Temperature-Based Phenology Modeling and GIS-Based Risk Mapping 421
relative humidity (RH) (Gautam 2008 ). About
2–3 gravid females of P. solenopsis were released
on the sprouted potato tubers kept in plastic jars
(10 cm diameter) with camel hair brush. The jars
were covered with clean black muslin cloth tied
with rubber band. The mealybug culture devel-
oped after 10–12 days was then used for subse-
quent studies.
Life Table Studies
The effects of temperature on development, sur-
vival, and reproduction of P. solenopsis were
studied on cohorts of single life stages in con-
trolled incubation chambers at six constant tem-
peratures, i.e., 15, 20, 25, 30, 35, and 40 °C. A
group of 25 newly emerged crawlers (0–24-h
old) of P. solenopsis was transferred into a small
plastic jar (10 × 7.5 cm) containing a medium
sized sprouted potato tuber. The jar was covered
with a muslin cloth tied with rubber band. The
experimental setup was replicated six times with
a total of 300 individuals tested at each temper-
ature. The development and survival of insects
were recorded daily by observing them under
stereomicroscope. The similar procedure was
followed for second- and third-instar mealybugs.
The development time and mortality of nymphs
during each instar was recorded daily. In P. so-
lenopsis, the immature intended to develop as
males construct a loosely woven silky filamen-
tous cocoon after second moult and undergoes
two moults inside with a prepupal stage, before
emerging as winged adults. Hence, 20 newly
woven cocoons were separated and observed for
emergence at each test temperature in ten repli-
cations. For recording fecundity and longevity,
newly moulted six adult females (0–24-h old)
from the colony of P. solenopsis were confined
separately to a plastic jar (10 × 7.5 cm size) con-
taining a sprouted potato tuber covered with
muslin cloth. The experiment was repeated five
times. Similarly, freshly emerged winged adults
from puparia were observed for their longevity
at respective temperatures. The survival time was
recorded separately for males and females.
Mode Fitting and Analysis
For simulating temperature-dependent life table
parameters of P. solenopsis, we used Insect Life
Cycle Modeling Software (Version 3.0), de-
veloped by International Potato Center, Lima,
Peru (Sporleder et al. 2012 ). Overall phenology
models were established using best fitting func-
tions in a rate summation and cohort up-dating
approach. Cumulative frequency of development
time of each life stage and temperature was plot-
ted against normalized development times, i.e.,
time/median development time by fitting a log-
normal distribution curve. Sharpe and DeMichele
model (Sharpe and DeMichele 1977 ; Schoolfield
et al. 1981 ) was used for describing temperature
dependence of mean development rates of imma-
ture stages and adult senescence. The equation of
model is:where r ( T) is the development rate at tem-
perature T (°K), R is the universal gas constant
(1.987 cal degree−1 mol−1), RHO 25 is the devel-
opment rate at 25 °C temperature (298.16 °K),
assuming no enzyme inactivation, ΔHa is the en-
thalpy of activation of reaction catalyzed by en-
zyme (cal mol−1), ΔHl is the change in enthalpy at
low temperature (cal mol−1), ΔHh is the change in
enthalpy at high temperature (cal mol−1), Tl is the
low temperature at which enzyme is half active
and Th is the high temperature at which enzyme
is half active.
A second-order polynomial function [m
(T) = aT^2 + bT + c, where m (T) is the mortality
or fecundity at temperature T (°C)], was fitted
to describe temperature dependence of immature
mortality and female fecundity. Age-related ovi-
position rate was described by exponential model
[y = (1−exp (−(ax + bx^2 + cx^3 ))), where y is the cu-
mulative oviposition rate, and x is the normalized
female age].025 exp^11
() 298.16 298.16 ,
1 exp^11 exp 1 1RH T Ha
rT RT
Hl Hh
R Tl T R Th T××−∆
=
+−+−∆∆