Entomopathogenic nematodes from north-eastern South Africa and their virulence against false codling moth, Thaumatotibia leucotreta (Lepidoptera: Tortricidae)

摘要

A survey was undertaken to determine the diversity and frequency of endemic entomopathogenic nematodes (EPN) in subtropical regions in the Mpumalanga, Limpopo and KwaZulu-Natal provinces of South Africa. A total of 136 soil samples were randomly taken from cultivated and uncultivated habitats, including subtropical fruit tree orchards (avocado, litchi, macadamia, mango and guava) and adjoining natural vegetation. EPNs were isolated from 14 samples (10.3%) by means of baiting with Tenebrio molitor larvae. Heterorhabditis was the most common genus isolated from 12 samples, whereas only two Steinernema species were isolated. The most common Heterorhabditis isolated were Heterorhabditis noenieputensis and H. zealandica, which were both isolated from four samples each. The present report is the first occurrence of H. taysearae and H. baujardi in South Africa. The two Steinernema species are both unknown species. Laboratory bioassays were conducted to determine the potential of seven native EPN isolates to control the false codling moth (Thaumatotibia leucotreta) (FCM). Last instar FCM larvae were found to be most susceptible to S. yirgalemense (157-C), H. zealandica (WS 23) and Steinernema litchii (WS9), when exposed to 50 IJs/50 mu l water for 48 h, causing 100%, 94.2% and 93.5% mortality, respectively.