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International Journal of Horticulture 2014, Vol.4, No.6, 24
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31
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27
Table 6 Phytochemicals in different petroleum extracts of
A. boonei
Phytochemicals
Leaf extract
Stem bark extract
Root extract
Alkaloids
+
+
+
Saponins
+
+
+
Tannins
+
+
+
Phlobatannins
-
-
-
Anthraquinones
-
-
-
Flavonoids
-
+
-
Cardiac glycosides
+
+
+
Note: Key:
-
: Absent; +: Present
2 Discussion
It is evident from the results of this study that among the
three oils tested for insecticidal activity,
A. boonei
stem
bark oil was the most effective in controlling the
population of
C. maculatus
. However, the effectiveness
of
A. boonei
oils were dependent on dosage rate and
period of application. Previous studies by Ileke and Oni
(2011); Ileke et al. (2012); Ileke et al. (2013b); Ileke et
al. (2014a; 2014b) have shown insecticidal activity of
A.
boonei
powders against
Sitophilus zeamais
,
A. boonei
stem bark oil obtained by cold extraction using five
different solvents on the mortality of cowpea bruchid,
C.
maculatus
,
A. boonei
latex and extracts of
A. boonei
obtained by kneading extraction against
C. maculatus
respectively.
A. boonei
stem bark extract completely
protected cowpea seeds against
C. maculatus
infestation
and also prevented oviposition, adult emergence and
reduction in F
1
progeny of
C. maculatus
.
The phytochemicals present in the petroleum extract of
A. boonei
leaf, stem bark and root includes; alkaloids,
saponins, tannins, flavoniods and cardiac glycosides.
Fernando
et al
. (2005) reported that most plants are
known to possess chemical substances like terpenoides,
saponins, tannins, flavonoids and alkaloids among
others which have found to have reasonable efficacy
against insect pests.
Plant alkaloids are a major source of bio-insecticides
especially since the discovery of Azadirachtin from
neem tree,
Azadirachta indica
(Maala et al., 2000;
James et al., 2003; Bruce et al., 2004). The toxicity rate
of
A boonei
stem bark to cowpea bruchid,
C. maculatus
may be as a result of alkanoids which may be more
concentrated in the stem bark of the plant than other
parts. Fasola and Egunyomi (2005) reported that the
major phytochemicals in the stem bark of
A. boonei
are
saponins, alkaloids, tannins, flavonoids and cardiac
glycosides.
Alstonia boonei
bark is known to contain
some chemical compounds of the indole alkaloid group
namely alstonine, porphine and alstonidine as well as
triterpenoids (Phillipson et al., 1987; Anonymous 1992;
2001; Moronkola and Kunle, 2012). Facknath and
Lalljee (2008) reported that alkaloids and tannins from
Ayapa triplinervis
(Vahl) exhibited feeding deterrence
against
Plutella xylostella
and
Crocidolomia
binotalis
. It have been reported that tannins help in
growth regulation and also protect the plants from
predators (Fasola et al., 2013). Flavonoids help in
protecting the plants from microbes and insect attacks
(Fasola et al., 2013). The stem bark of
A. boonei
was the
most effective part for the control of
C. maculatus
and
this was the only part that flavonoids was detected.
The effect of the oil on oviposition could be due to
respiratory impairment which probably affects the
process of metabolism and consequently other systems
of the body of the bruchid (Osisiogu and Agbakwuru,
1978; Onolemhemhem and Oigiangbe, 1991; Adedire et
al., 2011 Ileke et al., 2013a; 2013b; Ojo and Ogunleye
2013b; Ileke et al., 2014b). Oils have been reported to
inhibits locomotion (Adedire et al., 2011; Ileke et al.,
2014b); hence, the beetle were unable to move freely
thereby affecting mating activities and sexual
communication (Adedire et al., 2011, Ileke et al., 2012;
Ileke et al., 2014b).
3 Conclusion
This study has further revealed the entomocidal activity
of
A. boonei
oils extracted by soxhlet method in the
management of
C. maculatus
and could serve as an
alternative to synthetic chemical insecticides.