A novel method for long-term storage of the entomopathogenic nematode Steinernema feltiae at room temperature

A novel method was developed for long-term storage of infective juveniles (IJs) of the entomopathogenic nematode (EPN) Steinernema feltiae IS-6 at 23 ± 0.3 °C. A nematode suspension in distilled water containing 18% glycerol and 2% sodium alginate was dropped in 0.5% CaCO3 · 2H2O, which formed calcium alginate granules. The granules were placed in 5-cm petri dishes and transferred into sealed 2.5-L desiccators under 100 or 85% relative humudity (RH), or sealed into plastic boxes in which a high RH was maintained by the presence of a piece of distilled water-soaked sponge. The experimental results showed that after storage for 6 months at 23 °C, the survival rates of nematodes in the granules in the desiccator at 100% RH and in the plastic box were 99.8 ± 0.4 and 95.9 ± 4.3%, respectively. Under the same conditions, the survival rates of nematodes stored in distilled water and in granules without osmotic solution were 10.3 ± 1.9 and 14.7 ± 4.7%, respectively. EPNs stored in the desiccator at 85% RH were all dead after 4 months. The infectivity, as measured by insect mortality (100%) and invasion rate (23.5 ± 1.6%) of osmotically desiccated nematodes in granules that had been stored for 6 months in the desiccator at 100% RH was similar to that of freshly reared ones. In contrast, the invasion rates of nematodes stored in either distilled water or in granules without osmotic pressure were zero, and the invasion rate of the nematodes in granules stored in plastic boxes was 1.7 ± 0.2%.