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To most of us, insects are vermin, pests and a nuisance. This is attributed to poor dissemination of
information about insects. Many of us are aware of pests because we learn about them in school and are
bombarded with advertisements on the need to destroy vermin. Little attention is placed on telling the
public about fascinating insects that are our friends. It has been estimated that there are more friendly
insects than pestilent ones. Indeed, it is because of these friendly insects that we have been able to grow
food as most pest species are kept in check by them. You may already know about insects like bees that
produce honey, and silkworms that produce silk. There are also the insects that are allies of farmers.
In the Cameron Highlands, an important vegetable crop cultivated by farmers is the head cabbage.
Since the Highlands was opened for agriculture in the late 1930's, this temperate climate crop has been
widely grown. However, unknown to farmers then, an insect from the temperate lands had accompanied
the vegetable to Malaysia. This insect was the diamondback moth. The moth is a small dull-looking
insect, the female of which lays large numbers of eggs on leaves of cabbages. These hatch in about five
days into small green caterpillars. Feeding by large numbers, these caterpillars could destroy cabbage
plants.
Initially, farmers in Cameron Highlands relied on chemical insecticides to control the pest. However,
the insect soon developed a resistance to the insecticides. An ecological approach was adopted in 1970
and this resulted in the importation of several species of small parasitic wasps. These wasps will search
for the diamondback moth caterpillars. When these are found, the female wasps would inject an egg into
the body of the caterpillar. Soon a parasite would develop within the body of the caterpillar and eventually
kill it. A new wasp would develop from each parasitized caterpillar. This form of using parasitic insects to
control a pest is known as biological control.
Biological control is using 'nature to control nature'. When effectively established, biological control
often would not require further intervention by farmers. The parasitic wasps are truly friends of the
farmers. Farmers would save on expensive insecticides and apply them only when necessary, such as for
other pests. When carrying out biological control, only friendly insects that are very `host specific' are
used. This. means that there would be little or no risk of importing a pest. Often such an approach requires
an investment of time and money to allow biological control scientists carry out investigations in the place
of origin of the pest.
Besides using insects to control insects, scientists in Malaysia have also experimented with using
insects to control weeds. Weeds are unwanted plants. Often, these weeds come about because they were
introduced from another country. For example, there was interest in moving plants from the tropics of
South America to Malaysia in the last century. Arising from this is the introduction of rubber trees.
However, not all introductions were beneficial. One plant imported for hedge was found to grow very
well in coconut plantings, and almost everywhere. This was the string-bush. In some instances, the weed
competed with young coconut palms. Scientists at the International Institute of Biological Control found
that the weed was regulated in its native home of
Trinidad by a seed-feeding wasp and a leaf-feeding
beetle. Both were carefully studied and after exhaustive
testing, were imported and released into fields where
the weed was present. |
