Effects of abiotic factors on the osmotic response of alginate-formulated entomopathogenic nematode, Heterorhabditis bacteriophora (Nematoda: Rhabditida)

Limited shelf life of entomopathogenic nematodes severely restricts their use in biological control programs. In a series of experiments, the dehydration and rehydration response of Heterorhabditis bacteriophora infective juveniles (IJs) was investigated under a range of glycerol concentrations, temperatures and incubation periods. Based on the outcome of these initial studies, nematodes dehydrated using the optimal process were formulated in alginate granules to understand how these nematodes would undergo survival formulation in a model carrier. The highest rate of osmotically arrested IJs occurred in the 22% glycerol solution (98.06%). IJ recovery was considerably improved when dehydration was processed at 10% glycerol solution and 15°C. By trapping IJs in calcium alginate, depending on the adjuvants, the survival rate of IJs differed significantly. IJ state (dehydrated or non-dehydrated) and the addition of formaldehyde had a profound effect on IJ viability, though the severity of the effect varied was dependent on whether the IJs were alginate formulated. Among different formulations, the highest viability (84.18%) was observed where dehydrated IJs were formulated in alginate granules containing formaldehyde. The results showed that the concentration of osmotic solution not only determines the percentage of dehydrated IJs but also affect their subsequent recovery in an aqueous environment. Overall, the results indicate that the shelf life of formulated IJs is significantly affected by combination effects of a broad range of factors. Then understanding the interactive mode of actions of involved factors in formulation play a critical role in developing and introducing more efficient formulations.