Australasian Biotechnology (backfiles) AusBiotech ISSN: 1036-7128 Vol. 6, Num. 4, 1996

Australasian Biotechnology,
Volume 6 Number 4, July/August 1996, pp.218- 221

Microbial Biopesticides and Integrated Pest Management,

D.G. Holdom, C.J. Monsour, R.E. Teakle, D.J. Rogers and M.P. Walton,

Cooperative Research Centre for Tropical Pest Management, Gehrmann Laboratories, University of Queensland, Qld 4072

Code Number: AU96007
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Increasing environmental, regulatory and market pressures, along with increasing pest resistance, are dictating a progressive move away from chemicals for insect pest control. Insect pathogens (viruses, bacteria, fungi and nematodes), produced artificially and formulated into microbial biopesticides, can provide part of the answer, both as alternatives to chemicals and as components of resistance management strategies. While the large markets, particularly for Bacillus thuringiensis, are dominated by large multinationals, there is considerable scope for local producers to target regional and niche markets.

The development of microbial pesticides requires research into production, formulation, application and adoption issues for each product. The Cooperative Research Centre (CRC)for Tropical Pest Management has research interests in initial development, application strategies and adoption of microbial biopesticides in integrated pest management programs. Collaborative programs involving potential producers with expertise in medium and large scale production, and users are essential for the long-term success of biopesticides. The CRC concept is well suited to such collaborative research.

Introduction

Increasing concerns in recent years about human health and environmental problems due to chemical pesticides, coupled with increasing pest resistance to chemicals, have led to a reappraisal of our approach to controlling pests and diseases in crops. The trend now is towards a management concept in which the best available combinations of tools are used to manage pests below economic thresholds with minimal risks to human health and the environment. Thus the emphasis is on management, and pest management is simply one component of growers' overall crop management systems. (Foster et al., 1994; Brough et al., 1995). Integrated pest management (IPM) is the term usually given to this approach.

Insect pathogens constitute a group of potentially valuable IPM tools which are selective and generally safe to the environment. They can cause spectacular pest fatalities resulting in virtual elimination of insect populations, but because they are passively distributed, and insects are small targets, naturally occurring insect pathogens frequently arrive too late, or spread too slowly, to provide effective control. This is especially true in cropping environments, where frequent disturbance prevents the pathogen inoculum from building up. Microbial biopesticides are an approach to overcoming these limitations.

Microbial biopesticides are insect pathogens which have been produced artificially and formulated for application to crops. The idea is to be able to apply them with much the same equipment as is used for chemical pesticides. They may be used as alternatives to chemicals where these either no longer work or are unacceptable, or may be used along with chemical pesticides as part of resistance management strategies. For instance, microbial pesticides might be used routinely, with chemicals remaining for emergency use, or as part of a rotational schedule with chemicals. The idea behind this approach is that by exposing pests to a range of different mortality factors, resistance to any single one is much less likely. In addition, the selective nature of microbial pesticides leaves other natural enemies still operating. However, microbial biopesticides are not "magic bullets", or panaceas, any more than chemical pesticides have turned out to be.

The purpose of this article is to outline some of the issues involved in the development and use of microbial biopesticides. The discussion relates mainly to wild-type organisms, though most of the issues also apply to transgenic organisms.

Development of Microbial Biopesticides

Early attempts to produce and use microbial biopesticides were based on an inadequate understanding of the requirements for successful development and implementation. For this reason, results were often inconsistent, and the reputation of these products suffered accordingly, with few reaching commercialisation, and even fewer succeeding in the marketplace. It is now understood that all aspects of microbial pesticide production, formulation and use require careful investigation. The process of developing a microbial pesticide involves (in simple terms) strain selection and testing, development of suitable production techniques and formulations, and field evaluation. Toxicity and residue testing for registration purposes are also required, but they are generally much less rigorous than are required for chemicals, owing to the intrinsic safety of many pathogens, which are ubiquitous, naturally occurring organisms (Taverner, 1995; Pitt, 1995). There is a trend towards exemption from many requirements for at least some non-transgenic microbial pesticides. This generally means that the registration process, especially for non-transgenic insect pathogens is much less expensive than for chemicals.

Whitten (1995) pointed out that the "conventional commercial model of large multinational companies developing and marketing pesticides may not be appropriate for the development and redeployment of biopesticides. Networking and cottage industries could become the hallmark of the biopesticide industry." This may in part be true, but we believe there will be a role for many levels of commercial involvement. The big change is that there are likely to be increasing opportunities for smaller companies offering flexible production for local and niche markets, such as high-value horticultural crops, forest nurseries and mosquito control.

