Desiccation survival of entomopathogenic nematodes of the genus Heterorhabditis

The present study aims at determining the desiccation tolerance of entomopa thogenic nematodes from the genus Heterorhabditis recently isolated in Isra el. We first verified the most suitable desiccation conditions that lead to induction of the anhydrobiotic state using Heterorhabditis bacteriophora H P88. After direct exposure of infective juveniles (IJs) to 97% and 93% r.h. for 96 h, the survival rate was > 70%. By contrast, exposing HP88 IJs to 8 8% and 85% r.h, resulted in poor survival (< 10%) or complete mortality. Fo llowing exposure to 97% and 93% r.h. for 24, 48, 72 or 96 h, survival range d from 68% to 79% with no significant differences between the exposure peri ods. Stepwise reduction of r.h. conditions (97% > 93% > 88% > 85% r.h.) at a 24-h or 72-h interval resulted in enhanced survival (30% survival) of IJs at the final r.h. level compared with IJs which were either directly expos ed to 85% r.h. (0% survival) or were preconditioned at the higher r.h. leve ls prior to exposure to 85% r.h. (15% survival). H. bacteriophora HP88 IJs were able to survive for at least 18 days after preconditioning. Al 97% r.h . nematode viability remained stable at 70-85% and at 93%, r.h. survival ra nged between 37% and 60%. The data indicate that survival is influenced by rate of water removal from the nematode's body and a minimal relative humid ity level (>93%). Substantial differences in survival ability were observed among IJs of 12 new heterorhabditid populations, isolated from different c limatic regions in Israel, which were preconditioned at 97% r.h. for 72 h f ollowing by an additional 72 h at 93% r.h. Maximum survival was recorded wi th HIS-19 (64%), moderate (40-55%) survival was observed with seven isolate s, including H. bacteriophora HP88, and five isolates displayed poor (<25%) desiccation tolerance.