140
READING PASSAGE 10
.
Biological control of pests
The continuous and reckless use of synthetic chemicals for the control of pests which pose a threat to
agricultural crops and human health
is proving to be counter-
productive. Apart from engendering widespread ecological disorders, pesticides have contributed to the
emergence of a new breed of chemical-resistant, highly lethal superbugs.
According to a recent study by the Food and Agriculture Organisation (FAO), more than 300 species of
agricultural pests have developed resistance to a wide range of potent chemicals. Not to be left behind are the
disease-spreading pests, about 100 species of which have become immune to a variety of insecticides now in
use.
One glaring disadvantage of pesticides’ application is that, while destroying harmful pests, they also wipe out
many useful non-targeted organisms, which keep the growth of the pest population in check. This results in
what agroecologists call the ‘treadmill syndrome’. Because of their tremendous breeding potential and
genetic diversity, many pests are known to withstand synthetic chemicals and bear offspring
with a built-in
resistance to pesticides.
The havoc that the ‘treadmill syndrome’ can bring about is well illustrated by what happened to cotton farmers
in Central America. In the early 1940s, basking in the glory of chemical-basedintensive agriculture, the
farmers avidly took to pesticides as a sure measure to boost crop yield. The insecticide was applied eight times
a year in the mid-1940s, rising to 28 in a season in the mid-1950s, following the sudden proliferation of three
new varieties of chemical-resistant pests.
By the mid-1960s, the situation took an alarming turn with the outbreak of four more new pests, necessitating
pesticide spraying to such an extent that 50% of the financial outlay on cotton production was accounted for
by pesticides. In the early 1970s, the spraying frequently reached 70 times a season as the farmers were pushed
to the wall by the invasion of genetically stronger insect species.
Most of the pesticides in the market today remain inadequately tested for properties that cause cancer and
mutations as well as for other adverse effects
on health, says a study by United States environmental agencies.
The United States National Resource Defense Council has found that DDT was the most popular of a long list
of dangerous chemicals in use.
In the face of the escalating perils from indiscriminate applications of pesticides, a more effective and
ecologically sound strategy of biological control, involving the selective use of natural enemies of the pest
population, is fast gaining popularity - though, as yet, it is a new field with limited potential. The advantage of
biological control in contrast to other methods is that it provides a relatively low-cost, perpetual control system
with a minimum of detrimental side-effects. When handled by experts,
bio-control is safe, non-polluting and
self-dispersing.
The Commonwealth Institute of Biological Control (CIBC) in Bangalore, with its
global network of research laboratories and field stations, is one of the most active, non-
commercial research agencies engaged in pest control by setting natural predators against parasites. CIBC also
serves as a clearing-house for the export and import of biological agents for pest control world-wide.
CIBC successfully used a seed-feeding weevil,
native to Mexico, to control the obnoxious parthenium weed,
known to exert devious influence on agriculture and human health in both India and Australia. Similarly the
Hyderabad-based Regional Research Laboratory (RRL), supported by CIBC, is now trying out an Argentinian
weevil for the eradication of water hyacinth, another dangerous weed, which has become a nuisance in many
parts of the world. According
to Mrs Kaiser Jamil of RRL, ‘The Argentinian weevil does not attack any other
141
plant and a pair of adult bugs could destroy the weed in 4-5 days.’ CIBC is also perfecting the technique for
breeding parasites that prey on ‘disapene scale’ insects - notorious defoliants of fruit trees in the US and India.
How effectively biological control can be pressed into service is proved by the following examples. In the late
1960s, when Sri Lanka’s flourishing coconut groves were plagued by leaf-mining hispides, a larval parasite
imported from Singapore brought the pest under control. A natural predator indigenous to India, Neodumetia
sangawani, was found useful in controlling the Rhodes grass-scale insect that was devouring
forage grass in
many parts of the US. By using Neochetina bruci, a beetle native to Brazil, scientists at Kerala Agricultural
University freed a 12-kilometre-long canal from the clutches of the weed Salvinia molesta, popularly called
‘African Payal’ in Kerala. About 30,000 hectares of rice fields in Kerala are infested by this weed.
