Anhydrobiotic potential and long-term storage of entomopathogenic nematodes (Rhabditida: Steinernematidae)

Anhydrobiosis is considered to be an important means of achieving storage stability of entomopathogenic nematodes that are used in biological control. This study explored the effects of anhydrobiosis on longevity and infectivity of infective juveniles (IJs) of three species of entomopathogenic nematodes Steinernema carpocapsae, Steinernema feltiae, and Steinernema riobrave at 5 and 25 degrees C. Anhydrobiosis was induced in water-dispersible granules (WG) at 0.966-0.971 water activity and 25 degrees C following a 7-day preconditioning of IJs at 5 degrees C in tap water. Survival and infectivity of the desiccated (anhydrobiotic) IJs was compared with non-desiccated IJs stored in water for different periods. Anhydrobiosis increased longevity of S. carpocapsae IJs by 3 months and of S. riobrave by 1 month in WG at 25 degrees C as compared with IJs stored in water. However, desiccation decreased S. feltiae longevity at 25 degrees C and of all three species at 5 degrees C. These results demonstrate a shelf-life of 5 months for S. carpocapsae at 25 degrees C and 9 months at 5 degrees C in WG with over 90% IJ survival. For S. feltiae, over 90% survival occurred only for 2 months at 25 degrees C and 5 months at 5 degrees C in WG. Steinernema riobrave had over 90% survival only for 1 month at 25 degrees C and the survival dropped below 85% within 1 month at 5 degrees C. Induction of anhydrobiosis in WG resulted in 85, 79 and 76% reduction in oxygen consumption by S. carpocapsae, S. feltiae, and S. riobrave IJs, respectively. Differences in IJ longevity among three species in water at 25 degrees C were related both to the initial lipid content and the rate of lipid utilisation, but not at 5 degrees C. The one-on-one infection bioassays indicated that desiccation had no negative effect on the infectivity of any of the nematode species suggesting no harmful effect on the IJs and/or their symbiotic bacteria. The species differences in IJ longevity and desiccation survival at different temperatures are discussed in relation to their foraging strategy and temperature adaptation.