Integrated pest management – the good, the bad and the genetically modified

Key text

In part, the development of integrated pest management (IPM) is a response to the failure of many chemical pesticides to provide long-term solutions to pest problems. While some pesticides have dramatic effects when first applied, many pests develop resistance to the chemical over time and often re-emerge to plague an industry. It can become a vicious circle – the farmer increases the rate of pesticide application, producing increasingly resistant 'super-bugs'. Large quantities of the poisons enter the soils and waterways of the region, with sometimes unforeseen and devastating effects on the environment and human health.

Pest resistance in the Ord

When large plantations of cotton were established in Western Australia's Ord River valley in the 1960s, the caterpillars (larvae) of two species of heliothis moth moved in. These destructive pests were controlled initially by pesticides, but, pretty soon, they started developing resistance. Farmers kept increasing the dosage, but they were fighting a losing battle. Eventually, as landholders went broke, switched to other crops or simply abandoned their properties, the industry collapsed.

Now, 25 years later, researchers are trialling an integrated pest management strategy to see if commercial cotton can again be grown in the Ord River valley. Many elements of the strategy were first developed in the Namoi Valley in New South Wales, another cotton-growing area. The strategy includes:

• Vastly improved understanding of the ecology and biology of pests and the crop itself.

• Monitoring the increase in insect pest numbers. This, combined with an understanding of their life cycles, allows pesticide spraying at the most effective times, reducing the need for large amounts of pesticide.

• Using different types of insecticides to reduce the likelihood of resistance to any one chemical building up.

• Increasing the numbers of natural predators. One of the side effects of high rates of pesticide use is that insects and other small animals that might otherwise feed on cotton pests are killed. As application rates decline, more of these beneficial animals survive and are able to play a more active role in suppressing insect pests.

• Cotton plant varieties that have been genetically engineered. They now include a gene taken from a bacterium (Bacillus thuringiensis, or Bt) that produces a protein which is toxic to heliothis caterpillars.

The key components of integrated pest management

Successful integrated pest management usually has several key components.

1. Knowledge. Understanding the biology and ecology of the pest, and the crop (or livestock) is essential. Information about interactions within agricultural ecosystems is also important. IPM draws on the fundamental knowledge of plant and insect biology accumulated by biologists.

2. Monitoring. Farmers can use relatively simple techniques to keep track of what pests are where. This information, combined with knowledge of pest life cycles, can enable farmers to implement control measures at the most effective times.

   For example, the pyrgo beetle is a major defoliating insect pest of tea tree in Australia. In the past, growers have used large quantities of chloropyrifos spray to control the beetle, but this chemical has been showing up as an undesirable residue in tea-tree oil products. Clearly, better ways are needed. Field trials have demonstrated that the placement of yellow sticky traps within tea-tree plantations gives growers an accurate picture of beetle distribution at an early stage of their life cycle, enabling better targeted control programs. These would reduce both the need for and the cost of applying chemical sprays.

   Monitoring on a broader scale can also be used to predict pest outbreaks and forewarn farmers to take action. For example, scientists at the Cooperative Research Centre for Tropical Pest Management have developed a computer model that can predict the migration of the heliothis moth using information on wind patterns and satellite data about the status of host plants and breeding sites.

3. Economic threshold. This takes into account the revenue losses resulting from pest damage and the costs of treatment to prevent the damage. Below the economic threshold, the presence of the pest is tolerated. Only when pest numbers increase above the threshold does the farmer take action.

4. Adaptability. Farmers must keep informed about what is happening in their paddocks so that they can adapt their strategies to changing circumstances. Research scientists, too, must aim to keep at least one step ahead of the pest, which is also undoubtedly changing and adapting over time.

Control techniques

A wide range of pest control techniques is available to farmers. Some of them are as old as agriculture itself – rotating a crop, for example, to avoid a build-up of host-specific pests. Some are new – in recent years, genetic engineering has opened up many possibilities in pest control that were unavailable to agriculturalists even a decade ago.

Integrating techniques

But farmers using integrated pest management don't hang their hats on any single technique. The simple philosophy is that control will be more effective, and resistance will be less likely to build up, when a range of measures is deployed against a pest (Box 2: Integrated pest management in the Australian apple industry). Wherever possible, different pest control techniques should work together rather than against each other. In some cases, this can lead to synergy – where the combined effect of different techniques is greater than would be expected from simply adding the individual effects together.

Fighting the good fight

Our knowledge of agricultural systems and their associated pests will continue to expand, enabling management efforts to become increasingly subtle, increasingly effective and increasingly benign to the environment.

