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

Anhydrobiosis is considered to be an important means of achieving storage s tability of entomopathogenic nematodes that are used in biological control. This study explored the effects of anhydrobiosis an longevity and infectiv ity of infective juveniles (IJs) of three species of entomopathogenic nemat odes Steinernema carpocapsae, Steinernema feltiae, and Steinernema riobrave at 5 and 25 degrees C. Anhydrobiosis was induced in water-dispersible gran ules (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 infectivit y of the desiccated (anhydrobiotic) Us was compared with non-desiccated IJs stored in water for different periods. Anhydrobiosis increased longevity o f S. carpocapsae IJs by 3 months and of hi, riobrave by 1 month in WG at 25 degrees C as compared with IJs stored in water. However, desiccation decre ased S. feltiae longevity at 25 degrees C and of all three species at 5 deg rees C. These results demonstrate a shelf-life of 5 months for S. carpocaps ae at 25 degrees C and 9 months at 5 degrees C in WG with over 90% IJ survi val. For S. feltiae, over 90% survival occurred only for 2 months at 25 deg rees 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 8 5% within 1 month at 5 degrees C. Induction of anhydrobiosis in WG resulted ire 85, 79 and 76% reduction in oxygen consumption by S. carpocapsae, S. f eltiae, and S. riobrave IJs, respectively. Differences in IJ longevity amon g three species in water at 25 degrees C were related both to the initial l ipid 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 harm ful effect on the IJs and/or their symbiotic bacteria. The species differen ces in IJ longevity and desiccation survival at different temperatures are discussed in relation to their foraging strategy and temperature adaptation . (C) 2000 Australian Society for Parasitology Inc. Published by Elsevier S cience Ltd. All rights reserved.