Potential of in vivo- and in vitro-cultured entomopathogenic nematodes to infect Lobesia vanillana (Lepidoptera: Tortricidae) under laboratory conditions

Abstract

The in vivo- and in vitro-cultured South African entomopathogenic nematodes (EPNs), Steinernema yirgalemense and Steinernema jeffreyense (Rhabditida: Steinernematidae), were evaluated against larvae and pupae of Lobesia vanillana in laboratory bioassays. For larvae, high mortality was observed for all treatments: In vitro-cultured S. yirgalemense (98%) performed better than S. jeffreyense (73%), while within in vivo cultures, there was no difference between nematode species (both 83%). No significant difference was detected between in vivo- and in vitro cultures of the same nematode species. The LD50 of the in vitro-cultured S. yirgalemense, the best performing species, was 7.33 nematodes per larva. Mortality by infection was established by dissecting cadavers and confirming the presence of nematodes, which was > 90% for all treatments. Within in vitro cultures, both S. yirgalemense and S. jeffreyense were able to produce a new cohort of infective juveniles from L. vanillana larvae. Pupae, however, were found to be considerably less susceptible to EPN infection. The relative success of local in vivo- and in vitro-cultured EPN species against a tortricid species in laboratory assays is encouraging for further research and development of this technology.