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Microbes that cause the death of insects are called insect pathogens. Our research focuses predominantly on how microbes can be used to control economically important insects that cause damage to crops. We perform research on two key groups of insect pathogens: bacteria and viruses. The microbes we use cause the death of insect pests, but are harmless to non-target organisms, such as bees, birds and mammals. This means that these microbes can be used as safe, ecologically friendly pest control products.
A major thrust of our group is to perform the research required to commercialise insect pathogenic viruses and bacteria for the control of economically important agricultural pests. This thrust focuses on the integration of manufacturing technologies to enable economical, commercial-scale production of microbes that have shown good insect control potential. We also develop novel product formulations that improve the insect control abilities of our microbes. Our research is responsive to the needs of farmers locally and abroad, as conventional chemical insecticides cause severe ecological pollution and annually poison thousands of small-scale farmers. By developing ecologically friendly alternatives, local farmers and farm workers benefit by having the choice of using effective, cost-competitive insect control products that are not toxic to humans or other non-target organisms. Due to their ecological friendliness, the pest control products that we are developing will help to protect South Africa s biodiversity and encourage sustainable development. The Invertebrate Pathology and Biocontrol Laboratory has several active research projects, including the projects outlined below. 1. A The evaluation of insect pathogens and novel botanical compounds for the control of southern African malaria vectors
There are an estimated 300-500 million cases of malaria and over one million associated deaths reported each year, mostly in young children in sub-Saharan Africa. Malaria is vectored by certain species of mosquitoes. With a view to contributing to the reduction of malaria cases in Africa, we have research projects that are evaluating the use of insect pathogens and novel botanical compounds for the control of African mosquitoes. We are also evaluating ecologically friendly, genetically engineered bacteria for improved mosquito control. Recently we started using nanotechnology to improve delivery of water-insoluble insecticidal compounds to mosquito larvae. Since assessment of the potential environmental risks of a novel biopesticide is necessary before it application in the field, we have developed standardised aquatic microcosms to evaluate the target and non-target effect of biopesticides. 2. A Genotypic variation of South African baculoviruses
Baculoviruses are a large group of insect-specific, DNA viruses that are currently being studied and utilised as biopesticides for some of the most economically important pests. It is well documented that there is a high degree of both intra- and interspecies genetic variation within the baculovirus family; however, little is known about the true spectrum of variation or the key drivers of variation in baculoviruses. An understanding of this variation would allow for a greater insight into virus ecology, epidemiology and virus-host interactions as well as possibly aid in the understanding of the genetic variation seen in other economically important insect pathogens. We are using a novel, in-house developed technique that will provide more insight into the genotypic diversity of baculoviruses. 3. A Research and development of biological control agents for commercial use in bio-intensive pest control programmes (the key focus area is the development of baculovirus-based biopesticides)
We are developing baculoviruses for the control of a range of insect pests on horticultural crops such as tomatoes and citrus. The general objectives of the project are to research and develop biocontrol products that are: cost-competitive substitutes to conventional chemical insecticides; have similar efficacy and potency to conventional chemical insecticides; easy-to-use and environmentally friendly. In order to realise the above general objectives the project has the following set of specific objectives:
- Product development: Research and development of indigenous biological control agents, such as baculoviruses, into biocontrol agents for the control of insect pests.
- Production process development: Research and development of fermentation/bioreactor technologies and mass-rearing technologies for the cost-effective production of high yields of biocontrol agents.
- Product formulation development: Research and development of product formulation technologies.
- Field application of product: Research and development of product application technologies.
- Field efficacy of product: Product evaluation in demonstration field trials.
The project aims to develop commercially-ready biological control agents for the control of economically important agricultural pests and disease vectors in integrated pest management programmes.