Farmers should benefit too, from reduced handling of potentially toxic chemicals and from the increased satisfaction that comes with a heightened awareness of the farm ecosystem. They may feel less pain in the hip pocket, because the savings from the reduced use of pesticides will often outweigh the cost of integrated control measures. And the long-term sustainability of the farming systems may also be enhanced.

Pest control is a continuing struggle, because rarely are pests totally eradicated (and, in the case of native pests, this may not even be desirable). The ways are many, but the aim is the same: to find a balance, precarious though it may be, between the impact of the pest and the effort needed to suppress it.

Related Nova topics:

• A plague on the pest – rabbit calicivirus disease and biological control

Box 1. Pest control techniques

1. Physical controls

   Physical controls are those that can be carried out by the farmer to alter environmental factors in a way that reduces pest populations. A simple and common example of this is crop rotation, which is the practice of planting different crops each year in a given paddock. This interrupts the normal life cycle of some pests by changing their environment to one in which their favourite host plant does not feature. It is a strategy that has been used successfully for years by Australian gardeners against tomato nematodes.

   Another physical control method sometimes called 'mating disruption' involves the use of sex pheromones. These chemicals are produced by female insects to attract males for mating. For many insects, scientists have been able to analyse the chemistry of the sex pheromones and reproduce them synthetically in the lab. Quantities of the chemical placed around an orchard can disrupt mating – male insects become confused and are less likely to find a mate.

2. Biological control

   The principle behind biological pest control is that a given pest has enemies – predators, parasites or pathogens. By introducing or encouraging such enemies, the population of pest organisms should decline. It is not a new concept. The ancient Chinese encouraged ants in citrus orchards because they attacked many citrus pests.

   There are three general approaches to biological pest control. The first of these is importation of a biological agent. For example, the Mexican prickly pear once covered 250,000 square kilometres, mostly in Queensland, greatly reducing the land's carrying capacity for sheep and cattle. It was brought under control very effectively by the introduction of an Argentinian moth, Cactoblastis cactorum, the larvae of which eat the leaves of the offending plant.

   But there are dangers with this approach. When the cane toad (Bufo marinus) was introduced to north Queensland to reduce populations of the cane grub, Bufo failed to have any impact on the grub. Not only that, it has become a major pest itself, spreading through much of northern Australia and threatening the survival of several native animal species. Nowadays biologists are required to carry out extensive research before a control organism is released because it is important to find out whether it will attack species other than the pest species.

   The second approach to biological control is augmentation, which is the manipulation of existing natural enemies to increase their effectiveness. This can be achieved by mass production and periodic release of natural enemies of the pest, and by genetic enhancement of the enemies to increase their effectiveness at control.

   The third approach is conservation. This involves identifying and modifying factors that may limit the effectiveness of the natural enemy. In some situations, this may include reducing the application of pesticides, since such pesticides may kill predators at the same time as killing the pests (Box 2). Sometimes part of a crop area is left untreated so that natural enemies will survive and recolonise the treated areas.

3. Genetic modification

   Crop plants can be bred to be resistant to pests. Farmers and orchardists have been doing this for centuries, selecting the seeds of those plants least affected by a pest for use in the next year's crop. This preferential selection is a form of genetic modification.

   With advances in biotechnology and molecular biology, it is becoming increasingly easy to transfer resistance genes into a plant – this is called gene transformation or genetic engineering. An example of genetic engineering is the insecticide-producing Bt gene in cotton. Scientists took the gene from a bacterium and inserted it into a plant, making the plant resistant to insect attack. Similarly, potato plants have been genetically modified to increase their resistance to potato leaf roll virus.

   Another technique is the genetic modification of the pest itself. The idea is to engineer a disadvantageous trait in a pest and then release modified individuals into the outside world. The sterile insect release method is an example of this approach.

   The genetic engineering of organisms is controversial. Some people argue that toxins produced as a result of gene transfer may have harmful effects on beneficial organisms or on human health, while others suggest that the transferred gene might 'escape' into wild, related species of the modified organism, with possible ecological implications.

4. Chemical control

   The use of chemical pesticides often forms part of an integrated pest management strategy. The key is to use pesticides in a way that complements rather than hinders other elements in the strategy and which also limits negative environmental effects. It is important to understand the life cycle of a pest so that the pesticide can be applied when the pest is at its most vulnerable – the aim is to achieve maximum effect at minimum levels of pesticide.

