Investigating the potential of South African Entomopathogenic nematodes for the management of Ceratitis capitata (Wiedemann)

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), hereafter known as the medfly, is one of the most economically important pests affecting fruit production worldwide and remains a persistent challenge in South Africa’s export-orientated horticulture sector. Its high reproductive potential and wide host range make it challenging to manage through conventional strategies alone. Increasing regulatory pressure, pesticide resistance and the environmental damage associated with synthetic chemicals highlight the need for alternative, sustainable management options that can be integrated into existing integrated pest management (IPM) programs. Among the most promising management options are entomopathogenic nematodes (EPNs), particularly locally adapted species which may have enhanced field performance. However, despite South Africa’s rich EPN diversity, very limited research has evaluated the efficacy of local isolates against C. capitata, especially across key life stages and soil environments. This study assessed the infectivity and persistence of two indigenous EPN isolates, Heterorhabditis bacteriophora SGI-170 and Steinernema yirgalemense 157-C, against medfly larvae, pupae of different ages, and emerging adults. The initial screening demonstrated that third instar larvae were the most susceptible stage, with H. bacteriophora achieving the highest mean infection rate. Pupae were largely resistant to infection, with consistently low infection levels across all age groups for both species. Notably, emerging adults became infected when moving through the EPN-treated soil, especially with increased dosage, indicating an additional and underexplored infection opportunity. To examine their persistence under more realistic conditions, EPNs were evaluated across multiple South African soils collected from farms. The study evaluated a range of soil textures, from sandy soils to those with increased clay content, and monitored EPN activity and persistence over a six-week period. Soil texture significantly influenced infectivity, with both isolates showing better infectivity and persistence in the sandy soils, with a marked decline in performance in the soils with increased clay content. This was likely due to restricted movement, altered water distribution, and reduced aeration in the clay-rich soils. Nonetheless, H. bacteriophora SGI-170 maintained a higher infection rate across all soil textures and time intervals compared to S. yirgalemense 157-C, highlighting the strong potential of this isolate. The persistence patterns also provided insight into moisture suitability, showing that the standardised 10% (v/v) moisture level disproportionally limited EPN activity in the clay-rich soils while supporting optimal conditions in the sandy soil. Overall, the results indicate that local South African isolates, especially H. bacteriophora SGI-170, have strong potential as biological control agents targeting the soil-dwelling stages of the medfly. Their ability to infect third instar larvae and emerging adults, combined with multi-week persistence in favourable soils, provides strong support for their incorporation into existing IPM programs. Future research should explore species-specific recycling conditions, quantify the effect of soil moisture on infectivity in different soil textures, and quantify the effect of natural EPN recycling on their persistence.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Wimbush, Richard Dillon

Advisors dc:contributor.advisor

• Addison, Pia
• Bekker, Gulu
• Malan, Antoinette

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/135549

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/135549