C killed 87% of HP88 but only 28% of IS-5. One hour at 40°C killed all infective juveniles of the HP88 isolate but only 26% of IS-5. Heat shock treatment for 2 h at 37°C before exposure to 40°C enhanced the survival of IS-5 juveniles to 43% as compared with non heat-shocked control. At 25°C IS-5 caused 100% mortality of Galleria mellonella larvae after 36 h and HP88 after 48 h. At 30°C IS-5 caused 100% mortality in 24 h. The average number of nematodes in cadavers exposed to IS-5 and HP88 for 48 h ranged from 15 to 16.3 and 7.3 to 10.8, respectively. At 25°C both these heterorhabditid isolates produced an average of 90,000 infective juveniles per cadaver. At 30°C and 33°C yields of IS-5 increased by 10% but those of HP88 reduced by 90%. At each temperature IS-5 juveniles emerged 2-3 days earlier than HP88.