Effect of moisture evaporation from diatomaceous earth pellets on storage stability of<i>Steinernema glaseri</i>

Abstract

Induction of anhydrobiosis and storage stability of entomopathogenic nematodes are influenced by moisture availability. Decreasing moisture content in diatomaceous earth (DE) pellets containing the Steinernema glaseri NJ-43 strain and its effect on survival time and infectivity of the nematode were determined. Pelletisation was performed in a vortex mixer, using DE Celite® 209 as the desiccant material. Pellets were stored at room temperature (23 ± 2°C) and high relative humidity (96–100%). Nematode survival and infectivity against last instar greater wax moth, Galleria mellonella, were tested daily. Initial average and average equilibrium moisture content in pellets were 66.7% and 13.6%, respectively, and the infective juveniles mean survival time was 8.8 days. A moisture transfer model based on diffusion and evaporation was evaluated to predict moisture fluctuations within the pellets. We concluded that 84% of variation in S. glaseri infectivity on G. mellonella larvae was explained by the survival of the nematode, whereas 52% of variation in S. glaseri survival was explained by the loss of moisture from the pellets. The moisture transfer model achieved 78% reliability in predicting moisture content and fluctuations. Therefore, the mechanisms of moisture diffusion and evaporation from the surface to the surrounding atmosphere contribute significantly to moisture loss from the pellets.