Agriculture Reference
In-Depth Information
insecticide's mode of action. The surviving indi-
viduals possess a genetic mutation and then re-
produce. The proportion of individuals with the
mutation is greater in the subsequent generation.
Typically, resistance is noticed as a rate
response, where it takes a higher and higher
concentration of the pesticide to cause the same
percentage mortality. Nearly complete resistance
can result. Species that are multivoltine, or have
multiple generations per crop season, are more
likely to develop resistance. Colorado potato bee-
tle has developed resistance to several different
pesticides in most regions. Insecticides with a
single-site mode of action are most likely to de-
velop resistance. Resistance has been shown to
pyrethroid-type insecticides in many different
insect taxa. For multivoltine pests, it is very im-
portant to rotate or alternate pesticides with
different modes of action in order to reduce the
risk of insect populations developing resistance
to commonly used pesticides. In some regions,
insecticide cost and availability have a large im-
pact on the phenomenon of pesticide resistance.
Newer insecticides tend to have shorter
environmental persistence and are narrower in
spectrum of control; that is, they are usually
toxic to one or a few types of insects. Such prod-
ucts tend to be safer to the environment and
non-target insects, but are not immune to insects
developing resistance to them. Additionally, the
use of broad-spectrum insecticides has detri-
mental effects on insect natural enemies and can
cause flares of secondary pests, or pests typically
not associated with economic crop damage. An
example of this situation is the use of pyrethroid
insecticides to control midseason pests in the
western USA. Repeated use of pyrethroids can
cause late-season flares of two-spotted spider mites,
Tetranychus urticae
. This likely occurs because
the broad-spectrum pyrethroids are toxic to preda-
tory mites and insects that typically keep two-
spotted spider mite populations in check, but
those pyrethroids are not particularly toxic to
two-spotted spider mites.
We have given starting points on important
insects and sampling and management approaches,
but nothing substitutes for experience in the
field watching crop growth and insect activity.
As mentioned above, pest identification is
crucial to IPM, especially since many of the in-
sects found in potato fields may be natural en-
emies to pest insects. Conservation of beneficial
insects will reduce the likelihood of having to
apply insecticides for pests. Potato fields minim-
ally treated with pesticides can harbor a complex
food web of insects, spiders, and other arthro-
pods. These include a diverse set of decomposers
on and in the soil, predators and parasitoids in
and on the soil and on the foliage, and major and
minor pests such as those discussed above.
A major goal of some potato entomology
research has been to understand how best to man-
age the crop to maximize the use of this biodiversity
and limit pest damage. During the 1990s, transgenic
potatoes, containing the gene from
Bacillus thur-
ingiensis
that kills Colorado potato beetle, were
developed and briefly commercialized. This in-
novation allowed detailed study of the arthropod
community in a potato agroecosystem with little
to no insecticides (Reed
et al
., 2001), and showed
that eliminating the primary defoliating pest
without insecticides preserved a wide range of
beneficial generalist predators to control second-
ary pests. Koss
et al
. (2005) compared the arthro-
pod community in commercial fields under three
management regimes: broad-spectrum insecti-
cides, selective insecticides, and certified organic
management. They showed the use of selective
insecticides resulted in similar levels of predators as
in organic management, but with fewer pests.
Beneficial insects will be present in potato
fields in almost all production regions. Growers
and field staff should learn to recognize the main
predators and parasites of the pests in their re-
gions. This allows a fine-tuning of decisions to use
insecticides. For example, knowledge of a large
predator population in a field infested with pests
may encourage a grower to wait before applying
an insecticide, and thereby potentially realize all
needed control without the insecticide.
A combination of the general principles of
potato insect management and direct observa-
tions of local agroecosystems will give crop
managers most of the knowledge necessary to
minimize crop damage successfully and main-
tain profitability.
9.6 Summary
Throughout most of the world, potato crops are
attacked by several serious pest insects. Regardless
of a practitioner's location, it is critical to become
familiar with the pest insects in his or her area.
