Desiccation survival of the entomopathogenic nematode Steinernema feltiae:: induction of anhydrobiosis

The present study describes different desiccation tolerance traits of three strains of Steinernema feltiae (IS-6, IS-15, and N8). A slow dehydration regime (pre-conditioning at 97% relative humidity [RH] for 3 days at 23 degrees C) induced a quiescent anhydrobiosis state in ail strains, which enabled them to survive at lower humidities (75% and 85% RH). The IS-6 strain isolated from the Negev desert region of Israel exhibited the best desiccation tolerance. The second best tolerance was observed in the IS-15 strain isolated from Galilee, in the northern part of Israel. The poorest tolerance was exhibited by the N8 strain, which was obtained from Germany. The higher desiccation tolerance of the IS-6 and IS-15 strains was associated with a dispersal response of the aggregated infective juveniles (IJs) at the slow dehydration regime. This allowed the coiled IJs to enter into anhydrobiosis individually, whereas the IJs of the N8 strain remained clumped together. In the present study, the IS-6 strain was chosen to determine the optimal conditions for induction into, and recovery from, anhydrobiosis. A high correlation (r = 0.875, P < 0.05) was found between the survival of individual IJs at 85% RK and the initial numbers of IJs (ranging from 70 to 7700) in the pre-conditioned clump. The same recovery rates of pre-conditioned IJs exposed to 85% RK over a period of 12 days were obtained with either direct immersion in distilled water or immersion in distilled water after 24 h exposure to 100% RH. No significant differences in virulence and ability to penetrate Tenebrio molitor larvae were observed between non-desiccated IJs and rehydrated IJs that had been pre-conditioned and desiccated for 5 days at 85% RH.