Pest management - Ecological Applications: Toward a Sustainable World - page 167

3 Biological control alone - involving the two currently most effective species, the
stem-mining moths Neurostrota gunniella and Carmenta mimosa , which can stunt
weed growth and reduce reproduction and recolonization.
4 Integrated weed management - 25 different single and combination treatments were
considered involving biocontrol, herbicide application, mechanical control and
fi re.
Of all the simulations, the most successful strategy was integrated weed management
involving biocontrol together with application of herbicide in year 1, mechanical
control and fi re in year 2, and herbicide again in year 3. This is indeed an integrated
pest management strategy.

Summary Pest eradication or control?

Pests are species that people consider undesirable. They carry an economic
cost, either because of direct damage to health or economic activity, or simply
because of a willingness to spend money to counter their nuisance value. Many
pests are exotic imports, but natives may achieve pest status after a change to agri-
cultural practices - by introducing new crops, creating monocultures or applying
pesticides.
The aim of pest control is to drive a pest population extinct or keep density
so low that its nuisance value is negligible. It can actually be very diffi cult to
eradicate a pest because most pests have very high reproductive rates. Eradication
may be attempted soon after an invader has arrived, when it is most vulnerable,
or where the consequences of the pest are particularly devastating - such as the
smallpox virus. More often, however, the aim is to reduce the pest population to a
level at which it does not pay to achieve yet more control (the 'economic injury
level').

Chemical control of pests
A very wide range of chemical pesticides has been developed. Some, known for
centuries, are naturally occurring defensive chemicals from plants (botanicals) -
although more effective forms are now synthesized in the laboratory. Other ancient
pesticides are the simple inorganics such as salts of copper and arsenic, but these
are little used today. Increasing knowledge of cellular physiology has seen the devel-
opment of much more sophisticated killers, including nerve poisons and disrupters
of natural cell function. The ideal pesticide would only affect the target species and
quickly break down in the environment. But there are many notorious cases of
pesticides that affect a wide range of species, persist for years, and pass along food
chains, accumulating in top predators.

Target pest resurgence and secondary pest outbreaks
Pest density may recover after pesticide application to densities far above the origi-
nal level. This 'target pest resurgence' occurs when treatment kills both large
numbers of the pest and large numbers of its natural enemies. Pest individuals that
survive the pesticide or that migrate into the area fi nd themselves with a plentiful
food resource and few, if any, natural enemies. And it may not only be the target
pest whose density surges. A number of innocuous herbivores, previously kept in
check by natural enemies, may achieve the status of 'secondary pest' because a pes-
ticide reduces numbers of their natural enemies.