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Fig. 7.4
Drought infl uences on host plants, phytophagous insects, and their natural enemies leading to insect outbreaks
(Mattson and Haack
1987
)
corresponding decrease in the abundance of the
insects. Egg hatch and the termination of nymphal
hibernation occurred earlier in the winter-warmed
plots, but the rate of nymphal development was
unaffected.
survival at fi xed overwintering sites. Relationship
can then be established between winter mortality
and temperature.
Kiritani (
1971
) had examined the winter mor-
tality of adults of
Nezara viridula
in the late
March at fi xed overwintering sites from 1962 to
1967 in Wakayama. A regression between winter
mortality (
Y
) and the mean temperature in
January (
X
) [
Y
= -16.45
X
+ 147.08 (
R
2 = 0.6127,
P
< 0.0001)] suggested that every 1 °C rise around
X
= 4 °C would result in a decrease in winter mor-
tality by about 16.5 %.
Being poikilotherms, insects have limited
ability of homeostasis with external temperature
changes. Hence, they have developed a range of
strategies such as behavioral avoidance through
migration and physiological adaptations like dia-
pause to support life under thermally stressful
environments (Bale and Hayward
2010
).
Diapause is a period of suspended developmental
activities, the manifestation of which is governed
by environmental factors like temperature,
humidity, and photoperiod. As an adaptive trait,
diapause plays vital role in seasonal regulation of
insect life cycles because of which the insects
7.8
Drought
Drought stress sometimes brings increased insect
pest outbreaks. It is well known that drought can
change the physiology of host species, leading to
changes in the insects that feed on them (Mattson
and Haack
1987
) (Fig.
7.4
).
7.9
Increased Overwintering
Survival
Theoretically, it is hypothesized that the winter
survival of insects will be improved by an
increase in winter temperature, but the evidence
for this hypothesis is rather scarce. Effect of cli-
mate change on winter mortality/survival can be
examined by collecting long-term data on winter
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