Production

Production systems will have to be tailored to individual pathogens. For example, at present, insect- viruses can only be produced in live insects, a labour intensive process. Recent developments in production in cell cultures may make this a viable option in the future (Chakraborty et al., 1995). Whereas production of viruses in insects is possible at the cottage industry level (quality control problems notwithstanding), production in cell cultures requires sophisticated fermentation facilities and a high level of expertise.

Fungi and nematodes are traditionally produced on solid substrates using relatively low technology and simple substrates such as grain. Increasingly sophisticated production methods are now being developed, including liquid fermentation and twostage fermentation processes (Feng et al., 1994). Methods such as nutrient-impregnated granules offering a large surface area within a relatively small volume have also been developed for production of fungi (Desgranges et al., 1993). A better understanding of the nutrient requirements of all the pathogens is needed, but this knowledge is steadily increasing.

While production on simple substrates requires fairly simple technology, and is applicable in cottage industry environments, more sophisticated production systems requiring more capital and expertise are likely to lead to higher quality and more consistent products. This is because produc- tion conditions strongly influence both the survival (in storage and in the field) and potency of the microbial pesticide (e.g. Lane et al., 1991). It is this factor which may mitigate against the "cottage industry" approach. Furthermore, various attempts at producing biopesticides have shown that quality control can be a problem, particularly in unsophisticated production environments. Both contaminants and unintentional variations in growth conditions increase the variability and hence reduce the reliability of the end products, leading to a loss of confidence on the part of users.

Bacillus thuringiensis (Bt) production is dominated by large corporations with major fermentation capacity, notably Abbott Laboratories, Novo Nordisk, and Sandoz (Lisansky, 1995), but there are also smaller producers such as Ecogen and Mycogen Corporations. These companies produce strains for use against major pest groups, notably Lepidoptera (caterpillars), Coleoptera (beetles) and mosquitoes. A wide variety of Bt strains with different activities are known and undoubtedly many more strains of this ubiquitous bacterium remain to be discovered. Production opportunities within Australia are likely to be initially with specialist local and niche markets, though as the wealth and sophistication of markets in Asia increase, export opportunities are also likely to increase. Even though Bt is basically a microbial toxin, and the bacterium is easily produced in fermenters, production conditions still strongly influence potency (Stafford, 1995), so thorough research and good quality control are essential.

Formulation

Formulation is another key area in which significant advances have been made in recent years. These have produced significant increases in the shelf life and efficacy of both Bt and fungi. Important recent developments include improved drying, with the recognition that this is the key to extending the shelf life of fungi, and the advent of oil-based formulations for ultra-low-volume application. These developments have allowed the development of fungal products capable of causing high levels of mortality to grasshoppers and locusts in hot, arid environments (Lomer and Prior, 1991).

Application and Use Strategies

Because they kill more slowly than chemicals, and often have shorter residual lives than many chemicals, timing and placement of microbial pesticides are very important. This is where collaboration between growers and field entomologists is important in developing optimal use strategies. Knowledge in this area is improving steadily.

Microbial pesticides have varying modes of action, and this influences the uses to which they may be put. Bacteria and viruses must be consumed to take effect, while fungi and nematodes can enter the insect via the cuticle (skin). Bt acts via a bacterial toxin, and is therefore not a true pathogen, while other microbial pesticides are based on true pathogens which can proliferate in the host population, infecting insects not infected at the time of application. Fungi and nematodes are the only pathogens which can be used against sucking insects such as aphids, scale insects and thrips, and may also be the only option for chewing insects which feed inside plant tissues. Because of their dependance on moisture, nematodes are limited to protected habitats, where they can be extremely effective against borers for example.

Cooperative Research for Biopesticide Development

The range of issues involved in the development of biopesticides means that a cooperative research effort will be needed. Grower input will be needed in the identification of problems, and in identifying the formulation and application strategies which are likely to be viable in the commercial context. Similarly, it will be essential to involve potential commercial producers at an early stage in order to develop commercially viable production systems. At the research level, expertise is needed in microbiology, and laboratory and field entomology. The CRC for Tropical Pest Management and affiliated scientists have expertise with bacteria, fungi and viruses, and significant field entomology experience, including the testing of microbial pesticides. Current research within the CRC for Tropical Pest Management is focussing on the use of Bt and a nuclear polyhedrosis virus (NPV) for control of heliothis caterpillars in tomatoes, corn, cotton and other crops, and the use of Metarhizium against white grubs (root feeding larvae of chafer beetles). A new project is looking at fungal pathogens for control of heliothis and cabbage moth (Plutella).

