Abstract
Entomopathogenic nematodes (EPNs) are microscopic roundworms that are found in soil worldwide. They deliver an important ecosystem service through preventing natural flares in insect reproduction by means of utilising the soil stages of insects as a food source and by acting as natural biocontrol agents. A survey of EPNs was conducted in the JS Marais Nature Reserve, Stellenbosch, in the Western Cape province of South Africa. Soil samples were baited with the larvae of three susceptible hosts, codling moth (Cydia pomonella), wax moth (Galleria mellonella) and mealworm (Tenebrio molitor) to determine the presence of EPN. Of the 76 soil samples collected across the reserve, 39 were found to be positive for the presence of EPN (51.32%). Among the positive samples, 87% contained Steinernema isolates, 8% contained Heterorhabditis and 5% contained the Oscheius sp. Morphological and molecular studies were performed to characterise the isolates to species level. The Steinernema species were identified as Steinernema khoisanae in 34 samples, and as Steinernema nguyeni in five samples. The only species of Heterorhabditis found was H. safricana, which was identified from three samples. An unknown Oscheius sp. was found in two samples. The reserve’s population of S. khoisanae showed interesting inter-individual variation (93%) early in the internal transcribe spacer (ITS) region, leading to short single-usable sequences, which, in most cases, included only the ITS1 or ITS2 region. However, using the D2D3 confirmed their identity as S. khoisanae, with such occurring in all areas and soil types of the reserve.Conservation implications: The undisturbed alluvial fynbos and renosterveld of the JS Marais Nature Reserve showed high EPN abundance and diversity in stark contrast to the agro-ecosystems present in the Cape floristic region. This finding, on a micro level, should be conserved for future bioprospecting in the fynbos for EPNs with potential as biocontrol agents.
Highlights
Entomopathogenic nematodes (EPNs) in the families Steinernematidae and Heterorhabditidae are of great interest because of their potential as commercial biological control agents against insects
The occurrence and diversity of the EPNs found in the JS Marais Nature Reserve were high (51%), with four species being identified, namely S. khoisanae, S. nguyeni, H. safricana and an Oscheius sp
The Steinernema spp. were more abundant than the others, which is found in 94% of the positive samples
Summary
Entomopathogenic nematodes (EPNs) in the families Steinernematidae and Heterorhabditidae are of great interest because of their potential as commercial biological control agents against insects. The study of natural EPN occurrence and distribution, as characterised by different ecological habitats in various geographical areas, provides baseline information for incorporating the pathogens in biological control programmes, and for understanding the complexities of their biodiversity. The factors such as geographical location, climatic conditions, soil properties and habitat type may determine the occurrence and distribution of the EPNs. To be effective as biological control agents, EPNs need to be adapted to the local environmental conditions of the site of application (Bedding 1990). With inundative application, with an immediate effect on the target organism, temperature and humidity are the most important environmental factors to take into consideration
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