International Journal of Horticulture, 2017,Vol.7, No.2, 7-19
14
secondary chemicals. The other feeding indices are also affected by the host phytochemicals in relation with
efficiency of nutrient digestion or absorption in their metabolic process. Thus, all the instars including adults were
efficiently converting
S. melongena
leaves followed by
S. nigrum
and
M. cochinchinensis
leaves into their
biomass by homeostatic adjustment in consumption rates and other efficiency parameters of the insect for ideal
growth and development (Roy and Barik, 2012; Roy and Barik, 2013; Roy, 2014).The food utilization indices
ultimately influence developmental duration, adult longevity, fecundity and survival of
E. vigintioctopunctata
.
High survival rates and shorter developmental timeof
E. vigintioctopunctata
on
S. melongena
indicates better
nutritional quality of their leaves followed by
S. nigrum
and
M. cochinchinensis
(Slansky and Scriber, 1985; Roy
and Barik, 2012; Roy and Barik, 2013; Roy, 2014; Roy, 2015a). Therefore, it can be concluded that
S. melongena
leaves provides the best quality food to
E. vigintioctopunctata
(higher nutritional factors relative to the
anti-nutritional secondary metabolites) followed by
S. nigrum
and
M. cochinchinensis
for their better nutritional
ecology and population growth.
In ecological research, life table study is a central theme and used to calculate the vital statistics of pest population
dynamics including comprehensive description of their survivorship, development, fecundity, mortality and life
expectancy (Southwood, 1978; Carey, 2001; Sarfraz et al., 2007; Ali and Rizvi, 2008; Roy, 2015b; Dutta and Roy,
2016). It is widely useful technique in insect pest management, where developmental stages are discrete and
mortality rates vary widely from one life stage to another (Kakde et al., 2014; Roy, 2015b; Dutta and Roy, 2016).
There is a range of innet capacity for individual of a population (Gill et al., 1989; Roy, 2015b; Dutta and Roy,
2016) but the variation in available food quality (Kim and Lee, 2002; Liu et al., 2004; Yasar and Güngör, 2005;
Win et al., 2011; Roy and Barik, 2012; Roy and Barik, 2013; Roy, 2014; Roy, 2015a) along with environmental
factors (Ellers-Kirk and Fleischer, 2006; Schowater, 2006; Ali and Rizvi, 2010) always influence the growth,
reproduction, longevity and survival of that population. The effect of different food sources on population
parameters were observed in
Epilachna dodecastigma
(Khan et al., 2000),
E. sparsa
(Abbas and Nakamura, 1985),
Plutella xylostella
(Sarfraz et al., 2007) and
Diacrisia casignetum
(Roy and Barik, 2013) on different host plants.
Variation between the results of this study could be attributed to differences among nutritional and anti-nutritional
factors present in the respective host leaves that directly affect potential and achieved herbivore development and
fecundity (Awmack and Leather, 2002; Syed and Abro, 2003; Roy and Barik, 2012; Roy and Barik, 2013; Roy,
2014; Roy, 2015a).
The overall accumulated survival rate of
E. Vigintioctopunctata
on
S. melongena
leaves was highest as compared
with that on
S. nigrum
and
M. cochinchinensis
leaves and the result suggest type III survivourship curve like most
insect species (Price, 1998; Schowalter, 2006; Roy, 2015b; Dutta and Roy, 2016). The GRR, R
0
, r
m
, T
c
, DT and λ
are fundamental ecological parameters to predict the pest population growth to evaluate the performance of an
insect on different host plants as well as their resistance (Southwood and Henderson, 2000; Win et al., 2011; Roy,
2015b; Dutta and Roy, 2016). In the present study, GRR, R
0
, r
m
, and λ of
E. vigintioctopunctata
was significantly
higher on
S. melongena
followed by
S. nigrum
and
M. cochinchinensis
leaves. Whereas, the T
c
and DT was also
significantly lower on
S. melongena
than on
S. nigrum
and
M. cochinchinensis
leaves. Thus, the population
parameters of
E. vigintioctopunctata
on the three host leaves will help to assess the relative contribution made by
the respective leaf constituents to the adult population pool. This knowledge of nutritional ecology along with the
life table parameters of
E. vigintioctopunctata
can help one to understand their population dynamics for their
proper management for sustainable agriculture of those crops.
In respect to the phytochemical regime,
S. melongena
leaves had the lowest antibiosis resistance against
E.
vigintioctopunctata
and were the most favorable one relative to
S. nigrum
and
M. cochinchinensis
as indicated by
the short developmental time (T
c
and DT), which leads to reduce exposure of the insect to its natural enemies, and
high survival of immature stages. By knowing such most vulnerable stages (egg and pupal stages) from the life
table parameters, one can also make time based application of different control measures for proper management
of that pest population. Ultimately, the Knowledge on their population growth as well as their nutritional ecology
in relation with respective host leaf chemicals support the use of
S. nigrum
as an alternative host towards
S.
melongena
and as a trap crop towards
M. cochinchinensis
to avoid or minimum invasion of this pest for
sustainable agriculture.
