Virulence and survival of native entomopathogenic nematodes for the management of white grubs in South Africa

Abstract

Entomopathogenic nematodes (EPNs) provide a potential alternative to chemical insecticides to control root-feeding pests of agricultural and forestry crops. One of the challenges in using EPNs in these environments is low post-application survival. We evaluated the survival of infective juveniles (IJs) of four EPN species (Heterorhabditis bacteriophora, H. baujardi, Steinernema sacchari and S. yirgalemense) in three different substrates for application. Survival of IJs was assessed directly by counting living IJs and indirectly by baiting with Galleria mellonella larvae. The virulence of different native and non-native EPNs against the third-instar larvae of Heteronychus licas, an important soil-insect pest of agricultural crops in South Africa, was also tested. Nematode survival was highest in a gel medium, followed by a gel-soil mixture, and lowest in soil. Survival of Steinernema species was higher than Heterorhabditis species when considering direct nematode counts, but these results were not consistent when using wax moth mortality as a proxy for survival. The South African strain of H. bacteriophora gave the highest and most rapid levels of mortality in H. licas grubs, followed by a commercially applied strain of H. bacteriophora. The results suggest that native EPNs could provide an option for soil-insect management in South Africa and provide insights into effective means of application.