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International Journal of Horticulture 2014, Vol.4, No.9, 44
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49
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the type of solvent used for their extraction since
different solvents have different ability of extracting
the active compounds in plants (Okosun and Adedire,
2010; Patra et al., 2012).
Therefore, the ability of n-hexane extract of
Capsicum
spp. to show efficacy on adult emergence of
S.
zeamais
than ethanol and acetone extract of the
peppers may be due to the high extraction capacity of
the solvents. The findings of Patra et al. (2012) and
Zeeshan et al. (2012) in which methanolic extracts of
some plants were found to be effective against
Staphylococcus epidermidis
than other extracts was in
agreement with this work.
The fumigants of these oils of cultivars of
Capsicum
spp
.
significantly reduced the weight loss and damage
of treated seeds. This reduction in weight loss may be
due to the inability of the larvae of the weevil to feed
on the treated maize grains. Similar observation has
been reported by Jayakumar et al. (2003) on cowpea
seeds treated with plant materials. Cayenne pepper,
sweet pepper and long cayenne pepper could serve as
alternative to the use of synthetic chemical
insecticides moreso they are highly medicinal and
being used on daily bases throughout the world.
However, the n-hexane extract of cayenne pepper
could be more preferable as fumigant since it shows
more insecticidal effect than other extracts.
Materials and Methods
Insect culture
The culture of
S. zeamais
was obtained from an
infested maize grain at Entomology Research
laboratory of the Crop, Soil and Pest Management
Department, Federal University of Technology, Akure,
Nigeria. This was reared on non-infested clean maize
grains obtained from Agricultural Development
Project (ADP) Akure, Nigeria. The experiment was
setup in the laboratory at temperature of 28±2
o
C and
relative humidity of 75%±5%.
Collection of plant materials and maize seeds
The three varieties of pepper used were bought from
Oba market in Akure, Ondo State, Nigeria. Collected
pepper varieties were taken to botanist in the
Department of Crop, Soil and Pest Management.
The T-swan variety of maize grains used for the
experiment was obtained from the Agricultural
Development Project (ADP), Akure, Nigeria. The
seeds were cleaned of foreign matter and disinfested
by keeping in freezer at -5
o
C for 7 days. They were
then allowed to air-drying order to avoid mouldeness
of the grains.
Preparation of plant extracts
The pepper cultivars (cayenne pepper, sweet pepper
and long-cayenne pepper) used was collected fresh
and sun dried. The peppers were ground into fine
powder with electric blender and the powders were
further sieved to pass through 1mm
2
perforations
before being stored in separate glass containers with
tight lids for subsequent use. To extract the oils of
these peppers, twenty grammes of each pulverized
pepper varieties was put in a muslin cloth and
transferred into the thimble and extracted separately
with hexane, ethanol and acetone in a soxhlet
apparatus. The extraction was carried out for 3-4hr
depending on the pepper varieties. The extraction was
terminated when the solvent in the thimble becomes
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. The extracted oils were
exposed to air to remove all the traces of volatile
solvents as the will help to avoid false concentrations.
From this main stock solution, different dosages of 0.5
ml, 1.0 ml, 2.0 ml, 5.0 ml and 10.0 ml of each pepper
varieties were made.
Fumigant toxicity of oil extracts
Twenty grammes of maize grains were weighed into
muslin cloth and were infested with twenty unsexed
0~24 hr old adult
S. zeamais
before being tied. The
infested maize grains were hung to the top of 250 ml
plastic containers containing the pepper extracts at
dosage of 0.5 ml, 1.0 ml, 2.0 ml, 5.0 ml and 10.0 ml.
The oil extracts were placed at the bottom of the
plastic containers and it was ensured that the oils were
not in contact with the maize grains hung at the top of
the containers. Two control experiments were set up,
one container with solvent alone and another with
neither solvent nor extract (untreated control). The
experiments were arranged in a complete randomized
design and each treatment was replicated four times.
Adult mortality was observed after of exposure. Both
dead and live insects were removed on the seventh
day and experiments were left for 42days to allow for
emergence of F
1
generation and the number of adult
emerged was counted. The percentage weight loss and