Impacts on Insect and Mite Pests - Climate Resilient Agriculture for Ensuring Food Security - page 118

potato beetle - possibly resulting in more genera-
tions (and crop damage) per year.
Lower winter mortality of insects due to
warmer winter temperatures could be important
in increasing insect populations (Harrington et al.
2001 ). Higher average temperature might result
in some crops being able to be grown in regions
further north - it is likely that at least some of the
insect pests of those crops will follow the
expanded crop areas. Insect species diversity per
area tends to decrease with higher latitude and
altitude (Andrew and Hughes 2005 ), meaning
that rising temperatures could result in more
insect species attacking more hosts in temperate
climates (Bale et al. 2002 ). Bale et al. ( 2002 ) con-
cluded that the diversity of insect species and the
intensity of their feeding have increased histori-
cally with increasing temperature.
Positive physiological responses to increasing
temperatures will allow for faster insect growth
and movement. Additionally, milder winters will
allow for earlier insect growth and a reduction in
overwinter deaths. The expansion or shift in
ranges coupled with an increase in growth and
numbers will likely result in an increase in insect
invasions.
Global warming will lead to earlier infestation
by Heliothis zea in North America (EPA 1989 )
and Helicoverpa armigera in North India
(Sharma et al. 2010 ), resulting in increased crop
loss. Rising temperatures are likely to result in
availability of new niches for insect pests.
An increase of 3 °C in mean daily temperature
would cause the carrot fl y, Delia radicum , to
become active a month earlier than at present
(Collier et al. 1991 ), and temperature increases of
5-10 °C would result in completion of four gen-
erations each year, necessitating adoption of new
pest control strategies.
As stated earlier the temperature being the
single most important regulating factor for insects
(Yamamura and Kiritani 1998 ; Bale et al. 2002 ;
Petzoldt and Seaman 2010 ), global increase in
temperature within certain favorable range may
accelerate the rates of development, reproduc-
tion, and survival in tropical and subtropical
insects. Consequently, insects will be capable of
completing more number of generations per year,

and ultimately, it will result in more crop damage
(Yamamura and Kiritani 1998 ; Petzoldt and
Seaman 2010 ).
The impacts of climate change on seasonabil-
ity of insects have been studied by many workers
(Bale et al. 2002 ). The studies showed that
declined survival rate of brown planthopper,
Nilaparvata lugens , and rice leaf folder,
Cnaphalocrocis medinalis , at higher temperature
indicates the impacts of rising temperature could
do the changes in the pest population dynamics
of rice ecosystem.
Changes in temperature may have highly non-
linear effects on tritrophic interactions of host,
pathogen, and biocontrol agent. In wheat (152), a
rise in temperature from 17 to 22 °C resulted in
an increase in aphid ( Sitobion avenae ) reproduc-
tion by 10 %; at the same time, however, preda-
tory activity by lady beetle ( Coccinella
septempunctata ) adults increased by 250 %.
Aphid damage was reduced further because of
earlier maturity of the crop.
Climate change resulting in increased temper-
ature could impact crop-pest insect populations
in several complex ways. Although some climate
change temperature effects might tend to depress
insect populations, most researchers seem to
agree that warmer temperatures in temperate cli-
mates will result in more types and higher popu-
lations of insects.
Researchers have shown that increased tem-
peratures can potentially affect insect survival,
development, geographic range, and population
size. Temperature can impact insect physiology
and development directly or indirectly through
the physiology or existence of hosts. Depending
on the development “strategy” of an insect spe-
cies, temperature can exert different effects (Bale
et al. 2002 ). Some insects take several years to
complete one life cycle - these insects (cicadas,
arctic moths) will tend to moderate temperature
variability over the course of their life history.
Some crop-pests are “stop and go” developers in
relation to temperature - they develop more
rapidly during periods of time with suitable tem-
peratures. We often use degree-day or phenol-
ogy-based models to predict the emergence of
these insects and their potential to damage crops