International Journal of Horticulture 2015, Vol.5, No.4, 1
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11
6
The gross reproductive rate (GRR) of
P.
quatuordecimpunctata
on
S. pinnata
(73.981±1.840)
and
S. dulcis
(71.196±7.725) was without significant
difference (
F
1,4
= 0.123,
P
= 0.743) (Table 9). But net
reproduction rate (R
0
) on
S. pinnata
leaves
(31.160±2.553) was significantly higher than on
S.
dulcis
(19.703±2.993) leaves (
F
1,4
= 8.481,
P
<0.05)
(Table 9). The intrinsic rate of natural increase (r
m
) and
the daily finite rate of increase (λ) were also higher on
S.
pinnata
leaf fed insects (0.036±0.001 and 1.036±0.001
per female per day, respectively) relative to
S. dulcis
(0.031±0.002 and 1.032±0.002 female offspring per
female per day, respectively) leaf feeders (
F
1,4
= 5.151
and 5.167, respectively,
P
=0.085) (Table 9). The mean
generation time (T
c
) of
P. quatuordecimpunctata
on
S.
pinnata
(143.333±0.265) and
S. dulcis
(153.083±0.144)
was significantly differed (
F
1,4
=22.915,
P
< 0.01) (Table
9). Whereas, their doubling time (DT) on
S. pinnata
(31.511±0.436) was slightly higher than on
S. dulcis
(32.984±0.369) but without significant difference
(
F
1,4
= 4.178,
P
= 0.110) (Table 9). Thus, the population
growth parameters of
P. quatuordecimpunctata
were
optimum on
S. pinnata
relative to
S. dulcis
in relation
with their phytochemical regime.
Table 9 Population and reproductive life table of
P. quatuordecimpunctata
on
S. dulcis
and
S. pinnata
leaves
Population Parameter
S.dulsis
S. pinnata
F
(
df
=1,4)
Sig.
Gross reproductive rate (GRR)
71.196±7.725
73.981±1.840
0.123
0.74352
Net reproductive rate (R
0
)
19.703±2.993
31.160±2.553
8.481
0.04359
Mean generation time (T
c
)
153.083±0.144
143.333±0.265
22.915
0.00873
Doubling time (DT)
32.984±0.369
31.511±0.436
4.178
0.11045
Intrinsic rate of increase (
r
m
)
0.031±0.002
0.036±0.001
5.151
0.08577
Finite rate of increase (λ)
1.032±0.002
1.036±0.001
5.167
0.08543
Note: Mean ±SE of 3 observations with
F
and
P
values are representing different significant level (ANOVA), while comparing one
type of host plant as food with the other
2 Discussion
Host plant availability and quality may play a vital
role in pest feeding as well as population dynamics by
affecting immature as well as adult performance
(Applebaum, 1985; Schoonhoven et al., 2005; Roy
and Barik, 2013). Whereas, phytochemicals are the
key factor in nutritional ecology and development of a
phytophagous insect (Slansky and Scriber, 1985;
Dicke, 2000; Schoonhoven et al., 2005; Genc 2006;
Shobana et al., 2010; Roy and Barik, 2013). Host-plant
utilization is influenced by the ability of insect to
ingest, assimilate and convert food into 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 survival of adults
(Awmack and Leather, 2002; Syed and Abro, 2003;
Shobana et al., 2010; Roy and Barik, 2013).
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;
2013). 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, secondary metabolites
including phenols, flavonoids, terpenoids, alkaloids
etc. determine the suitability of the substrate for
exploitation by the herbivores and thus govern host
preferences and acceptability (Harborne, 1994;
Schoonhoven et al., 2005). Consumption of greater
amount of secondary chemicals was found to
significantly reduce adult longevity, fecundity, and
retardation of larval growth (Harborne, 1994;
Schoonhoven et al., 2005; Roy and Barik, 2013).
In the present study, all nutritional indices varied
when
P. quatuordecimpunctata
fed on
S. pinnata
and
S. dulcis
leaves (Tables 2-6). The growth rate (GR) of
insects depends on efficiency of conversion of
digested food (ECD) and its reduction indicates higher
metabolic maintenance cost (Slansky and Scriber,
1985; Xue et al., 2010). The current data reveal that
all the four larval instars and adults of
P.
quatuordecimpunctata
had higher GR on
S. pinnata
leaves (Tables 2-6) due to good nutritional quality
relative to the secondary chemicals (Table 1). The
other feeding indices are also affected by the host
phytochemicals in relation with efficiency of nutrient
