International Journal of Horticulture, 2017,Vol.7, No.2, 7-19
13
Table 10 Stage-specific pooled life table of
Epilachna vigintioctopunctata
Fab. on
Momordica cochinchinensis
leaves (Mean of 3
observations)
Parameters
Egg
lnst- I
lnst- II
lnst- III
lnst- IV
Pupa
Adult
lx
0.294
0.228
0.206
0.172
0.150
0.128
0.106
dx
0.067
0.022
0.033
0.022
0.000
0.022
0.001
qx
0.226
0.098
0.162
0.129
0.000
0.174
0.001
sx
0.774
0.902
0.838
0.871
1.000
0.826
1.000
Lx
0.261
0.217
0.189
0.161
0.150
0.117
0.106
Tx
1.639
1.431
1.214
1.025
0.864
0.275
0.158
ex
5.566
6.280
5.905
5.952
5.759
2.152
1.500
kx
0.111
0.045
0.077
0.060
0.000
0.083
0.001
The GRR, R
0
, r
m
and λ of
E. vigintioctopunctata
on
S. melongena
(93.531, 16.630, 0.048 and 1.049, respectively)
was significantly (
P
<0.001) higher than
S. nigrum
(72.828, 11.730, 0.042 and 1.042, respectively) and
M.
cochinchinensis
(53, 5.594, 0.029 and 1.029, respectively) (Table 11). While, the T
c
and DT of
E.
vigintioctopunctata
on
M. cochinchinensis
was significantly (
P
<0.001) higher (60.3 and 24.275 days, respectively)
than on
S. nigrum
(59.40 and 16.720 days, respectively) and
S. melongena
(59.10 and 14.573 days, respectively)
(Table 11). Ultimately, the overall GS was higher on
S. melongena
(0.582) followed by
S. nigrum
(0.568) and
M.
cochinchinensis
(0.550) which was the reflected reverse value of K (0.290, 0.308 and 0.376, respectively). Thus,
the population growth parameters of
E. vigintioctopunctata
were optimum on
S. melongena
relative to
S. nigrum
and
M. cochinchinensis
in relation with their respective phytochemical regime.
Table 11 Population and reproductive parameters of
Epilachna vigintioctopunctata
Fab. on
Solanum melongena
,
S. nigrum
and
Momordica cochinchinensis
leaves (Mean of 3 observations)
Population Parameters
S. melongena
S. nigrum
M. cochinchinensis
Gross reproductive rate (GRR)
93.531
72.828
53.000
Net reproductive rate (R
0
)
16.628
11.733
5.594
Mean generation time (T
c
)
59.100
59.400
60.300
Doubling time (DT)
14.573
16.702
24.275
Intrinsic rate of increase (
r
m
)
0.048
0.041
0.029
Finite rate of increase (λ)
1.049
1.042
1.029
2 Discussions
Host plant availability and quality in terms of their phytochemicals may play a vital role in pest feeding preference
as well as population dynamics by affecting immature and adult performance (Applebaum, 1985; Slansky and
Scriber, 1985; Dicke, 2000; Schoonhoven et al., 2005; Genc, 2006; Shobana et al., 2010; Roy and Barik, 2012;
Roy and Barik, 2013; Roy, 2014). Host-plant utilization is also influenced by the ability of insect to ingest,
assimilate and convert food into their body tissues (Scriber and Slansky, 1981; Dadd, 1985; Nation, 2001). Thus,
host plant quality during larval growth and development is a key determinant of adult longevity, fecundity, fertility
and survivability (Awmack and Leather, 2002; Syed and Abro, 2003; Shobana et al., 2010; Roy and Barik, 2013;
Roy, 2014; Roy, 2015a). Ultimately, shorter developmental time along with greater total reproduction of insects on
a host indicate greater suitability of a host plant (Roy and Barik, 2012; Roy and Barik, 2013; Roy, 2014; Roy,
2015a).The primary metabolites (carbohydrates, proteins, lipids, amino acids including moisture content) are used
for general vitality, growth and reproduction (Mattson, 1980; Dadd, 1985; Slansky and Scriber, 1985; Turunen,
1990; Harborne, 1994; Genc and Nation, 2004; Schoonhoven et al., 2005; Shobana et al., 2010). Whereas, the
secondary metabolites govern the suitability of the substrate for herbivores host preference and acceptability
(Harborne, 1994; Schoonhoven et al., 2005; Roy and Barik, 2012; Roy and Barik, 2013; Roy, 2014; Roy, 2015a).
Consumption of greater amount of secondary chemicals was also found to significantly reduce the adult longevity,
fecundity, and retardation of larval growth (Harborne, 1994; Schoonhoven et al., 2005; Roy and Barik, 2012; Roy
and Barik, 2013; Roy, 2014) due to higher metabolic costs (Xue et al., 2010).
In the present study, all nutritional indices varied when
E. vigintioctopunctata
fed on
S. melongena
,
S. nigrum
and
M. cochinchinensis
leaves. The current data reveal that all the four larval instars and adults of
E.
vigintioctopunctata
had higher GR on
S. melongena
leaves due to good nutritional quality relative to the
