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African Journal of Environmental Economics and Management ISSN 2375-0707 Vol. 11 (1), pp. 001-006, 
January, 2023. Available online at www.internationalscholarsjournals.org © International Scholars Journals 

 

Author(s) retain the copyright of this article. 
 

 

 

Full Length Research Paper 

 

Plant Extracts as Natural Insecticides: A Study on 

Bean and Maize Weevils 
 

O. O. Ogunsina1*, M. O. Oladimeji2 and L. Lajide1
 

 
1
Department of Chemistry, Federal University of Technology, Akure, Ondo State, Nigeria. 

2
Joseph Ayo Babalola University, Ikeji-Arakeji, Osun State, Nigeria. 

 
Accepted 18 November, 2023 

 
A study was conducted to evaluate the insecticidal action of hexane extracts of three locally available plants 
namely: Lantana camara (Verbenaceae), African nutmeg [Monodora myristica (Gaerth) Dunal] and Enuopiri 
[Euphorbia lateriflora, Schum and Thonner] against bean weevil Callosobruchus maculatus (F.) and maize 
weevil, Sitophilus zeamais) Motsch with response to the insect mortality. Results revealed that all test materials 
exhibited mortality action against bean weevil and maize weevil. African nutmeg extracts had greater mortality 
action against both the beans weevil (100%) and maize weevil (96%) after 24 h of treatment. Lantana extracts 
were observed to have moderate mortality effect; bean weevil (93%) and maize weevil (73.3%) while Enuopiri had 
average mortality effect; bean weevil (46.7%) and maize weevil (50%) all with extract concentration of 10 g/100 
ml (extract/solvent). The overall results showed that bean weevil was much more susceptible to all the extracts 
than maize weevil, having recorded the height mortality rate. 
 
Key words: Bean weevil, maize weevil, Lantana camara, African nutmeg, Enuopiri, mortality. 

 
INTRODUCTION 

 
Corn, Zea mays L., is a cereal grass related to wheat, 

rice, oat and barley; ranking second after wheat in order 
of world grain. This plant is regarded as versatile and has 
many uses since it can thrive in diverse climates; hence, 
it is grown in many countries. Aside from being one of the 
major sources of food for both human and animals, it is 
also processed into various food and industrial products 
including starches, sweeteners, oil, beverages, industrial 
alcohol and fuel ethanol. Moreover, thousands of foods 
and other everyday items such as toothpaste, cosmetics, 
adhesives, shoe polish, ceramics, explosives, 
construction materials, metal molds, paints, paper goods 
and textiles contain -corn components. In addition, corn 
products are rapidly replacing petroleum in many 
industrial applications. Polylactide (PLA), a biodegradable 
polymer made from corn is being used successfully in the  
 
 
 
*Corresponding author. E-mail: oluwasinagbenga@yahoo.com. 

 
 
 

 
manufacture of a wide variety of everyday items such as 
clothing, packaging, carpeting, recreational equipment 
and food utensils of renewable resource (Garcia, 1990).  

Cowpea (Vigna unguiculata (L.) Walp.) is one of the 
most widely adapted, versatile, and nutritious grain 
legumes (Ehlers and Halla, 1997). It had been consumed 
by humans since the earliest practice of agriculture in 
developing countries of Africa, Asia and Latin America, 
where it is especially valuable as a source of dietary 
proteins as well as vitamins and minerals (Singh et al., 
2003). Though substantial quantities of cowpeas are 
produced, before harvest or during storage the seeds are 
vulnerable to infestation by many insect pests, 
constituting the major constraint on the food availability. 
Over 90% of the insect damage to cowpea seeds is 
caused by the “cowpea weevil” Callosobruchus 
maculatus F. (Coeloptera: Bruchidae), a pest to several 
pulses including chickpeas (Cicer arietinum L.), lentils 
(Lens culinars Medik.), soybeans (Glycine max Mer.) and 
common beans (Phaseolusvulgaris L.). Indeed C. maculatus 



 
 
 

 

infestation on stored legumes may reach 50% within 3 to 
4 months of storage (Pascual-Villalobos and Ballesta-
Acosta, 2003). Maize weevil (Sitophilus zeamais 
Motschulsky), may infest the corn grain during storage 
and transport, attack may start in the mature crop when 
the moisture content (MC) of the grain had fallen to 18 to 
20%. Subsequent infestations in store result from the 
transfer of infested grain into store or from the pest flying 
into storage facilities, probably attracted by the odor of 
the stored grain. In stored maize, heavy infestation of this 
pest may cause weight losses of as much as 30 to 40%, 
although losses are commonly 4 to 5% (Casey, 1994). 

