Pest management - Ecological Applications: Toward a Sustainable World - page 141

an early attempt to control rabbits - their descendants are now responsible for the
extinction or endangerment of many of New Zealand's native birds and unique
insects. Cat lovers abound, but predation by domestic and feral cats is a leading
cause of bird and lizard extinction around the world. Then there are the 'pet' plants
beloved by gardeners that escape into the wild and become pests, displacing native
species (Section 3.1).
So what exactly do we mean by the term 'pest'? The simple answer is a species
that (some) humans consider undesirable . This defi nition covers a multitude of sins.
Mosquitoes are pests because they carry diseases or because their bites itch; Allium
spp. are pest plants (weeds) because when harvested with wheat they make bread
taste of onions; rats and mice are pests because they feast on stored food; garden
weeds are pests for aesthetic reasons. Pests 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. People want rid of them all.
And where do pests come from? Many are exotic imports - such as rabbits, zebra
mussels and yellow star thistles (Section 1.2.5). Others are native but become an
economic problem when a new crop is introduced to a region. For example, when
European grasses appeared in New Zealand pasture, the native grass grub (larva of
the beetle Costelytra zealandica ) switched from native tussock grass to the new
pasture species and became a widespread pest. Other changes in agricultural prac-
tice have also turned native species into economic problems. The tendency to create
monocultures, something that went hand in hand with increased mechanization,
reduced habitat heterogeneity in a way that was deleterious to the natural enemies
of some crop-feeding herbivores, which increased to pest proportions as a result.
We will also see later how the application of pesticides can turn previously innocu-
ous species into pests.
Then there are species that my grandparents would not have considered pests,
but which my children certainly do. It used to be quite normal for people to eat
blemished apples, but our standards are now so exacting that the insects and fungi
responsible for blemishes have acquired pest status.
And fi nally there are pests that seem to arise from nowhere. For example, a sig-
nifi cant decline in rice productivity in Colombia was fi rst attributed to soil compac-
tion (so they increased ploughing), then to aphid damage and fi nally to nematode
infestation (prompting very high pesticide use) before the true cause was deter-
mined - a newly discovered virus (rice stripe necrosis virus). Such 'emerging infec-
tious diseases' seem to be a modern affl iction of plants in much the same way that
HIV and mad cow disease have affected human and animal populations (Anderson
et al., 2004).

6.1.2 Eradication or
control?

In Chapter 5 I considered how to apply population dynamics theory to the conserva-
tion of endangered species. The trick there was to work out what was necessary to
increase density and sustain the population into the future. My aim in this chapter
is to do the exact opposite - to drive a pest population extinct or keep density so
low that its nuisance value is negligible. Despite the diametrically opposed aims of
Chapters 5 and 6, they both rest on the same comprehensive knowledge of popula-
tion dynamics, genetics and evolution. The population concepts outlined in Boxes
5.1 and 5.2 are extended in Box 6.1 to underpin pest management. These boxes
should be considered together.