Integrated pest management involves the integrated use of four
basic control techniques.
- 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.
- 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.
- 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.
- 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.