The chewing damage caused by the weevil (bean and 
maize), brings about increased respiration in the seeds 
(hot spots), which promotes evolution of heat and 
moisture and in turn provides favorable living condition for 
molds leading to production of aflatoxin. Subsequently, at 
very high moisture levels, bacterial growth is favored 
which ultimately gives rise to depreciation and finally total 
loss (Dahiya, 1999).  

Controlling stored pests is not an easy job although 
synthetic chemicals are available for use. Effective pest 
control is no longer a matter of heavy application of 
pesticides (because many rural area farmers resulted to 
the use of large quantity insecticides because of lack of 
application knowledge), partly because of rising cost of 
petroleum – derived products but largely because 
excessive use of pesticide promotes faster evolution of 
resistant form of pests, destroys natural enemies, turns 
formerly innocuous species into pests, harms other non-
target species and contaminates food (Busungu and 
Mushobozy, 1991). 

There is, thus, an urgent need for control agents, 
which are less toxic to man and more readily degradable. 
Among which is the use of botanical pesticides with low 
mammalian toxicity and can effectively prevent and/or 
suppress insect pests especially in storage (Golob and 
Webley, 1980) . It had been well reported that extracts 
from a variety of plants have potent insect pest-control 
properties, and they have being found to affect the 
biology of target insects in different modes such as 
ovicides, repellents, antifeedants, fumigants and contact 
toxicants, and insecticides (Watanabe et al., 1993; 
Hough-Goldstein, 1990; Karr and Coats, 1988; Rice and 
Coats, 1994; Tsao et al., 1995) . Recently, herbal extracts 
that are not harmful to the environment, have been 
shown to be effective natural preservatives (Grafius and 
Hayden, 1998; Sen, 2001). In addition, plant- based 
pesticides are renewable in nature and cheaper. Also, 
some plants have more than one chemical as an active 
principle responsible for their biological properties. These 
may be either for one particular biological effect or they 
may have diverse ecological effects. The chances of 
developing quick resistance to different chemicals are 
highly unlikely (Saxena et al., 1989). Plant-derived 
pesticides can be transferred into practical applications in 
natural crop protection, which can help the small-scale 

 
 
 
 

 

farmers (Binggeli, 1999). Three locally available plants, 
Lantana camara (Verbenaceae), African nutmeg 
[Monodora myristica (Gaerth) Dunal] and Enuopiri 
[Euphorbia lateriflora, Schum and Thonner] were 

evaluated to determine their nature as grain protectants 
against Sitophilus zeamais and C. maculatus (F.). 

 
MATERIALS AND METHODS 
 
This study focused on the effectiveness of hexane extracts of 
Enuopiri stems, L. camara leaves and the seeds of African nutmeg 
as protectants of stored maize and bean grains against attack by S. 
zeamais and C. maculatus (F.). Effectivity was based on the adult 
mortality tests under laboratory conditions. The experiment was 
conducted at the laboratory of Chemistry Department Federal 
University of Technology, Akure, Ondo State, Nigeria, from August 
2006 to November 2006. 

 
Collection and preparation of test materials 
 
Fresh and matured leaves of L. camara (from police headquarter 
Akure) were gathered and brought immediately to the laboratory 
and stems of Enuopiri (Euphorbia lateriflora Shum and Thonner) 
were obtained from Anu-Olu Hospital, Ilobu, Osun, State), while 
African nutmeg seeds [Monodora myristica (Gaerth) Dunal] were 
bought at Akure Main Market (Oja Oba). Mr. Solomon O. Aduloju of 
Department of Crop Soil and Pest Management, FUTA, 
authenticates these materials. The leaves and the stem materials 
were air dried in the laboratory until crispy and African nutmeg 
seeds were dehulled. The materials were pulverized using a 
laboratory blender and sieve to obtain uniform particle size. The 
resulting powders were kept separately in glass containers with 
screw capa and stored at room temperature prior to use. 300 g of 
each of the materials were then exhaustively extracted with n-
hexane using a soxhlet apparatus. These extracts were 
concentrated and kept separately in different labelled bottle 
containers and stored in a refrigerator. 

