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Entomotoxic Effect of Cheese Wood against Cowpea Bruchid,
Callosobruchus maculatus
(Fab.)
15
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
and A. boonei latex against
C. maculatus
.
In this study,
A. boonei
stem bark extract was the most
toxic to adult
C. maculatus
. The insecticidal potential
of this plant extracts on the cowpea bruchid could be
as a result of the presence of some chemical
compounds of the triterpenoids, indole and alkaloid
group such as alstonine, astondine, and porphine that
have been identified from
A. boonei
(Phillipson et al.,
1987; Anonymous 1992; 2001, Moronkola and Kunle,
2012; Ojo and Ogunleye 2013a; b).
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 effect of the extract 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; b; Ojo and Ogunleye, 2013b). Extracts have
been reported to inhibit locomotion (Adedire et al.,
2011; Ileke et al., 2013); hence, the beetles were
unable to move freely thereby affecting mating
activities and sexual communication (Adedire et al.
2011; Ileke et al. 2012). The inability of the eggs to
stick to the cowpea seed due to the presence of the
extracts also reduced adult emergence arising from
egg mortality (Adedire et al., 2011; Ileke et al., 2013a).
It has been reported that one of the main mechanisms
of action of plant extracts is their ability to penetrate
the chorion of bruchid eggs via the micropyle and
cause the death of developing embryos through
asphyxiation (Don–Pedro 1989a; b). Reduction in
progeny development may be due to early mortality
and partial or complete retardation of embryonic
development (Dike and Mbah, 1992).
The protectability of the extracts was highly
remarkable. The contact toxicity bioassay of
A. boonei
extracts on adult
C. maculatus
observed at 30, 60 and
90 days after treatment revealed the insecticidal
potency of
A. boonei
stem bark extract. This shows
that the
A. boonei
stem bark extract can protect stored
cowpea conveniently for 90 days. Some botanicals
have been tested for long term protectability on
cereals and legumes (Shaaya et al., 1997; Pereira,
1983; Ajayi and Adedire, 2003; Oni, 2009). Shaaya et
al. (1997) tested the toxicity of palm kernel and rice
bran oils on chick peas and mung beans against
C.
maculatus
infestation at rates 1.5 g and 3 g/kg cowpea
seeds and reported full protection for a period of 4 to 5
months. Pereira (1983) studied the effectiveness of six
vegetable oils as protectants of cowpea seeds and
bambara groundnuts against
C. maculatus
at rate 8
ml/kg. He reported a good protection for a period of 3
to 6 months. Ajayi and Adedire (2003) studied the
protectability of sub-ledal doses of
Hura crepitans
seed oil as cowpea protectant against
C. maculatus
at
concentrations 0.25, 0.5 and 1% v/w protected seeds
from been damage by
C. maculatus
for a period of 3
months. Oni (2009) reported the effectiveness of three
local cultivars of pepper,
Capsicum
species as cowpea
protectants at concentrations 0.5 ml/ 20g, 0.1 ml/ 20g,
2.0 ml/ 20g, 5.0 ml/ 20g and 10 ml/ 20g of cowpea
seeds. She reported a good protection for a period of 6
months. All tested concentrations of
A.
stem bark
extract gave protection for a period of 90 days. The
insecticidal potential of
A. boonei
leaf and root oil
extracts was greatly reduced on mortality of adult
C.
maculatus
at 30, 60 and 90 days of post treatment.
This was in agreement with Adedire and Ajayi (1996)
who reported that the toxicity of some plant extracts
used for control of weevils did not persist indefinitely,
some extracts lost their effectiveness within 95 days of
treatment. Oni (2009) also reported that the oil extract
of three local cultivars of pepper,
Capsicum
species
used in protecting maize grains against
Sitophilus
zeamais
, lost their potency after 6 months in storage.
4 Conclusions
This study has further revealed the insecticidal
potential of
A. boonei
extracts obtained by kneading
method as cowpea protectant against
C. maculatus
and could serve as an alternative to synthetic
insecticides for the protection of stored cowpea seeds
against
C. maculatus
or other related insect pests by
local farmers that could not afford or have access to
soxhlet extraction apparatus and rotary evaporator.
The plant is medicinal, readily available, safe, eco –
friendly, biodegradable and they have not been