Pest management - Ecological Applications: Toward a Sustainable World - page 168

Biological control
Biological control involves introducing or augmenting an enemy (predator, parasite
or pathogen). The control agent is often imported from the area where the pest
originated. When successful, the pest declines to a much lower equilibrium density,
and one that may be maintained because of the persistence, at low densities, of both
target and control agent. Biological control only needs to happen once, whereas
pesticides need to be used time and again. But as with pesticides, unwanted out-
comes of biological control occur when the control agent affects nontarget native
species. And if a biological control agent turns out to pose an environmental threat,
this may last forever.

Evolution of resistance
In fact, most pesticides have a limited life because pests evolve resistance to
them. Not all individuals in a genetically variable population will necessarily be
susceptible to the pesticide. These contribute more genes to future generations
and, if the pesticide is applied repeatedly, each successive generation of the pest
will contain a larger proportion of resistant individuals. Resistance does not usually
take long to appear and it can spread very rapidly in a population. In the face of
evolution of resistance, sustainable pest control depends either on the continual
development of new pesticides or management strategies that expose the pests to a
given pesticide for only a limited time. It has been extremely common for resistance
to pesticides to evolve, but it is also seen occasionally in response to biological
control agents.

Integrated pest management (IPM)
IPM considers how all the different tools at the pest controller's disposal can be
deployed most effectively to maximize economic benefi t and to minimize adverse
health and environmental consequences. IPM views crops and plantations as part
of functioning ecosystems, and management decisions take into account the effects
of control actions not only of pest but also other species in the web of community
interactions. IPM arose, in part, in reaction to the unthinking application of pesti-
cides in the 1940s and 1950s. The philosophy considers all possible control actions
(physical, cultural, chemical, biological and resistant crop varieties) before one is
adopted and, in most cases, integrates several control measures in a compatible
manner.

The fi nal word

Jenny would so love to eradicate the rabbits on her farm (Section 6.1). ' After I released
rabbit calicivirus disease, rabbit numbers certainly came crashing down, sheep produc-
tion improved and my annual poisoning costs disappeared. But now, a few years later,
the population seems to be on the rise. We are not using anything like the quantity of
poison we used to, but this year the helicopter will have to go up for a poison carrot drop
on some parts of the farm. '
Do you think that the reduction in potency of rabbit calicivirus disease (RCD) is
a result of evolution of resistance? How would you check this? The presence of RCD
in New Zealand has now prompted the government to legalize its use. Devise, in
outline, an IPM strategy for rabbit control that includes RCD. What other measures
would you include?