Related sites

• Control of introduced species (Questacon, Australia)

• Australian Broadcasting Corporation
  • Some rice with that? (The Lab)
  • GM cotton (transcript of The Science Show, 18 May 2002)
  • Cotton (transcript of Ockham's Razor, 23 March 1997)
  • Our genetically engineered future – Bt cotton (transcript of Quantum, 15 August 1996)

• More food, cleaner food – gene technology and plants (Nova: Science in the news, Australian Academy of Science)

Box 2. Integrated pest management in the Australian apple industry

In the late 1940s, a new synthetic insecticide called dichloro-diphenyl-
trichloroethane (DDT) was used to control codling moth. Despite early success against the codling moth, it had some drawbacks. For a start, it led to an increase in the light-brown apple moth and the two-spotted mite, probably because it removed beneficial species that had previously kept these pests under control. Eventually, the codling moth also became resistant to DDT, so farmers switched to other insecticides. Scientists began looking for non-chemical alternatives, and a small number of farmers became interested in integrated pest management strategies.

But the turning point for the apple industry probably came in 1989, when research revealed that daminozide, a chemical used to regulate the shape and maturity of Red Delicious apples, was a potential carcinogen (cancer-causing agent). This rocked the industry, which almost immediately started developing a strategy to reduce the level of all chemicals used in apple production – including pesticides.

Towards integrated pest management in the apple industry

A key challenge has been to find a way of reducing codling moth populations without destroying beneficial insect predators at the same time. A biological control called the codling moth granulosis virus was investigated. Although successful in Europe, this virus has so far proved disappointing in Australia. Other techniques tested with varying degrees of success include mating disruption, biological control with a parasitic wasp, and more effective timing of pesticide applications due to improved monitoring.

With the reduced use of insecticides for the control of codling moth come other benefits. For example, the introduced predator of the two-spotted mite is able to survive, multiply and eventually reduce the population of the two-spotted mite.

More research on integrated pest management in the apple industry is currently underway. The situation is complicated by the fact that there is more than one significant pest. Researchers and farmers face the challenge of integrating techniques to ensure that attempts to control one pest don't prejudice attempts to control another.

Related site

• Cleaner and greener fruit (Museum Victoria)

Activities

• Global Education (AusAID, Australia)
  • Integrated pest management in Indonesia

• Biotechnology Online (Biotechnology Australia)
  • A problem with insects – students assess the extent of insect damage to Australian cotton crops, the most common ways of controlling insects in Australian cotton crops and the comparative costs of these methods.
  • Butterflies and Bt – students evaluate the possibility of Monarch butterflies being killed by pollen from genetically engineered plants.

• Queensland Department of Natural Resources and Mines, Australia
  • Pest animal educational resources – students learn about the dangers pest animals pose to native wildlife, domestic pets and farming communities.
  • Controlling pests – students learn the ways in which agricultural pests are controlled.
  • Weed educational resources – students learn to identify and manage weeds.

• Newton's Apple (USA)
  • Cockroaches

• Access Excellence (USA)
  • Pesticides and eggshell thinning

Further reading

Useful sites

Click on 'Environmental impacts of pest control and then 'IPM' to find out more about integrated pest management, using the cotton industry as an example.
http://www.adelaide.edu.au/agcareers/Content/content-framesets/TeacherResources.html

Integrated pest management (Quarantine, Pests and Diseases, Tasmanian Department of Primary Industries, Water and Environment, Australia)

Describes IPM by defining each of the component words integrated, pest and management. 'Tools in the toolbox' covers the range of management strategies that an IPM-aware farmer can use.
http://www.dpiwe.tas.gov.au/inter.nsf/WebPages/BHAN-52K479?open

An IPM primer (Northeastern IPM Center, USA)

Contains IPM definitions and a generalised IPM program.
http://northeastipm.org/whatisprimer.cfm

Integrated weed management manual (CRC for Australian Weed Management, Australia)

A manual for the prevention of herbicide resistance through integrated weed management
http://weedscrc.org.au/publications/iwm_manual_flyer.html

Integrated pest management (Garden Web, USA)

How you can apply integrated pest management in your garden.
http://www.au.gardenweb.com/sesbania/ipm.html

Glossary

genetic engineering. A set of procedures whereby a specific piece of DNA can be excised from a chromosome and inserted into the DNA of a chromosome of a different organism.

pathogen. An organism capable of causing a disease.

protein. A large molecule composed of a linear sequence of amino acids. This linear sequence is a protein's primary structure. Short sequences within the protein molecule can interact to form regular folds (eg, alpha helix and beta pleated sheet) called the secondary structure. Further folding from interaction between sites in the secondary structure forms the tertiary structure of the protein.

Proteins are essential to the structure and function of cells. They account for more than 50 per cent of the dry weight of most cells, and are involved in most cell processes. Examples of proteins include enzymes, collagen in tendons and ligaments and some hormones. More information can be found at Protein structure and diversity (Molecular Biology Notebook, Rothamsted Research, UK).

resistance (biological). The ability to withstand the effects of a disease-causing organism.