South Africa, Using Nematodes for Bioinsecticides

Bioinsecticide are biodegradable (environment friendly), non toxic and cost effective. Some of these bioinsecticide, introduced in the USA in 1950's, are based on Bacillus thuringiensis. Bioinsecticides are a highly desirable alternative to conventional chemical-based insecticides. Bioinsecticides are environmentally friendly, compatible with other pest control agents and are also commercially viable.

Entomopathogenic nematodes (EPNs) are being recognised as important biological control agents for a wide variety of insect pests. EPNs are insect-parasitic nematodes. Like all nematodes, they are simple roundworms with long, cylindrical shaped bodies. EPNs are small nematodes, ranging in length from 0.4mm to 1.1mm. There are many attributes that make EPNs commercially suitable as biological control agents of insect pests. They have a host range that includes the majority of insect orders and families and they kill their host within 48 hours of infection. In addition, they can be easily cultured on a large scale on artificial media (in vitro culture) and the infective juvenile stage obtained from in vitro culture can be stored for long periods of time. Finally, and possibly most importantly, the infective juvenile stage can withstand high pressures and thus can be applied in the field using conventional spray application procedures.

EPN-based bioinsecticides will have many advantages over currently used chemical insecticides. Most importantly there will be a reduction in the social costs that incur from the accumulation of chemical insecticides in the food chain and in ground water. The use of such bioinsecticides will also greatly reduce the farmworker health risks associated with the application of chemical insecticides.

Entomopathogenic nematode (EPN)-based bioinsecticides have the potential for commercialisation in South Africa since indigenous EPNs can be mass- produced at low cost. Only indigenous EPNs will be used to develop EPN-based bioinsecticides and these bioinsecticides will only be sold to the South African market. Indigenous EPNs are suited for the control of local insect pests because they are adapted to local environmental conditions and are natural regulators of insect populations.

The broad activity of an EPN-based bioinsecticide allows for the target of several markets. Such a bioinsecticide will control insect pest communities that occupy the subterranean and semi-subterranean zone during at least one part of their life-cycle. All vegetable and fruit farmers as well as maize, wheat, sugarcane, cotton and groundnut farmers in South Africa can benefit from EPN-based bioinsecticides. Commercial golf course greens-keepers are also a potential market.

A number of indigenous EPN strains have already been isolated during Sarah's Masters research. These strains were isolated from soil samples collected within South Africa. Once a soil sample is obtained, larvae from the Greater Waxmoth (Galleria mellonella) are place in the soil. Any dead larvae are removed from the soil seven days later. If the larvae have been infected with entomopathogenic nematodes, the infective juvenile stage of the nematode will begin emerging from the dead larvae. These juveniles are collected and stored temporarily in water. The life cycle of entomopathogenic nematodes begins with the infective juvenile stage. The infective juvenile is the only stage of the lifecycle that is adapted to survive in the environment (usually soil) for an extended length of time. They remain in this free-living state until they locate a suitable host.

At least two of the already isolated strains have the potential for development as bioinsecticides. They are highly pathogenic strains and thus have been cultured with ease in the laboratory.

A number of steps are first required before commercialisation and appearance of these and other nematode strains as bioinsecticides on the market. Firstly, laboratory based screening trials of the nematode strains against a range of insect pests will be performed. Field based screening trials will then be conducted using those nematode strains showing the most potential for successful biological control. Following this, a pilot production plant is to be set up for the mass production of the nematode strains that have passed the screening trails. In conjunction with this, nematode storage systems, the best transport method and several application technologies will be designed and tested. The final step in the commercialisation process will be large-scale field trial applications of the selected entomopathogenic nematode strains.

Source: Sarah Taylor, WITS University