雅思阅读题目练习：Biological Pest Control_雅思
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A. Biological control is, generally, human’s use of a specially chosen
living organism to control a particular pest. This chosen organism might be a
predator, parasite, or disease which will attack the harmful insect. It is a
form of manipulating nature to increase a desired effect. A complete Biological
Control program may range from choosing a pesticide which will be least harmful
to beneficial insects, to raising and releasing one insect to have it attack
another, almost like a “living insecticide”.
B. Biological control methods can be used as part of an overall Integrated
Pest Management (IPM) program to reduce the legal, environmental, and public
safety hazards of chemicals. In addition, it may be a more economical
alternative to some insecticides. Some biological control measures can actually
prevent economic damage to agricultural crops. Unlike most insecticides,
biological controls are often very specific for a particular pest. Other helpful
insects, animals, or people can go completely unaffected or disturbed by their
use. There is less danger of impact on the environment and water quality.
C. Biological control takes more intensive management and planning. It can
take more time, require more record keeping, more patience, and sometimes more
education or training. Successful use of biological control requires a greater
understanding of the biology of both the pest and its enemies. Many natural
enemies are very susceptible to pesticides, and using them successfully in an
IPM program takes great care. In some cases, biological control may be more
costly than pesticides. Often, the results of using biological control are not
as dramatic or quick as the results of pesticide use. Most natural enemies
attack only specific types of insects —unlike broad-spectrum insecticides, which
may kill a wide range of insects. Though often an advantage, this can also be a
disadvantage.
D. Biological control uses naturally occurring predators, parasites and
diseases to control pests. There are three main ways to use these natural
enemies against unwanted insect pest populations. Classical Biological Control
(importation) involves traveling to the country or area from which a newly
introduced pest originated and returning with some of the natural enemies that
attacked it and kept it from being a pest there. New pests are constantly
arriving accidentally or intentionally. Sometimes they survive. When they come,
their enemies are left behind. If they become a pest, introducing some of their
natural enemies can be an important way to reduce the amount of harm they can
do. Augmentation is a method of increasing the population of a natural enemy
which attacks a pest. This can be done by mass producing a pest in a laboratory
and releasing it into the field at the proper time. Another method of
augmentation is breeding a better natural enemy which can attack or find its
prey more effectively. Mass rearings can be released at special times when the
pest is most susceptible and natural enemies are not yet present, or they can be
released in such large numbers that few pests go untouched by their enemies. The
augmentation method relies upon continual human management and does not provide
a permanent solution unlike the importation or conservation approaches may.
Conservation of natural enemies is an important part in any biological control
effort. This involves identifying any factors that limit the effectiveness of a
particular natural enemy and changing them to help the beneficial species.
Conservation of natural enemies involves either reducing factors which interfere
with the natural enemies or providing needed resources that help natural
enemies.
E. In addition to the introduction of predators, several microbial
pathogens are effective against nematodes. They consist of a microorganism (e.g.
a bacterium, fungus, virus or protozoan) as the active ingredient. They can
control many different kinds of pests, although each separate active ingredient
is relatively specific for its target pest (s). For example, there are fungi
that control certain weeds, and other fungi that kill specific insects. The most
widely used microbial pesticides are subspecies and strains of Bacillus
thuringiensis, or BT. Each strain of this bacterium produces a different mix of
proteins, and specifically kills one or a few related species of insect larvae.
While some BT’s control moth larvae found on plants, other BT’s are specific for
larvae of flies and mosquitoes. The target insect species are determined by
whether the particular BT produces a protein that can bind to a larval gut
receptor, thereby causing the insect larvae to starve.
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