Effect of moisture evaporation from diatomaceous earth pellets on storage stability ofSteinernema glaseri

Abstract

A c c e p t e d M a n u s c r i p t 2 Induction of anhydrobiosis and storage stability of entomopathogenic nematodes are influenced by moisture availability. Decreasing moisture content in diatomaceous earth pellets containing Steinernema glaseri NJ-43 strain and its effect on survival time and infectivity of the nematode was determined. Pelletisation was performed in a vortex mixer, using diatomaceous earth Celite ® 209 as 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 IJ's 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.

Moisture Evaporation from Granular Biopesticides Containing Quiescent Entomopathogenic Nematodes

“…The main phenomenon that governs the functional performance of the GBs is that if the rate of water reduction from their structure is optimal, the IJs are properly desiccated at a suitable rate and their storage stability is increased [1]. In laboratory, it has been found that the removal of moisture content from pellets by evaporation is well related to the survival of the IJs (Pearson r = 0.725) and infectivity on Galleria mellonella larvae (Pearson r = 0.904), suggesting that the relationship between the pellet drying rate and the storage stability may be an important factor to improve the shelf life of GBs containing Steinernema glaseri IJs [3].…”

“…In the most successful case, S. carpocapsae IJs survived up to 7 months ( Figure 2) and maintained their infectivity on G. mellonella above 70% in water dispersible granules (WDG) stored at 25 C,whosemoistureisreducedatarateof8.26 Â 10 À7 %s À1 [13,15]. In the less successful case S. glaseri IJs survived 8 days and maintained its infectivity on G. mellonella above 80% in diatomaceous earth pellets ( Figure 3)s t o r e d at 23 AE 3 C, whose rate of pellet moisture reduction is 6.134 Â 10 À5 %s À1 [3]. This reduced shelf life at room temperature limits their commercial exploitation, especially if GBs contain S. glaseri IJs and if these are compared with the long shelf life of commercial chemical pesticides.…”

“…Recently, it has been found that the drying kinetics of pellets is reproduced by a surface evaporation model [7] with a percent relative average deviation value of 21.95%; consequently, there is room for improvement through the proposed simplifying assumptions, but they need to be determined experimentally and expressed in mathematical form to feedback the model [3]. But, to improve this theoretical approach, it is necessary as first step to understand the water migration by evaporation from GBs towards the surrounding atmosphere and its variation factors.…”

Formulation of entomopathogenic nematodes for crop pest control - a review

“…Anhydrobiosis is considered as an important means of achieving the storage stability of entomopathogenic nematodes and is defined as a reversible and physiologically arrested state of dormancy induced by dehydration (Barrett 1991;Grewal 2000b;Grewal et al 2006). Thus, moisture content and moisture loss rate of the pellets are essential research topics to enhance the storage stability of pellet formulations under conditions of room temperature and for retaining the biological control abilities of the EPNs (Grewal & Peters 2005;Perry et al 2012;Cortés-Martínez et al 2016).…”

“…They proposed the mechanisation of the pellet production process. Finally, Cortés-Martínez et al (2016) evaluated the effect of moisture evaporation from the diatomaceous earth pellets on the survival time and infectivity of s. glaseri stored at room temperature and high relative humidity. Also, they evaluated a moisture transfer model by diffusion and evaporation to describe the temporal behaviour of moisture content in diatomaceous earth pellets.…”