Impacts on Insect and Mite Pests - Climate Resilient Agriculture for Ensuring Food Security - page 114

coarse cereals, and wheat) (Dhaliwal et al. 2010 ).
Pest damage varies considerably in different
agroclimatic regions across the country mainly
due to differential impacts of several abiotic fac-
tors such as temperature, humidity, and rainfall
(Reed and Pawar 1982 ; Sharma et al. 2010 ). This
has major implication for the intensifi cation of
yield losses due to potential changes in crop
diversity and increased incidence of insect pests
in the context of impending climate change.

7.1 Crop Losses

Insect pests in agricultural systems are the major
cause of damage to yield quantity. The most
recent and comprehensive efforts to provide a
measure of global crop losses by insects are
those made by Oerke ( 2006 ) (Table 7.1 ). The
estimate of preharvest loss caused by animal
pests to the principal food and cash crops is 18 %
of potential production on a global basis (Oerke
2006 ). This high loss to pests is not uniform over
space and time, being proportionally higher in
Africa and under climate conditions favorable to
pests.
Agricultural trends are infl uencing the inci-
dence and importance of pests. First, the expan-
sion of worldwide trade in food and plant
products is spreading the impact of insects.
Second, changes in cultural techniques, particu-
larly intensifi cation of cropping, reduction in
crop rotations, and increase in monocultures,
encourage the activity of insect pests.
In North America, the average losses to insects
estimated for 1988-1990 are 13 % of the poten-
tial crop value. Among pesticides used for the
management of pests, insecticides account for
22 % (US$ 9 billion in 1997) (USDA 1999 ).
In India, the average annual losses have been
estimated to be 17.5 % valued at US$ 17.28 bil-
lion in nine major fi eld crops (cotton, rice, maize,
sugarcane, rapeseed-mustard, groundnut, pulses,

7.2 Climate Change

and Insect Pests

Losses due to insect damage are likely to increase
as a result of changes in crop diversity and
increased incidence of insect pests due to global
warming. Current estimates of changes in climate
indicate an increase in global mean annual tem-
peratures of 1 °C by 2025 and 3 °C by the end of
the next century. The date at which an equivalent
doubling of CO 2 will be attained is estimated to
be between 2025 and 2070, depending on the
level of emission of greenhouse gases (IPCC
1990a , b ). Mean annual temperature changes
between 3 and 6 °C are estimated to occur across
Europe, with greatest increases occurring at high
latitudes.
Pest menace under the infl uence of climatic
factors, at various stages of crop growth, is one of
the factors limiting agricultural productivity
(Oerke et al. 1994 ). Climate is an important
determinant of abundance and distribution of
species. The rising concentrations of CO 2 will
have a variety of direct effects on plants and may
also have indirect effects on herbivores and their
natural enemies. The climate has profound effects
on the populations of invertebrate pests like
insects, mites, and others and affects their devel-
opment, reproduction, and dispersal systems.
Extreme weather events such as intense rain-
storms, high wind, or elevated temperatures also
affect their survival. The climate change impacts
on pests may include shifts in species distribu-
tions with species shifting their ranges to higher
latitudes and elevations, changes in phenology

Table 7.1 Estimated potential of animal pests (arthro-
pods, nematodes, rodents, birds, snails, and slugs) and
actual losses due to pests in six major crops worldwide, in
2001-2003 (Oerke 2006 )

Crop losses (%) due to
animal pests
Potential

Attainable
production
(million tons) Crop Actual

Wheat 785.0 8.7 (7-10) 7.9 (5-10)

Rice 933.1 24.7 (13-26) 15.1 (7-18)

Maize 890.8 15.9 (12-19) 9.6 (6-19)

Potatoes 517.7 15.3 (14-20) 10.9 (7-13)

Soybeans 244.8 10.7 (4-16) 8.8 (3-16)

Cotton 78.5 a 36.8 (35-41) 12.3 (5-22)

a Seed cotton