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Rufai Oladimeji
Lagos State University
100Level, Nigeria.
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A biochemistry doctoral student at the
University of Ibadan, Mojisola Karigidi, who
is the founder of Moepelorse Bio Resources,
has produced a bio-pesticide for preserving
beans, pulses and grains.

Giving the background to her pet research
product, Karigidi said “weevils that attack
beans and maize in storage can destroy as
much as 40 per cent of these crops, causing
huge loss to farmers and traders.”Farmers and
food crop traders who are mostly uneducated,
she added, indiscriminately apply insecticides
to these crops in storage to minimise or
eliminate losses as much as possible.

That practice has serious health and
environmental implications, so said the
researcher while speaking with The Guardian.

“So, as a biochemist working on medicinal
plants, I decided to investigate and develop a
plant-based bio-pesticide to get rid of insect
pests that attack food crops in storage,
particularly beans and maize weevils using
lemongrass leaves.” She said lemongrass is
used locally for the treatment of mild fever,
malaria and is also used in green tea products
because of its medicinal properties. It has a
long record of extensive therapeutic
applications in traditional medicine in many
countries across the globe.

“Apart from its medicinal properties, some
people believe that growing the plant around
their home can prevent the invasion of snakes
and other reptiles. This belief motivated my
team members and I to investigate the
insecticidal ability of the plant against weevils,”
she explained.

Product formulation

The researchers obtained the distillate of
lemongrass by a distillation process and
treated weevil-infested beans with different
concentrations of the distillate. Prior to this,
they reared beans weevils to breed them in
large quantities for use. “The result was
interesting, as we recorded the death of adult
weevils within a short while. I thought of
strengthening this effect by combining other
botanicals like orange distillate for example, to
produce a cocktail effect. The bio-pesticide
formulated from this yielded 100 per cent
weevil mortality within one hour of exposure,”
she disclosed.

In another experiment, the researcher infested
clean bean seeds that were without eggs with
weevils and allowed the females lay eggs on
the seeds. Female weevils began to lay eggs
within 12 to 24 hours. The seeds containing
visible weevil eggs were divided into groups
and treated with different concentrations of
the formulated distillate and then incubated in
the dark for eight hours at room temperature
to monitor adult emergence.Compared to the
control group that was untreated, the treated
groups showed no emergence of larva or adult
weevils and no reduction in the weight of
treated seeds.

The biochemist said the formulated bio-
pesticide led to the mortality of both weevils
and eggs, adding that further studies were
done to obtain the most effective dosage.

Dosage and method of application

Based on the bio-efficacy of the bio-pesticide
formulation carried out by the Nigerian Stored
Products Research Institute (NSPRI), Ibadan,
Nigeria, 6 ml of the product can effectively
control 100g of weevil infested maize within
30 minutes of exposure. They recorded 100
per cent mortality of maize weevils in 30
minutes. At a lower dosage of 3 ml per 100g
maize, 100 per cent weevil mortality was
achieved after 24 hours of exposure.
For beans weevil control, 30 ml will get rid of
all weevils in 3kg of beans within 30 to 60
minutes of exposure.However, the findings
showed that preservation rather than control is
the better approach for the use of the bio-
pesticide, as it requires smaller quantity of the
product to prevent weevil infestation on clean
seeds and grains than already infested ones.

“So, immediate spraying of sorted harvested
beans or maize grains with little quantity of
the product and allowing to air dry for five to
10 minutes before bagging will effectively
prevent weevil attacks,” the scientist said.

Comparative advantages

Application of the bio-pesticide, both for
control and preventive purposes against weevil
attack, can preserve the treated food item for
up to a year and six months without the need
for re-application. Re-application is often
needed in the case of the currently used
synthetic pesticides to preserve for this length
of time.

Another advantage, she mentioned, is the well
published medicinal properties of the plant,
including anti-inflammatory, anti-bacterial,
anti-fungal and antioxidant properties, which
are also beneficial to humans.


The scientist said there was no recorded health
implication for the consumption of
lemongrass-treated food items, although there
may be individual allergy to the lemongrass
smell of the product.

Mode of action

The insecticidal and ovicidal effects of the bio-
pesticide occur through inhalation and contact.

The terpenes and terpenoids, which are plant
secondary metabolites present in the plant
formulation, cause symptoms that suggest a
neurotoxic mode of action on treated beans
and maize weevils. On prevention of weevil
infestation, the lemony smell of the product
repels weevils, thereby preventing their attack
and the possibility of laying eggs.

Product barrier and its commercialisation

The chief developer of the product said the
present barrier to the commercialisation of the
product, which has been patented under the
Trademarks, Patents and Designs Registry of
the Federal Ministry of Industry, Trade and
Investment of the Federal Republic of Nigeria,
is the cost price.

She estimated that selling price is relatively
higher when produced at the small-scale level,
but upon licensing to big manufacturers,
production cost would be reduced when
material extraction is done large-scale. That
way she said, the product could be made
available to farmers, traders and households at
affordable and competitive rates, especially for
organic products.

Mojisola Karigidi was a 2017 Aspen New Voices
fellow and a 2016 fellow of the Mandela
Washington fellowship programme. She was
selected as a 2014 fellow of the African
Women in Agricultural Research and
Development (AWARD) and became an awardee
of the Global Innovation through Science and
Technology (GIST Tech-I) competition in 2015
based on the lemongrass pesticide. She holds a
Master’s degree in Biochemistry from the
University of Ibadan.

Ui Student Develops Lemongrass- Based Insecticides Against Beans Weevils  - Career & Motivation

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