Agriculture Reference
In-Depth Information
become susceptible to this pest under high
humidity and moderate temperatures near the
Equator in Kenya. There will be increased
impact on insect pests which benefi t from
reduced host defenses as a result of the stress
caused by the lack of adaptation to suboptimal
climatic conditions.
nitrogen-based defenses like alkaloids and in turn
may increase in carbon-based defenses such as
tannins (Roth and Lindroth 1995 ; Coviella and
Trumble 1999 ; Gutierrez et al. 2008 ). This
enhances the feeding by insect herbivores in
order to obtain suffi cient nitrogen for their
metabolism (Coviella and Trumble 1999 ).
Ultimately, it slows down insect development
and increases the length of life stages resulting in
more foliage feeding than normal (Coviella and
Trumble 1999 ).
In CO 2 -enriched atmosphere, water use effi -
ciency of plants increases owing to the reduced
water loss through less stomatal opening
(Groninger et al. 1996 ). Increased water content
in plants is benefi cial for most of the herbivorous
insects as it helps in nutrient assimilation and
digestion especially nitrogen (Reitz et al. 1997 ).
Increased water use effi ciency enables the plants
to extend their life spans providing longer peri-
ods of habitat suitability for transient insects. On
the contrary, under elevated temperature, the con-
centrations of certain allellochemicals like ter-
penes and phenolic compounds increase in plants
that act as defensives against the attacking insect
pests (Roth and Lindroth 1995 ; Coviella and
Trumble 1999 ; Gutierrez et al. 2008 ).
Temperature and photoperiod have been found
to affect profoundly the critical events such as
stem elongation, fl owering, and fruiting in the
life cycle of plants (Cleland et al. 2007 ). Global
warming that leads to increased temperatures
may accelerate the life cycles in some of the plant
species (Parmesan and Yohe 2003 ; Willis et al.
2008 ) which may affect, signifi cantly, feeding
and reproduction patterns in associated insect
pests like aphids, jassids, mealy bugs, etc. Such
increases can greatly exacerbate the negative
ecological
7.12
Pest Population Dynamics
and Outbreaks
Climate change resultant abiotic environment
(increased temperature, elevated CO 2 , and
depleted soil moisture) will affect signifi cantly
the diversity and abundance of insect pests
through geographic range expansion, increased
overwintering survival, and more number of gen-
erations per year, thereby increasing the extent of
crop losses. It may result in upsetting ecological
balance because of unpredictable changes in the
population of insect pests along with their exist-
ing and potential natural enemies.
Changes in climatic variables have led to
increased frequency and intensity of outbreaks of
insect pests. Outbreak of sugarcane woolly aphid,
Ceratovacuna lanigera , in sugarcane belt of
Karnataka and Maharashtra states during 2002-
2003 resulted in 30 % yield losses. These situa-
tions of increased and frequent pest damage to
the crops have made another big hole in the pock-
ets of already distressed farmers by increasing
the cost of plant protection and reducing the mar-
gin of profi t (Table 7.7 ).
7.13
Crop-Pest Interactions
The increasing temperature and CO 2 have been
found to exert both bottom-up and top-down
effects on the tritrophic interactions between
crops, insects, and natural enemies by means of
certain physiological changes especially related
to host suitability and nutritional status (Table 7.8 )
(Roth and Lindroth 1995 ; Coviella and Trumble
1999 ; Gutierrez et al. 2008 ). The CO 2 -enriched
environment reduces the nitrogen content of the
plant tissue due to widening of carbon-nitrogen
and
economical
consequences
(Timoney 2003 ).
7.14
Disruption of Plant-
Pollinator Interactions
Insects play a vital role in providing various ecosys-
tem services, a foundation for human life on earth
(Kannan and James 2009 ). One of the important
 
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