Formulation of South African entomopathogenic nematodes using alginate beads and diatomaceous earth

Abstract

Large-scale use of entomopathogenic nematodes (EPNs) (Rhabditida: Steinernematidae and Heterorhabditidae) as biological control agents is impaired by their short shelf life. Three local South African EPN species, including Steinernema yirgalemense, S. jeffreyense and Heterorhabditis bacteriophora, were investigated for their role in formulations. Encapsulation of the infective juveniles (IJs) in alginate beads and diatomaceous earth (DE) was investigated. Survival of the IJs in the formulations was determined at 6 °C, 14 °C and 25 °C for four weeks. Of the IJs, 10-20% were observed to escape from the beads, depending on temperature, and readily survived the encapsulation process. DE did not cause the desiccation of the nematodes, with there still being a lower mortality rate by the 4th week of the study. In both formulations, the survival and virulence rates differed significantly at 6 °C, as compared to at 14 °C and 25 °C, with a drastic decrease over time for S. yirgalemense. The EPN species revealed poor survival and loss of virulence at low temperatures in both formulations. The alginate beads successfully retained most of the IJs and can be stored for a longer time.