Pg. 5-10 Entomopathogenic nematodes (EPNs) for the control of Lepidopteran pests in litchi orchards in south Africa

Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis occur naturally in soils throughout the world where they parasitise different life stages of various soil-inhabiting insects. The nematodes are synergistically associated with bacteria and together they kill and utilise their insect host. Infective juveniles (IJs) are the only free-living stage of nematodes found in soil and carry the bacteria in their intestines, releasing them once the body of the host is penetrated. They kill their hosts within 48 hours, can be produced commercially and can be applied with standard spraying equipment or through certain types of irrigation systems. The main interest in these nematodes is their potential as biological control agents in integrated pest management systems.

A survey is currently being undertaken in the north-eastern parts of South Africa to establish whether any endemic EPNs can be found in these areas. Soil samples were collected in litchi, macadamia, avocado, mango, granadillas and guava orchards in the different production areas. Soil samples from undisturbed natural soils were also collected. Samples were transported to the laboratory where the soil was baited with mealworms to collect EPNs from the soil. Mealworm (Tenebrio molitor) larvae showing signs of EPN infection after 7-14 days were placed on white traps to collect the EPNs. EPNs emerging from the mealworm cadavers were send to the University of Stellenbosch for DNA identification. Thirty eight samples have been collected in the Mpumalanga Province and nine in the Limpopo Province. Nine of the samples were taken from litchi orchards and three of them tested positive for entomopathogenic nematodes. The survey will continue and samples will also be taken in the production areas of KwaZulu-Natal and Eastern Cape provinces.

Summary:

• Entomopathogenic nematodes (EPNs) of genera Steinernema and Heterorhabditis naturally occur in soils worldwide where they parasitize soil-inhabiting insect stages by releasing symbiotic bacteria that kill the host within 48 hours. They can be mass-produced and applied using standard spraying or irrigation systems, making them promising biological control agents in integrated pest management.
• A survey in northeastern South Africa (Mpumalanga and Limpopo provinces) collected 47 soil samples from fruit orchards (including litchi) and undisturbed soils, finding an overall 30% recovery rate of EPNs, with a 33% positive detection rate in litchi orchards. Positive samples are undergoing DNA identification for species determination.
• In South Africa, lepidopteran pests like false codling moth and litchi moth cause economic damage to litchi fruit, and current control methods do not target their soil stages. EPNs target these soil stages, offering a novel biological control approach.
• EPN safety tests showed no harmful effects on vertebrates or non-target organisms, and local environmental conditions impact their effectiveness. The survey is part of ongoing research to find endemic EPN isolates adapted to South African environmental conditions for pest control.
• Future steps include expanding soil sampling to other provinces, conducting lab bioassays to assess EPN virulence against target pests, and field trials to evaluate the efficacy of identified nematode species and commercial products for controlling false codling moth and litchi moth in litchi orchards.