 
Mass rearing of weevil 
 
Adult maize weevil (S. zeamais Motschulsky) and bean weevil [C. 
maculatus (F.)] were isolated respectively from already infested 
maize grains (Z. mays) and cowpea [V. unguicalata (L.) Walpa] 
obtained from the Research Laboratory of the Department of Crop, 
Soil and Pest Management, FUTA, Ondo State, Nigeria. Materials 
such as corn seeds and cowpea used to culture the weevil were 
thoroughly cleaned and exposed in an oven to ensure the absence 
of insects, mites or disease-causing microorganisms. The treated 
corn seeds and cowpea seeds were then respectively put inside 
rubber containers previously washed, sterilized and dried. Into the 
containers containing corn seeds were added isolated maize weevil 
and to the container containing cowpea seeds were added bean 
weevil, respectively, from maize and bean weevil obtained from 
infested maize and bean grains. The plastic containers were 
covered with a net fastened tightly with rubber bands. The rearing 
of the insects was done in the laboratory to adapt them to the 
laboratory condition. The rearing was given enough time until new 
adult insects emerged; these were then used for the experiment. 

 

Adult mortality test 
 
Five different test concentrations (w/v of extract /hexane) were 

prepared: 10, 7.5, 5, 2.5 and 1 all in g/100 ml respectively. 0.5 ml 



  
 
 

 
Table 1. Percentage yield of the extracts.  

 
Plant Solvent Mass of extracts obtained (g) % yield of extracts 

 

African nutmeg 
Hexane 

58.35 19.45 
 

Lantana camara 39.45 13.15 
 

 
 

Enu opiri  43.52 14.51 
 

 
 
 
 
prepared solution of varying concentration was applied inside 
different Petri-dishes that had been previously washed, sterilized 
and dried, while 0.5 ml hexane (without the extract) was poured 
inside separate Petri-dishes as control. All the Petri-dishes were left 
overnight for the solvent used for preparing the solution to 
evaporate before introducing the weevil. After 24 h, 10 untreated 
(uninfested) cowpea and corn seeds were respectively placed in the 
centre of different Petri-dishes, (including the control). Ten active 
adult bean weevil (C. maculatus) and maize weevil (S. zeamais 
Motschulsky) were placed in each of the Petri-dishes containing the 
cowpea and maize seeds, respectively. To the control Petri-dishes 
were also added ten active adult bean weevil (C. maculatus) and 
maize weevil (S. zeamais Motschulsky), respectively. The Petri-
dishes were then loosely covered to allow passage of air. Weevil 
mortality was assessed and recorded after 1, 6, 12, 18 and 24 h. 
The experiment was carried out in triplicate. Percent adult mortality 
was determined by counting the number of dead insects divided by 
the total number of insects introduced multiplied by 100, (Lajide and 
Escoubas, 1990] 
 

 
Statistical analysis 
 
The data obtained were analysed by Probit analysis using Duncan’s 

multiple range test (DMRT) and analysis of variance (ANOVA), 

while regression analysis model was used for the computation of 

LD50 and LD90 
 

 

RESULTS 

 

The result of the percentage extract yields was presented 
in Table 1 below. African nutmeg hexane extract had the 
highest yield followed by Enu-opiri and L. camara 
respectively.  

Table 2 presented the result of the percentage insect 
mortality of the extracts on bean weevil. Significant 
treatment effects were observed with the number of the 
dead insects after the treatment duration. Table 3 shows 
the lethal dose analysis of the percentage insect 
mortality. The result collaborated the effectiveness and 
the economic valuability of African nutmeg above other 
extracts  

Table 4 presents the result of percentage insect 
mortality of extracts on maize weevil. The result showed 
that among the botanical extracts used, African nutmeg 
had the highest insect mortality and Enu-opiri had the 
lowest, after 24 h treatment. Table 5 presents the lethal 
dose activity of the extract, indicating that African nutmeg 
was superior protectant among all the extract, with small 
quantity of its extract achieving highest insect mortality 

 
 
 
 
DISCUSSION 

 

The result of the percentage extract yields from the 
various plants as presented in Table 1 showed that 
African nutmeg hexane- extract had the highest yield of 
19.45%, while L. camara had 13.15% and Enuopiri had  
14.51% yield. Thus African nutmeg had 4.91 and 6.30% 
yield higher than Enu-opiri and L. camara extracts, 

respectively. Enu-opiri had 1.36% extract yield higher 
than Lantana camara, which had the lowest extract yield 
among all the extract:  

