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Molecular Entomology
35
Collection of wheat seeds and plant materials
The wheat seeds used for this study were collected
from the Agricultural Development Project (ADP),
Akure. The seeds were cleaned of foreign matter and
disinfested by keeping in freezer at -5
o
C for 7 days.
They were subsequently exposed to air to reduce their
moisture before being used for the experiments. The
E.
aromatica
seeds used were purchased from local
herbal seller in Oba market Akure, Nigeria. The
seeds of
E. aromatica
were sundried and pulverized
into fine powder using an electrical grinder (model
373) and were kept in air-tight plastic containers for
subsequent use.
Preparation of oil extract
Twenty grams of each pulverized plant materials was
put in a muslin cloth and transferred into the thimble
and extracted with methanol in a soxhlet apparatus.
The extraction was carried out for 3-4hr and the
extraction was terminated when the solvent in the
thimble become clear. Then, the thimble was removed
from the unit and the solvent recovered by distilling in
the soxhlet extractor. The resulting extracts contain
both the solvent and the oil. The solvent was separated
from the oil using rotary evaporator, after which the
oil was exposed to air so that traces of the volatile
solvent evaporates, leaving the oil extract.
Preparation of the storage material
The storage material used was jute bag. The jute bags
of 1x1 mm mesh size were cut into sizes (30cm by
30cm), all the sides were sewed and one side was left
open through which the samples were filled into the
bags. These bags were separately sprinkled with oil of
E. aromatica
using graduated syringes at doses of 2, 4,
6 and 8ml. The bags were air dried for 2 days in the
laboratory before use. Another set of bags were deeply
soaked in 100ml of
E. aromatica
oil. Untreated bags
and bags that were treated with 8ml of solvent
(methanol) were set as controls.
Experimental procedures
200 grams of wheat seeds were weighed into each
treated jute bag. Twenty 0-24 hours old unsex adults
of
R. dominica
were introduced into the treated bags
containing wheat. The experiment was set up in a
complete randomized design. Each treatment had
seven replicates. The bags were tightly sealed by
sewing with needle and thread. Mortality was
observed at interval of 24, 48 and 72hours. All dead
and live insects were removed after 72hours of
exposure and the bags were sealed again to determine
the number of F
1
adult emerged, % adult inhibition
rate (%IR), weight loss and level of seed damage after
42 days of storage. The bags were tightly sealed after
the observation of the number of emerged adult, seed
weight loss and seed damage at 42 days of storage and
was left for 6 months after which only the seed weight
loss and damage was determined. The formula below
was used to calculate the percentage inhibition rate,
percentage weight loss and percentage damaged seeds
respectively.
Tapondju
et al.
(2002)
Where C
n
is the number of insects that emerged in the
control treatment and T
n
is the number of adult insects
that emerged in the treated grains.
The effect of the
E. aromatica
oil used for the
treatment of the jute bags on the protected wheat
grains were assessed after six months of storage. This
was done by subjecting the grains for assessment by
ten different panelists. The panelists observed the
effect of the oil on the colour and odour of the grains.
Viability bioassay
After six months of storage thirty seed of stored wheat
were randomly picked from each treated jute bags and
were separately placed on moist whatman filter paper
No. 1 inside disposable Petri dishes at the rate of 10
seeds per plate kept in a Gallenkamp incubator.
Emerged seedlings were counted at the end of 7 days
after planting and % viability was calculated as follow: