|Keywords:||Biopesticides; Disease/pest resistance.|
|Correct citation:||Waage, J. (1997), "What Does Biotechnology Bring to Integrated Pest Management?" Biotechnology and Development Monitor, No. 32, p. 1921.|
Integrated Pest Management (IPM) is today a widely accepted strategy to reduce overdependence on chemical insecticides and their potentially negative environmental and economic effects. Biotechnology has considerable potential to contribute to sustainable biological elements of IPM. However, biotechnology development to date has been directed at more conventional models for pest control technologies.
Biotechnology for insect pest management has to some extent been an early byproduct of the acquisition of biotechnological knowhow, which will have more substantial implications for agriculture than simply improved IPM. In this context, the relative lack of strategic planning of biotechnology for IPM can be better understood. However, biotechnology has now entered pest management with much fanfare and expectations. It has enormous potential to improve pest management, but also to distort pest management, if it is seen as a set of singletechnology solutions which can replace a more diversified, sustainable and farmerparticipatory approach to IPM.
Trends in IPM
IPM has arisen from a need to reduce dependence on chemical insecticides, whose misuse in many crop systems has led to negative effects on environment and health, and to pest resistance and resurgence. Pest resurgence is an increase in pest numbers following pesticide use, which usually results from elimination by pesticides of important predators, parasites and other natural enemies of the pest. "Insecticide treadmills", characterized by rising pesticide use, growing pest problems and ultimately a decline in production and the viability of the farming system have appeared repeatedly around the world in heavilysprayed crops such as cotton, rice, fruit trees and vegetables. Solving these problems through IPM has usually involved dramatic reduction in insecticide use and its replacement by a range of control methods. These include cultural methods, plant resistance to pests, conservation of natural enemies in the crop and the use of pest control products which are safe to natural enemies, including biological pesticides and attractant traps for pests.
The recent history of rice production in Asia provides an example of the development of IPM. In the 1970s, Indonesia embarked on a rice intensification scheme based on new, highyielding Green Revolution varieties supported by fertilizer and insecticide inputs. Production increased, but with it emerged a new insect pest, the brown planthopper, Nilaparvata lugens. This was a result of the elimination of local natural enemies by insecticides. As damage spread across hundreds of thousands of hectares, new rice varieties bearing planthopper resistance were introduced in 1980. Production was restored, but only for four years. A high level of pest pressure on crops continued because pesticide use increased pest numbers. This accelerated selection for resistance in the pest population, and plant resistance broke down. Production was finally restored after the government prohibited the use of most insecticides on rice and implemented a programme of farmer training which focused on three principles: grow a healthy crop, inspect fields regularly and conserve natural enemies. In these training programmes, called "farmer field schools", farmers 'learn by doing' about pests, natural enemies and pest control measures in their own crops. IPM programmes of this kind have now trained over a million farmers in rice and other crops in Asia. Participatory IPM involves farmers in actively building and selecting the elements of their own local IPM systems. Today, IPM systems are adapted to suit various farming systems ranging from highinput to organic farming, whereby chemical use is either minimized or completely omitted. The global importance of this approach is highlighted in Agenda 21, which calls on all countries to implement farmerparticipatory IPM by the end of the century.
This example illustrates the importance of natural biological control in IPM. Interventions with products, like chemical pesticides and even resistant plant varieties, failed to control the pest because, in the absence of other natural controlling factors, the pest could quickly develop resistance to these singletechnology solutions. The success of biotechnology in IPM will depend on how it is used. While it provides the tools to modify performance of the important biological elements of pest control, like natural enemies and plant varieties, if it is used to produce pesticidelike, singletechnology solutions, its value and sustainability may be limited.
What has biotechnology brought to IPM
In order to understand whether biotechnology is making a positive contribution to IPM, it is useful to review the pest control biotechnologies presently available or in development. One focus of biotechnological research has been on improving natural enemies of pests as pest control agents. This has focused principally on pathogens of insect pests and their use as formulated biological pesticides. Emphasis has been placed on bacteria and viruses, largely because they are better understood and more easily manipulated, as opposed to fungi, protozoa, nematodes and arthropod predators.
Research on bacteria has concentrated on Bacillus thuringiensis (Bt), which is already widely used as a biopesticidal formulation to control caterpillar and beetle pests of crops, and flies which are disease vectors. Research has focused on increasing the host range and virulence of Bt by combining genes with different host specificities and properties. Research is also underway on improvement of Xenorhabdus spp., the bacteria responsible for the mortality of nematodeinfected hosts. Here the emphasis is on stabilizing and improving the virulence of these bacteria.
Insect viruses also have a market in their natural form as biopesticides, mostly against caterpillar pests of forestry and field crops. Biotechnological research has focused on engineering of certain viruses to express genes whose toxins kill faster than the wildtype viruses.
The second principle area of biotechnology for pest control has been the development of crop varieties resistant to pests and diseases. This has concentrated on incorporating insect and virus resistance into the plant genome. In addition, modification of the genome of plantassociated microorganisms has been followed as a strategy to confer insect resistance to plants. By far the most extensive application has been the incorporation of genes which produce various Bt delta endotoxins into crops, primarily to confer resistance against caterpillars and beetle pests.
In 1996, the first commercial transgenic varieties of cotton, maize and potatoes were released in the USA. Research is also conducted on incorporating genes for plant or microbiallyderived compounds which affect insect pests, such as trypsin inhibitase and cholesterol oxidase.
Overall, the application of biotechnology to IPM has so far been quite conservative. It has focused largely on improvement of existing crop protection products or technologies by use and manipulation of viral and bacterial genomes. Thus, engineered viruses and bacteria are variants of existing biopesticidal formulations of the same species. Some transgenic plants or plantassociated bacteria seek to improve on what can already be achieved less effectively by topical application of particular microorganisms, particularly Bt.
The technical objectives of many of these manipulations are directed at improving the performance of an engineered product relative to its "wildtype" competitor by:
The rationale has much to do with competition with existing products and the rapid acquisition of large markets. To consider how they may succeed at this, it is useful to examine the future of the relevant areas of pest control, namely biopesticides and host plant resistance.
Biotechnology in biopesticide development
Today there are over a hundred commercial biological control products on the market, and many more are locally produced and supplied for particular productions systems. However, most commercial biological control have focused on insect pathogens, because of their relative ease of mass production and their capacity to be used in the same manner as formulated chemical insecticides.
Bt has been the principle target of product development, and accounts for most sales in the US$ 75 million global market for biological control products. However, this is only less than one per cent of global pesticide sales.
As a product, Bt is valuable in IPM systems because it is much less harmful to predators and parasites than broad spectrum chemical insecticides. Therefore, it can be substituted for chemical products in "insecticide treadmill" situations and will allow the recovery of natural enemy populations. Like many biopesticides, it is often less effective on its own than a highly potent chemical product. However in an IPM system, where it is used only when needed and it conserves natural enemies, its impact is augmented by the action of those natural enemies (which is freeofcharge to the farmer) and it can be both more economical and sustainable. However, present product registration and evaluation systems often neglect this, favouring through various procedures and protocols the development of "this is all you need" products.
A second problem facing Bt is the risk of resistance. Where Bt is still used as a singletechnology solution, like its chemical predecessors, it is sprayed regularly and a range of insect pests are now developing resistance. Bt's third problem is that it lacks the most desirable biological property of a biological control agent: its ability to reproduce and perpetuate itself in crops. A key advantage of biological agents relative to chemical pesticides is their capacity to both kill pests (functional response) and reproduce at the expense of pest (numerical response) thereby giving some control in the future pest generations. Bt is not adapted to persist in the crop environment and its commercial development has focused less on preserving its ability to reproduce and spread, but more on maximizing the effect of its insectkilling toxin. In other words, its commercial development has focused on using it like a chemical insecticide and not as a living biological control agent. This is true of most biopesticide development today, such as that for nematodes and viruses. It also reflects the fact that the multinational agrochemical industries which have dominated biopesticide development have traditional skills and interests which are limited to the production and marketing of pesticidelike products.
Other insect pathogens are better adapted to having a continuous impact on pests in crops, such as viruses, fungi and protozoa, which can cause continuing outbreaks (epizootics) which suppress pests under natural conditions. However, these organisms are as yet little developed as biopesticides. Where biotechnology has been used in this process, the effect has been to reduce this desirable property of these biological control agents. For insect viruses, genes have been added or removed which cause the infected pest to die quickly. This means that the pest will die before the virus has replicated extensively, and fewer infective bodies may be released in the environment. Here, they may be less persistent due to their manipulation. There is even an incentive to ensure this because the environmental persistence of engineered organisms is not encouraged. In short, biotechnology has been used to turn living, reproducing viruses into quick kill products resembling the chemical pesticides with which they are expected to compete.
Biotechnology and crop resistance
Engineering genes for Bt toxins into plants is an ingenious method of delivering these toxins to pests which might naturally avoid them, such as insects which feed inside plants. From an IPM perspective, this technology has more similarities to plant resistance breeding than biopesticide development. Breeding for plant resistance to insect pests has a long tradition in the public and private sector, but its potential is far from realized. This is in part due to the popularity of other insect pest control methods, including insecticides and even IPM.
Most resistance breeding to date has focused on methods that result in vertical resistance wherein resistance is based on a single gene. It has geneforgene relationship whereby each gene of resistance in the host has a matching gene of parasitic ability in the parasite. Qualitatively, the resistance is either present or absent. This is contrary to horizontal resistance breeding, whereby resistance is based on many genes. Quantitatively, horizontal resistance is exhibited in varying degrees, from minimum to maximum.
Vertical resistance is convenient because high levels of resistance can be achieved and the method is compatible with breeding schemes used for enhancing crop performance through control of major genes. However, its geneforgene nature, can sometimes lead to its breakdown through the evolution of resistancebreaking pest genotypes, as in the case of brown planthopper on rice.
In an IPM context, the singletechnology solution promised by a high level of vertical resistance is not necessarily desirable if this brings the risk of resistance by the pest. The action of other IPM components like natural enemies can reduce pest populations and hence the rate of evolution of pest resistance. This means that partial resistance, or other forms of resistance like horizontal resistance which is built on the quantitative effect of many genes, can be effective and sustainable. Unfortunately, the tradition of plant breeding and now biotechnology for resistance to pests favours vertical resistance, with its inherent risks.
Suggested solutions to resistance problems involve more complex strategies of gene deployment. This includes mixed or intercropped populations of resistant and susceptible plants, or genetic methods to restrict expression of genes to certain parts of plant or certain times. Resistance management is therefore a strong possibility, but the track record of chemical pesticides is not encouraging.
Biotechnology for plant protection is still in its early days. So far, it has been focused conservatively on improving conventional pest control approaches, biological pesticides and vertical resistance in crops to pests, in order to make better, singletechnology solutions to insect pest problems, which will outcompete current, nonengineered products. Recent developments in IPM challenge these conventional approaches and products, and this in turn challenges the current direction of biotechnology in pest management. IPM promotes a more diversified approach which will limit overreliance on any specific technology and the consequences of this, such as resistance development. It promotes greater reliance on exploiting living, selfrenewing processes in pest control, such as the action of natural enemies of pests.
The future of biotechnology has much promise. Biological control and host plant resistance stand out as elements of IPM which are potentially selfrenewing and available to all farmers, rich or poor. Biotechnological innovations which improve the persistence or efficiency of these biological processes, for instance by improving survival or transmission rates of pathogens, or facilitating broadlybased quantitative crop resistance to pests, will be valuable to the sustainable IPM of the future. Beyond these areas, biotechnology has considerable potential application in improving mass production technologies for natural enemies of pests, and for improving diagnostic systems which allow scientists to recognize desirable plant genes and natural enemies, and which allow farmers to recognize potential pest problems before they cause damage. In its next generation, and with the benefit of the IPM experience, biotechnology stands to contribute greatly to sustainable pest management.
Director, International Institute of Biological Control, Buckhurst
Road, Ascot, Berks SL5 7TA UK.
Fax (+44) 1344 87 5007; Email email@example.com
J.K. Waage (1996), "Integrated Pest Management and Biotechnology: An analysis of their potential for integration". In: G.J. Persley, (ed.). Biotechnology and Integrated Pest Management. Oxon, UK: CAB International. pp. 3660.
J.K. Waage (1997), "Biopesticides at the Crossroads: IPM products or chemical clones?" In: Microbial Insecticides: Novelty or necessity? BCPC Proceedings No. 68. Proceedings for a Symposium, Warwick, UK, 1618 April 1996. Bracknell: BCPC Publications, pp. 1119.
M.B. Thomas and J.K. Waage (1996), Integrating Biological Control and Host Plant Resistance Breeding: A scientific and literature review. Wageningen: Technical Centre for Agricultural and Rural Cooperation of the European Union (CTA), 99p.
|back to top||