International Journal of Horticulture, 2018, Vol.8, No.1, 1-7
2
(Isman, 2006). Currently, research efforts are focused on the use of botanical products as alternatives to synthetic
insecticides. These plant products which include ashes, plant powders, extracts and oils have been confirmed to
be cheaper, safe, and eco-friendly (Adedire
et al
., 2011; Ojo and Ogunleye, 2013). There is no doubt that
botanical insecticides are an interesting alternative to insect pest control, and on the other hand only a few of the
more than 250,000 plant species on our planet have been properly evaluated for this purpose (Khalequzzaman
and Osman Goni, 2009). Use of plant products for infestation control in stored grains therefore seems to offer
desirable solutions, especially in developing tropical countries where plants are found in abundance everywhere
throughout the year (Khalequzzaman and Osman Goni, 2009).
Securidaca longepedunculata
(Fres.) is a semi deciduous shrub used as a traditional medicine in many parts of
Africa against a number of invertebrate pests, including insects infesting stored grains (Burkill, 1997). In Africa
(Ghana; Nigeria) the plant decoction is prescribed by Ghananian healers to treat asthma and other diseases
associated with smooth muscle contraction (Rakuambo
et al
., 2006). In Nigeria, extracts from various parts of the
plants has been reported to possess both gastrointestinal and trypanocidal effects (Olajide
et al
., 1999).
1 Materials and Methods
1.1 Preparations of
Callosobruchus maculatus
cultures
The culture of
Callosobruchus maculatus
was obtained from naturally infested cowpea seeds,
Vigna unquiculata
Walp bought from Oja-Oba Market in Ikole-Ekiti, Ekiti- State, Nigeria. The adult C. maculatus were cultured in
the laboratory on clean uninfested Ife brown variety collected from Agricultural Development Project (ADP),
Ikole Ekiti, Ekiti State, Nigeria. 750 g of the cowpea seeds was measured into a Kilner jar, thereafter, twenty (20)
pairs of adult
C. maculatus
(10 male :10 female) were introduced into the Kilner jar covered with muslin cloth to
let in air but prevent the escape of beetles (Jambere
et al
., 1995). The insects were allowed to lay eggs seven (7)
days. After that all the insects both alive and dead were then removed to allow new generations to emerge and
after 28 days of adult removal, the progeny that emerged were used for re-culturing. Subsequently, insects that
emerged were used for the different experiments. Insect rearing and the experiment were carried out at the
laboratory, Department of Crop Science and Horticulture, Federal University Oye Ekiti (FUOYE), Ekiti State,
Nigeria at ambient temperature of 28±2
0
C and 75±5 % relative humidity.
1.2 Collection of plant materials and cowpea seeds (
Vigna unquiculata
)
The plants evaluated for insecticidal activity were
Securidaca longepedunculata
(leaf, stem-bark and
root-bark)).These plant parts were collected from a farmland along Itapaji Ekiti, Ekiti State and taken into the
laboratory. The root bark and stem bark were washed thoroughly with water and cut into small pieces. The plant
parts are then air-dried in the laboratory for 30 days. Each plant part was pulverized separately into fine powders
using Professional Blender (JTC OmniBlendV, Model TM-800). The powders were further sieved to pass through
a 40 mesh sieve and kept in the refrigerator to retain its quality before use. The Ife brown variety of cowpea seeds
used for the experiment was bought from the Agricultural Development Project (ADP), Ikole Ekiti, Ekiti State,
Nigeria. The seeds were cleaned of foreign materials and disinfested by keeping in deep freezer at -5
0
C for 168 h
to kill all hidden infestations. This is done because all the life stages, especially the eggs are very susceptible to
cold (Koehler, 2003). The disinfested cowpea seeds were then air dried in the laboratory to prevent mouldiness
(Adedire
et al
., 2011).
1.3 Contact toxicity assay
To assess the toxic effects of the plant powders on
C. maculatus
, twenty grammes (20 g) of clean and disinfested
cowpea seeds of susceptible Ife brown were weighed using Electronic balance (Model XY3000C) into 160 ml
plastic cups. After this, 0.2 g, 0.4 g, 0.6 g, 0.8 g and 1.0 g of the pulverized plant powders was weighed and
mixed with the cowpea seeds. Plastic cups were shaken thoroughly to ensure adequate mixing of cowpea seeds
and plant powders. 20 newly emerged adults of
C. maculatus
(0-2 day old) were introduced into each of the
treatments. Each treatment was replicated four times. The control experiment had only the cowpea seeds and
beetles i.e no plant powder was involved in the control experiment. The mortality of the beetles was monitored
