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Entomotoxic Effect of Cheese Wood against Cowpea Bruchid,
Callosobruchus maculatus
(Fab.)
11
chemical insecticides have not commanded more than
1% of the global insecticide market (Isman, 2000;
Begum et al., 2013) because they are believed to be
short live and loss their potency over time (Oruonye
and Okrikata, 2010). For these reasons, there is need
to search for other plants which could comparably
contend with synthetic chemical insecticides since
tropical region of the world including Nigeria are well
endowed with numbers of plant species that could
have insecticidal properties. Therefore, this study
investigated the bio-efficacy of crude extracts from
Cheese wood,
A. boonei
as a surface protectant against
cowpea bruchid,
C. maculatus
, attacking cowpea
seeds in storage.
1 Material and Methods
Newly emerged adult
C. maculatus
used for this study
were obtained from already existing culture in the
Postgraduate Research Laboratory of the Department
of Biology, Federal University of Technology, Akure,
Nigeria. They were subsequently reared inside 1 litre
Kilner jars, on un-infested cowpea seeds
Vigna
unguiculata
variety Ife brown obtained from
International Institute for Tropical Agriculture, Ibadan,
Nigeria. The culture was placed in an insect rearing
cage at ambient temperature of (28+2)
℃
and
(75+5)% relative humidity.
Leaf, stem bark and root of
Alstonia boonei
used for
this study were sourced fresh from Akola farm at
Igbara-Odo Ekiti, Ekiti State, Nigeria. These plant
parts were rinsed in clean water to remove sand and
other impurities, cut into smaller pieces before
air-dried in the laboratory. The cleaned dried plant
parts were pulverised into very fine powder using an
electric blender (Supermaster ®, Model SMB 2977,
Japan). The powders were further sieved to pass
through 1mm
2
perforation. The powders were packed
in plastic containers with tight lids and stored in a
refrigerator at 4
℃
prior to use.
For extraction by the kneading method, 800 g of each
of the pulverised plant parts were weighed into a
plastic bowl. Pre-boiled water was added gradually,
a little at a time, from a kettle and mixed with
A.
boonei
powders. The procedure was repeated until a
dough-like material was formed. The extract of
A.
boonei
leaf, stem bark and root were pressed out
manually with hand and poured into a 250 ml
volumetric flask and stored at room temperature. From
this stock, 0.3 ml of
A. boonei
leaf, stem bark and root
extracts were used.
0.3 ml of each extracts of
A. boonei
was mixed
separately with 20 g of un-infested cowpea seeds in
250 ml plastic containers. The extracts and seeds were
thoroughly mixed using a glass rod and then agitated
for 5~10 min to ensure uniform coating. Control
experiments were also set up. Ten pairs of teneral
adult
C. maculatus
were introduced into each of the
containers and covered. Four replicates of the treated
and untreated controls were laid out in Complete
Randomized Design in insect cage. Beetle mortality
was observed daily for 4 days. The beetles were
confirmed dead when there was no response to
probing with sharp pin at the abdomen. The total
number of eggs laid per replicate was recorded after 4
days post treatment. Percentage adult mortality was
corrected using Abbott (1925) formular thus:
P
O
-
P
C
100
P
T
=
—————×
——
100 – P
C
1
Where P
T
=corrected mortality (%)
P
O
=observed mortality (%)
P
C
=control mortality (%)
The experimental set up was kept inside the insect
rearing cage for further 30 days for the emergence of the
first filial (F
1
) generation. The percentage number of
adult beetle emergence was calculated according to the
method described by Odeyemi and Daramola (2000).
The percentage reduction in adult emergence of F
1
progeny or inhibition rate (IR) was calculated according
to the method described by Tapondju et al. (2002).
C
n
-
T
n
100
% IR=
————×——
C
n
1
Where C
n
is the number of emerged insects in the