In the case of baculoviruses, the key results to date have been: (1) the isolation and characterisation of new baculoviruses (granulovirus and nucleopolyhedrovirus) genotypes, some of which are extremely virulent. (2) Determination of the susceptibility of the insect instars to the baculoviruses. (3) Multiple-concentration mortality-response assays performed on field-collected neonate larvae showed that there was a significant difference in the susceptibility of insect larvae of different geographical origin. (4) Molecular characterisation proved that each new baculovirus isolate was a distinct genotypic variant. (5) The development of mass rearing techniques and technology. (6) The development of a high-quality, cost-effective diets for rearing the insects specifically for virus production. (7) The optimisation of baculovirus yields by using multi-factorial designs and monitoring several key responses. (8) The determination of microorganisms associated with extracted virus and the effect of storage on microbial load. (9) The development and testing of novel baculovirus formulations, including suspension concentrates and wettable powder formulations. (10) The confirmation of the efficacy of the product in several greenhouse and field trials on a range of crops. 4. A Development of Bacillus thuringiensis-based biopesticides for the control of lepidopteran pests
The objective of the project is to develop biopesticides based on the soil bacterium Bacillus thuringiensis (Bt). Specific aims include the isolation and characterisation of new Bt strains, the construction of genetically modified Bt strains with increased toxicity, and the optimisation of liquid fermentation of Bt strains.
Some key research outcomes (to date): Several new Bt strains were isolated from the environment. After screening the isolates for toxicity, the strain with the best larvicidal activity was selected for additional studies. Multi-factorial experiments have been performed to develop a cost-effective base medium for production of Bt strains by fermentation. The experimentally-determined formulation resulted in good Bt spore and biomass yields in a 7.5 litre Infors bioreactor. Considering the low cost of the ingredients in the developed medium, the medium was considered ideal as the basis for further optimisation for subsequent use in commercial production. Studies have been performed to compare the growth kinetics and productivity (spore yields and biomass) of the best Bt strain to other Bt strains.
The susceptibilities of two of the most important pests in South Africa, the African bollworm (Helicoverpa armigera) and the False Codling Moth (Thaumatotibia leucotreta), to Bt Cry proteins were investigated and local benchmarks for Bt Cry protein toxicity to these pests have been established. The most toxic Cry proteins were identified and formed the basis of subsequent recombinant research.
The development of recombinant DNA techniques has made it possible to significantly improve the efficacy (insecticidal activity) of the Bt strains currently used as biopesticides. The focus of this part of the project has been primarily on constructing new genetically engineered recombinant Bt strains that have either an optimised larvicidal activity against a given insect pest or a broadened toxicity spectrum. Many aspects have been investigated, including: how to select the best insecticidal gene or a combination of genes for cloning; how to increase the production of insecticidal proteins without having a negative effect on the growth rate of the Bt host; and how to introduce and maintain cloned insecticidal genes in the Bt host by a stable and efficient transfer system.
Several unique Bt-Escherichia coli shuttle vectors have been developed. An integral part of the vector strategy is the incorporation of transposon components, which facilitate recombination in compatible Bt strains and allow the in vivo removal of antibiotic marker genes. The recombination-enabled vectors thus allow the construction of antibiotic marker-free recombinant Bt strains. In order to improve expression of cry genes in recombinant strains, the effect of different promoters and ancillary proteins on Cry production has been evaluated in detail.
Field trials of novel formulations of the Bt strain with the best larvicidal activity has resulted in excellent control of economically important insect pests. Some interesting completed projects include:
- Studies on polydnaviruses in South African endoparasitic wasps.
- Evaluation of Bacillus thuringiensis and baculoviruses as potential control agents of Eldana saccharina Walker (Lepidoptera: Pyralidae).
- The isolation and characterisation of endophytic bacteria from plants and their use in biological control programmes.
- Development of in vitro assays for high throughput screening of the mammalian toxicity of botanical pesticides.
- Improved assays for the detection of Bacillus thuringiensis ?-exotoxin.
- Characterisation of the cellular immune response of sugarcane borer (Eldana saccharina) larvae.
- Evaluation of the sublethal effects of baculoviruses on insects.
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