Significant progress has been made to commercialise a local EPN isolate – a potential biopesticide product. By Prof Antoinette Malan and Dr Murray Dunn
After many years of research, and with funding support from the main industries (citrus, deciduous fruit, and grapes), significant progress has been made to commercialise a local entomopathogenic nematode (EPN) isolate that has the potential to be used as a biopesticide product.
EPNs are multicellular organisms, or more precisely, microscopic round worms, which offer an environmentally friendly "tool" for pest management in crops.
Although their effect is not as dramatic as that of chemicals, EPNs are highly effective in the soil environment, because they deliver a continuous ecosystem service in the background by the prevention of flare-ups of key insect pests and supress sporadic insect pest problems. Numerous local and international studies have demonstrated their efficacy against a wide variety of insect pests. Benefits of EPNs are that they are non-toxic to the environment, safe to handle and have only a negligible impact on nontarget insects. Thus, they offer a sustainable pest control option; a case of using nature to fight nature.
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What we've done so far
- Starting from a baseline of no nematodes and no knowledge, we have trapped EPNs in soil samples taken from orchards and natural vegetation. In the process, we have discovered the incredible extent of local microorganism biodiversity, with the description of 12 new species of EPN bearing South African names such as Steinernema khoisanae, S. bakwenae, Heterorhabditis noenieputensis and H. safricana. We used all isolated EPN species to test their efficacy against our key insect pests. In the process, a star nematode, called Steinernema yirgalemense, was identified as being the most effective against our most important insect pests, with its performance being on par with that of other internationally well studied species.
- The nematodes were tested in semi-field trials with them, in some cases, delivering surprisingly better results than expected, especially in the case of false codling moth (FCM).
- We have provided a proof of concept that, with liquid mass-culture of EPNs, it is commercially viable for large-scale production, first in glass flasks and then upscaled to desktop bioreactors. In addition to the technological know-how being easily transferable to students working on new projects, we were also able to supply mass-cultured, formulated nematodes for SATI- and Hortgro-sponsored projects, including field trials for the control of both FCM and weevils.
- We have proven, up to a certain stage, that it is possible to mass-culture nematodes in desktop bioreactors, in a way that is comparable to industrial commercialisation.
What's still required
If EPNs are as competent at insect pest control as researchers claim they are, where are they? Why do we not have a local product that is available to South African producers? The answer is quite simple, really: Too few can yet be produced, with such a situation having been the case for at least the past decade. Although, globally, scientists and industry players have for almost three decades, known of the enormous commercial potential that EPNs have as a sustainable pest control agent. However, producing them in sufficient numbers to match demand has been a challenge.
EPNs can be produced in a multiplicity of ways. Labour costs decrease in tandem with an increase in both the use of advanced technologies and the number of nematodes produced. While this becomes more cost-effective, the risk of things going wrong increases. Nematodes can be cultured in insects, a relatively easy but most labour-intensive way of producing high-quality nematodes. They can also be cultured artificially on a medium that mimics the insect environment (liquid culture, see Figure 1).
This includes the culture of nematodes in the laboratory in glass flasks or in engineering intense, high-cost bioreactors. Although we know how to produce EPNs for commercial purposes, we have only done so at a small scale in desktop bioreactors and the scale-up process is notoriously challenging. We believe that industry support will be required to identify a suitable commercialisation model.
It is recommended that future research should be directed towards developing the production of multiple species, focusing on EPN behaviour after application, and attaining EPN compatibility with other agricultural-input products.
Instead of applying nematodes inundatively to control a specific insect pest, they could also be used in many ways to benefit soil health. This includes being applied by means of inoculation to orchards, where they have previously been killed off through chemical use against plant-parasitic nematodes. Some orchards have, in fact, been found to have a natural high residential natural population of EPNs. High populations of nematodes in orchards can also be managed by means of, e.g., supplying them with such susceptible host insects buried in cages, or by way of managing the ground cover of the vineyard or orchard floor.
A proof of concept has been established, with clear-cut evidence of research showing the potential of EPNs.