Implementation

IPM is a knowledge-intensive process. The properties and limitations of the available tools must be understood, along with the ecology of the target pest(s) and the phenology of the crop, if pest management strategies are to be truly effective. This extra complexity, added to the already complex process of crop management, and coupled with a cautious attitude to new, unproven ideas, poses challenges for adoption of microbial pesticides. On the other hand, increasing market and environmental pressures to move away from chemicals mean that growers are increasingly receptive to safer alternatives. We need to better understand grower perceptions of microbial pesticides, and move them from being receptive to the idea of using safer alternatives to chemicals, to actually using them. This is an aspect that other scientists at the CRC for Tropical Pest Management are focussing on (Foster et al., 1994; Brough et al., 1995).

Conclusions

There are likely to be opportunities for local production using a range of technologies to supply specialised markets, particularly in horticulture and floriculture, and against mosquitoes. Ultimately there may be significant export opportunities. Realisation of this potential will require a cooperative research effort with input from diverse groups including growers, scientists from a range of disciplines, production companies, and extension workers. The required cooperative research paradigm and the means of achieving this cooperation are embodied within the CRC system.

The increasing need for Australia to be a "clean, green" producer of high quality food, coupled with local concerns about our own environment, and the increasing incidence of pest resistance to chemicals, means that we will have to find alternatives to chemical pesticides at an increasing pace in the future. Microbial pesticides offer part of the answer, and because their production and use are knowledge intensive, there is a real opportunity for Australia to utilise its skills base in this area. However, the development of competitive microbial biopesticides will require a significant long-term commitment of resources from a number of organi- sations, both public and private. If this does not happen, we will remain net importers of this type of technology.

References

Brough, E., Foster, J. & Norton, G. (1995) Transgenic plants: A challenge to integrated pest management. Australas. Biotechnol. 5: 360-364.

Chakraborty, S., Kanhaisingh, A., Greenfield, P.F., Reid, S., Monsour, C.J. & Teakle, R.E. (1995) In vitro production of wild type heliothis baculoviruses for use as biopesticides. Australas. Biotechnol. 5: 82-86.

Desgranges, C., Vergoignan, C., Lereec, A., Riba, G. & Durand, A. (1993) Use of solid state fermentation to produce Beauveria bassiana for the biological control of European corn borer. Biotech. Adv. 11: 577-587.

Feng, M.G., Poprawski, T.J. & Khachatourians, G.G. (1994) Production, formulation and application of the entomopathogenic fungus Beauveria bassiana for insect control: Current status. Biocontrol Sci. Tech. 4: 3-34.

Foster, J., Brough, E. & Norton, G. (1994) Integrated pest management in Australia: making it happen. Agric. Sci. 7(5): 39-42.

Lane, B.S., Trinci, A.P.J. & Gillespie, A.T. (1991) Influence of cultural conditions on the virulence of conidia and blastospores of Beauveria bassiana to the green leafhopper, Nephotettix virescens. Mycol. Res. 95: 829-833.

Lisansky, S.G. (1995) The potential for biopesticides. L-N "Proceedings of the 1st Brisbane Symposium, Biopesticides: Opportunities for Australian Industry" edited by C.J. Monsour, S. Reid & R.E. Teakle (Dept. of Chemical Engineering, University of Queensland) pages 1-7.

Lomer, C.J., & Prior, C. (Eds) (1991) Biological Control of Locusts and Grasshoppers. (Proceedings of a workshop held at the International Institute of Tropical Agriculture, Cotonou, Republic of Benin, 26 April-1 May 1991). (CAB International, Oxford) 394 pages.

Pitt, I. (1995) Environmental considerations in the regulation of naturally occurring and genetically modified biopesticides. IN "Proceedings of the 1st Brisbane Symposium, Biopesticides: Opportunities for Australian Industry" edited by C.J. Monsour, S. Reid & R.E. Teakle (Dept. of Chemical Engineering, University of Queensland) pages 118-121.

Stafford, C.J. (1995) Production and Formulation of Bt. IN "Proceedings of the 1st Brisbane Symposium, Biopesticides: Opportunities for Australian Industry" edited by C.J. Monsour, S. Reid & R.E. Teakle (Dept. of Chemical Engineering, University of Queensland) pages 78-83.

Taverner, E. (1995) Registration requirements for new biopesticides in Australia. IN "Proceedings of the 1st Brisbane Symposium, Biopesticides: Opportunities for Australian Industry" edited by C.J. Monsour, S. Reid & R.E. Teakle (Dept. of Chemical Engineering, University of Queensland) pages 115-117.

Whitten, M.J. (1995) Foreword. IN "Proceedings of the 1st Brisbane Symposium, Biopesticides: Opportunities for Australian Industry" edited by C.J. Monsour, S. Reid & R.E. Teakle (Dept. of Chemical Engineering, University of Queensland) pages v-vi.

Copyright 1996 Australian Biotechnology Association Ltd.