September 2014
40
FOCUS
Integratedpest control
Special
Managing insect pests in a changing
agro-ecosystemunder climate change scenarios
I
mpacts of global climate change can be
observed in many places, from rising
sea levels to melting snow and chang-
ing weather patterns, but the effects
on agro-ecosystems are one of the biggest
concerns as thiswill impact food security.
Maintaining food security is already be-
coming more of a challenge for smallhold-
er and commercial farms alike, but poorer
people are more vulnerable and will suffer
most from the negative impacts thereof.
Climate change causes highly variable con-
ditions including higher temperatures and
a shift of seasons as well as changes in
atmospheric gas composition (CO
2
levels),
changes in rainfall, variation in water avail-
abilityandextremenatural events. All these
changes will have a significant impact on
agriculture.
An important aspect to consider is the role
of insect pests within a changing environ-
ment in crop production systems. Insects
are strongly influenced by climate and
weather because they are cold-blooded.
Temperature, precipitation, humidity, wind
speed andother climatic parameters direct-
ly influence insect pests by affecting their
rate of development, reproduction, distri-
bution, migration and adaptation. Climate
will also affect the insects’ interactionswith
their host plant/s. Because most insects
have short generation times and are highly
adaptive, theywill be able to rapidly exploit
changing environmental conditions and im-
pact agro-ecosystems indifferent ways.
Increased temperatures
An increase in temperature may result in
the extension of the geographical range of
some insect pests.
The risk of invasion by migrant pests will
hereby be increased and in turn result in
pest insects causing damage to crops in
areas where they did not before. A shift
in seasonsmay result in a shorter overwin-
tering period, reduced overwintering mor-
tality and the extension of the development
season.
This will result in an increased number of
generations, consequently leading to in-
creased insect pressure on the emerging
ASTRID JANKIELSOHN,
ARC-Small Grain Institute
crops in the following season. Some pests
which are already present, but only occur
in small areas or at low densities, may be
able to exploit the changing conditions by
spreading more widely and reaching dam-
agingpopulationdensities.
Aphids, for instance, arekeypestsofagricul-
ture throughout theworld and are expected
to be particularly responsive to climate
change, because of their low developmen-
tal threshold temperature, short generation
time and considerabledispersal abilities.
Changes in temperature will also result in
changes in interspecific interactions and
crop-pestsynchrony.Differences inpatterns
of response to temperature change among
insect speciesmayaffect relationshipswith-
in foodwebs (host, pest andnatural enemy).
This could result in the emergence of new
pests or the new balance may even favour
thebuild-upof natural enemypopulations.
Pest insects may also be influenced by the
introduction of new alternative hosts and
“greenbridges” or overwinteringhosts as a
result of changing temperatures.
Increase inCO
2
levels
A change in the concentration of CO
2
levels
is likely to bring about changes in the qual-
ity of plant species, which may in turn af-
fect insect pests feeding on these plants.
Increased levels of atmospheric carbonwill
result in greater carbon:nitrogen-ratios in
plant foliage, which could stimulate increa-
sed feeding activity in some herbivores and
lead togreater cropdamage.
Changes in rainfall patterns
Rainfall pattern changes can have substan-
tial effects on insect populations. Droughts
makeplantsmorenutritious topests, as the
lack of water concentrates the amino acids.
Aphids can flourish during short droughts
as plant nutrients become more concen-
trated. Drought stressed plants also have
less resistance against feeding damage by
insects (
Photo1
). Predatorsandparasitesof
pests are furthermore affected by drought,
such as insect-killing fungi that require hu-
midity to germinate and are generally less
effectiveduringdroughts.
Extreme events
Extreme parameters can include tempera-
ture, precipitation, wind, light, humidity or
any unusual sequences of such extremes
or unusual combinations. Extreme events
have an impact on pest incidence in the
short term. Rapid changes in the climate
caused by extreme events can lead to
1: Drought stressedplants have less resistance against feedingdamageby insects.
