Agriculture Reference
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Fig. 7.5 Trap catch data indicating possible overwintering of corn earworm in western NY
have better advantage to survive great deal of
environmental adversities. There are two main
types of insect diapause: aestivation and hiberna-
tion to sustain life under high and low tempera-
ture extremes, respectively (Chapman 1998 ).
The studies have shown that global warming
is occurring notably in winter than in summer
and is greatest at high latitudes (IMD 2010 ).
Looking at the past 100 years' climate profi le of
India, warming was more pronounced during
winter season, and it was the minimum and not
the maximum temperature where signifi cant
increase was observed (IMD 2010 ). The tem-
perature in India is expected to increase by
1-5 °C within next 100 years (IMD 2010 ).
Thus, insects undergoing a winter diapause are
likely to experience the most signifi cant
changes in their thermal environment (Bale and
Hayward 2010 ).
Accelerated metabolic rates at higher tem-
peratures shorten the duration of insect diapause
due to faster depletion of stored nutrient
resources (Hahn and Denlinger 2007 ). Warming
in winter may cause delay in onset, and early
summer may lead to faster termination of dia-
pause in insects, which can then resume their
active growth and development. This gives an
important implication that increase in tempera-
ture in the range of 1-5 °C would increase insect
survival due to low winter mortality, increased
population buildup, early infestations, and
resultant crop damage by insect pests under
global warming scenario (Harrington et al.
2001 ; Sharma et al. 2010 ). Very few studies
have concentrated on the direct effects of higher
winter temperatures on rates of development
and reproduction in insects (Bale and Hayward
2010 ).
In New York, a network of pheromone traps
in sweet corn fi elds has been used to monitor
corn earworm ( Helicoverpa zea ) throughout
the central and western part of the state for
over 10 years. Corn earworm is thought not to
overwinter in upstate New York and is gener-
ally considered to be a late season, migratory
pest of sweet corn, so trapping was initiated in
mid-July. The graphs in Fig. 7.5 compare the
trap catches in 1995 with those in 2003 in Eden
Valley, NY.
During the early years of the trap network,
CEW traps remained empty until mid-late
August. After an unexpected early-season infes-
tation in Eden in 1999, trapping was initiated in
early June, and typically, low levels of moths are
caught through the early season, increasing
when the migratory fl ight arrives. It is yet to be
determined if the earlier arrival of corn earworm
indicates it is overwintering in Eden, but since
CEW management recommendations are based
on trap catches, it is clear that control of this pest
is already costing farmers more than it did
9 years ago.
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