Temperature-Based Phenology Modeling and GIS-Based Risk Mapping 423
generation lengths for each Julian day as shown
in the following formula:
where Tx is the predicted generation length in
days at Julian day x ( x = 1,..., 365)
c. Activity index (AI)
This index represents the finite rate of increase
and hence population growth potential of given
pest species. It is calculated by taking a log of the
products of the estimated finite rates of increase
for each Julian day as shown in the following for-
mula:
where λx is the finite rate of increase at Julian day
x ( x = 1,..., 365).
GIS Mapping of Risk Indices
The maps showing the pest risk potentials were
visualized by employing the estimated risk indi-
ces in “potential population analysis and map-
ping” module of ILCYM software. The module
GI =365/
365= 1365∑x Tx
,365
10
1AI log ,
xλx
== ∏
facilitates spatial simulations of pest populations
through grid based within a defined area according
to grid-specific monthly temperatures interpolated
from available databases (worldclim in this case).
The estimated indices were organized in matrices
of 12 × 12 dimensions using longitude as columns
and latitude as rows, representing 12 matrices
each for ERI, GI, and AI. The generated ASCII
files (.asc) were converted to grid format by im-
porting in DIVA-GIS, an open-source geographic
information system (downloadable at http://www.
diva-gis.org) for visualizing the risk maps.Results and Discussion
Effect of Temperature on P. Solenopsis
Development of all the immature life stages of
P. solenopsis was significantly affected by the
temperature. Development time decreased sig-
nificantly with increasing temperatures within
the evaluated temperature range (Table 1 ). The
development of immature stages at temperature
extremes (15 and 40 °C) was best described by
nonlinear model, Sharpe and DeMichele func-
tion (for all stages, df = 4, 13; P ≤ 0.001; Nymph
1, F = 173.14; Nymph 2, F = 195.57; Nymph 3,
F = 71.10; Male pupa, F = 182.77) (Figs. 1a, 1b,Table 1 Mean development time and survival of P. solenopsis life stages at constant temperatures (Replications:
nymphs = 12; male pupae = 10; adults = 5; total sample size: nymphs = 300; male pupae = 100; adults = 30)
Tem-
pera-
ture
(°C)
Nymph1 Nymph2 Nymph3 Male pupae Female Male
Mean
develop-
ment time
(days)Survival
(%)Mean
develop-
ment time
(days)Survival
(%)Mean
develop-
ment time
(days)Survival
(%)Mean
develop-
ment time
(days)Survival
(%)Survival
time
(days)Survival
time
(days)15 14.44
(0.11)41.65
(1.82)16.51
(0.12)77.00
(1.67)13.89
(0.12)87.00
(1.13)18.98
(0.10)71.00
(2.07)50.54
(0.59)3.78
(0.06)
20 11.98
(0.10)47.67
(1.95)12.18
(0.10)86.00
(1.21)10.02
(0.10)91.00
(0.83)14.81
(0.08)81.00
(1.91)44.44
(0.51)2.95
(0.05)
25 6.72
(0.06)71.33
(2.40)7.78
(0.06)93.00
(0.87)5.83
(0.06)94.00
(0.85)9.05
(0.06)90.00
(0.91)29.47
(0.40)2.67
(0.05)
30 5.45
(0.05)76.67
(1.60)6.32
(0.05)95.00
(0.86)5.56
(0.06)96.30
(0.91)6.96
(0.05)93.00
(0.81)30.87
(0.35)1.83
(0.04)
35 3.89
(0.05)55.33
(1.46)4.94
(0.05)75.30
(1.51)3.30
(0.04)89.70
(1.01)3.85
(0.04)84.00
(1.05)23.80
(0.19)1.79
(0.04)
40 3.0
(0.04)29.33
(1.50)3.54
(0.04)54.00
(1.28)3.01
(0.05)85.00 3.46
(0.00)79.00 18.44
(0.11)1.41
(0.01)
Numbers in parentheses are standard errors