Pest management - Ecological Applications: Toward a Sustainable World - page 154

were applied to large areas of Illinois in the 1950s to 'eradicate' a grassland pest, the
Japanese beetle ( Popillia japonica ), cattle and sheep were poisoned, 90% of cats and
a number of dogs were killed, and 12 wild mammals and 19 bird species suffered
losses (Luckman & Decker, 1960).
Not surprisingly, given that pesticides kill a range of living organisms, many also
pose risks to human health. Indeed, repeated exposure to some pesticides can cause
cancer, birth defects, blood disorders, brain damage and kidney problems. And
because the nervous systems of insects and humans have much in common, even a
single dose of one of the nerve poisons (e.g. organophosphates or carbamates) can
lead to dizziness, twitching, seizures or death. For all these reasons, many old
pesticides are no longer used, while a very rigorous testing regime is applied to
new pesticides and instructions for their safe use are prominently displayed
on packaging.
If chemical pesticides brought nothing but problems, and if their use was intrinsi-
cally unsustainable, they would already have fallen out of widespread use. But
instead their rate of production has continued to increase rapidly because the ratio
of cost to benefi t for the individual user has generally remained in favor of pesticide
use. However, the many examples of undesirable outcomes argue for a precautionary
approach in any pest management exercise. Coupled with much improved knowl-
edge about toxicity and the development of more specifi c and less persistent pesti-
cides, such disasters should generally be a thing of the past. But note that in many
poorer countries, the prospect of imminent mass starvation, or of an epidemic
disease, are so frightening that the environmental and health costs of using pesti-
cides may sometimes have to be ignored.

6.3 Biological
control

Outbreaks of pests occur repeatedly and so does the need to apply pesticides. But
pest controllers can sometimes replace chemicals with another tool that can be more
effective and, over the long term, often costs a great deal less - biological control.
Biological control, or the manipulation of natural enemies of the pest, involves the
application of theory about interactions between species and their natural enemies
(Box 6.1) to limit the population density of specifi c pest species. There are three
main approaches.
The fi rst is the importation of a natural enemy from another geographical area -
often the area where the pest originated (Section 6.3.1). The objective is for the
control agent to persist and thus maintain the pest below its economic threshold for
the foreseeable future. This is a case of a desirable invasion of an exotic species and
is often called classical biological control .
By contrast, conservation biological control involves manipulations to increase the
equilibrium density of natural enemies that are already native to the region where
the pest occurs naturally or is an invader (Section 6.3.2).
Augmentation is similar to importation , but its aim is to temporarily supplement
an existing population without the expectation of a long-term increase in the enemy
population. Augmentation has to be carried out repeatedly, typically to head off
periods of rapid growth of the pest population, and provides control for one or a
few pest generations. Augmentation has two classes. Inoculation is where the released
natural enemies (fi eld-collected or laboratory-reared) serve to inoculate a new crop
but control is provided later by their offspring (Section 6.3.3). Inundation , on
the other hand, is where all control is provided by the released natural enemies