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International Journal of Horticulture 2014, Vol.4, No.9, 44
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49
http://ijh.biopublisher.ca
47
Table 5 Effect of oil of three cultivars of capsicum spp. extracted with different solvents on
S. zeamais
and it infestation at 10.0 ml dosage
Plant materials
Solvent used
Mean±S.E of each parameter
Mortality (%)
Adult emergence
Damage (%)
Weight loss (%)
Cayenne pepper
N-hexane
Ethanol
Acetone
100.00±0.00ef
83.75±2.39ef
73.75±6.25de
0.00±0.00a
2.00±0.41ab
3.00±0.41ab
0.00±0.00a
2.67±0.55ab
4.02±0.55ab
0.00±0.00a
0.31±0.12a
0.49±0.20a
Sweet pepper
N-hexane
Ethanol
Acetone
45.00±5.40bc
33.75±4.73b
27.50±7.77b
4.75±0.95bc
8.75±1.49cd
11.50±0.65e
6.34±1.28abc
11.62±1.90cd
15.18±0.84d
3.31±1.04a
4.20±0.39a
5.10±0.11a
Long-cayenne pepper
N-hexane
Ethanol
Acetone
65.00±6.12de
62.50±2.39de
56.25±2.39cd
3.75±1.03abc
5.25±0.75bc
7.00±1.41bcd
3.35±1.14ab
7.01±0.97bc
9.34±1.88cd
0.29±0.11a
0.49±0.11a
0.62±0.21a
Controls
N-hexane control
Ethanol control
Acetone control
Untreated control
0.00±0.00a
0.00±0.00a
0.00±0.00a
0.00±0.00a
48.50±1.71e
51.00±0.82e
51.00±0.82e
50.25±1.49e
65.50±2.04e
68.48±1.51e
68.48±1.51e
68.48±1.51e
88.34±2.99b
96.04±1.78b
96.04±1.78b
96.04±1.78b
Note: Each value is mean±S.E of four replicates; Means that carries the same alphabet within the same column are not significantly
(p<0.05) different from each other using Turkey’s Test
Discussion
Use of plant materials has remained the major
weapons among the tropical zones farmers even
before the discovery and commercial success of
nowadays synthetic chemical insecticides. However,
consumers seem to reject many food commodities
treated with these botanical materials especially their
extracts which are believed to be more effective than
their powders. This is because of the unpleasant effect
such as obnoxious odour, change in taste and change
in colour pose by these extracts (Begum et al., 2013).
Therefore, acceptable method of application such
fumigation is required. Nevertheless, Okosun and
Adedire (2010) noted that ability of a botanical extract
to contain its active compounds depends on the types
of solvent used for their extraction.
The result obtain from this work showed that all the
extracts of the three
Capsicum
spp
.
tested showed a
greater significant fumigant effect on the different life
stages of
S. zeamais
when compared to the controls
especially at the higher dosages. However, n-hexane
extracts of these pepper cultivars showed more
insecticidal bustle than ethanol and acetone extracts of
these cultivars. The high adult insect mortality
recorded by these extracts could be due to the ability
of the fumes of the oils to block the breathing
organelle (spiracle) of the insect and thereby led to
suffocation and subsequent death of the insects.
However, none of the oil extracts used as fumigant
was able to prevent the emergence of the adult weevil,
seed damage and weight loss regardless of the dosage
used and solvent used for their extraction. The
fumigants (oil extracts) nevertheless have a greater
insecticidal effect on the emergence of the adult
weevil and ability of the weevil to cause seed damage
and weight loss with the acetone extract of the
Capsicum
spp
.
showing the lowest effect. This is
agreement with the work of Ofuya and Olowo (2006)
in which the extract of some medicinal plants used as
fumigant were found to significantly reduced adult
emergence of
Calllosobruchus maculatus
on cowpea.
The ability of cultivars of
Capsicum
spp. used as
fumigant could be due to the death of the insect larvae
which may occur due to inability of the larvae to fully
cast off their exoskeleton which remained linked to
the posterior part of their abdomen as suggested by
Oigiangbe et al. (2010). This work also showed that
the fume of cayenne pepper, sweet pepper and long
cayenne pepper have effect on the post embryonic
survival of the
S. zeamais
as they reduced the adult
emergence of the insect at different dosages. Yang et
al. (2006) opined that the secondary metabolites found
in plants have growth disruptive effect on insects and
therefore affect their life cycle. These secondary
metabolites in plants were also found to affect the
survival rate of insects. Therefore, the phytochemicals
such as flavonoid, alkaloid and saponin (Lee et al.,
1995) which are reported to present in these
Capsicum
spp. could responsible for their insecticidal effect on
both adult mortality and emergence. The insecticidal
effects of these oil fumigants could be correlated with