Extract Yield (%)  mass of extract obtained x100 

% mass of sample 
 
 
 
The result of the percentage insect mortality of the 
extracts on bean weevil as presented in Table 2 indicated 
that African nutmeg hexane extract had superior 
effectiveness among all the botanical extracts. Having 
76.70% insect mortality with 1 g/ 100 ml of extract 
treatment after 24 h, while L. camara had 20.00% and 
Enu-opiri had 6.7%. The effectives of African nutmeg 
above other extracts were confirmed after treatment at 
various hour(s). African nutmeg extract was able to 
record 100% insect mortality with 10 g/100 ml of its 
extract at 1, 6, 12, 18 and 24 h of insect treatment, while 
L. camara had 93.3% and Enu-opirih had 46.70% all with 
10 g/ 100 ml, only after 24 h of treatment. The result from 
Table 3 showed that it would be economical to embark on 
mass production of African nutmeg hexane extract for 
use as protectant of grains, because small quantity of .65 

g/ 100 ml (LD50) was able to achieve 50% insect mortality 

and 2.4 g/100 ml (LD90) was able to kill 90% of the insect 

within 24 h of the treatment, as against the use of 5.30 g/ 

100 ml (LD50) and 9.51 g/100 ml (LD 90) for L. camara  
extract, while Enu-opiri (LD50) and (LD90) was 

undetectable within the test period and with the extract 
mass used.The result of percentage insect mortality of 
the extracts against maize weevil presented in Table 4 
showed that insect mortality increased with increase in 
the mass of the extract used and treatment duration, 
though none of the extract was able to achieve 100% 
mortality after 24 h treatment. African nutmeg still had the 
highest mortality of 96.70% after 24 h treatment with 10 
g/ 100 ml extract, L. camara had 73.3% and Enu-opiri 
had 50.00%.  

Table 5 presented lethal dose result of the plant extracts. 



 
 
 

 
Table 2. Percentage mortality of hexane extracts on bean weevil.  

 
 

Plant Extract 
Conc  Exposure duration (h)  

 

 
(g/ 100 ml) 1 6 12 18 24  

   
 

   1 20.0±0.0
b
 33.3±3.3

b
 50.0±5.8

b
 66.7±3.3

b
 76.7±3.3

b
 

 

   2.5 36.7±3.3
c
 46.7±6.7

c
 60.0±5.8

b
 73.3±3.3

c
 90.0±5.8

c
 

 

 A. nutmeg Hexane 5 53.3±3.3
d
 70.0±5.8

d
 86.7±6.7

c
 93.3±3.3

d
 100.0±0.0

d
 

 

   7.5 73.3±3.3
e
 86.7±6.7

e
 93.3±3.3

c,d
 100.0±0.0

d
 100.0±0.0

d
 

 

   10 100.0±0.0
f
 100.0±0.0

f
 100.0±0.0

d
 100.0±0.0

d
 100.0±0.0

d
 

 

   1 3.3±3.3
a
 6.7±3.3

a,b
 13.3±3.3

b
 16.7±3.3

b
 20.0±0.0

b
 

 

   2.5 10.0±0.0
b
 13.3±3.3

b,c
 20.0±0.0

b
 26.7±3.3

c
 26.7±3.3

b
 

 

 L. camara Hexane 5 16.7±3.3
b
 23.3±3.3

c,d
 33.3±3.3

c
 40.0±0.0

d
 46.7±3.3

c
 

 

   7.5 16.7±3.3
b
 30.0±5.8

d
 43.3±3.3

d
 53.3±3.3

e
 60.0±5.8

d
 

 

   10 30.0±0.0
c
 43.3±3.3

e
 56.7±3.3

e
 66.7±3.3

f
 93.3±3.3

e
 

 

   1 0.0±0.0
a
 0.0±0.0

a
 0.0±0.0

a
 3.3±3.3

a,b
 6.7±3.3

a,b
 

 

   2.5 0.0±0.0
a
 3.3±3.3

a
 6.7±3.3

a,b
 10.0±0.0

b
 10.0±0.0

b
 

 

 E. opiri Hexane 5 6.7±3.3
a,b

 13.3±3.3
b
 16.7±3.3

b,c
 20.0±0.0

c
 26.7±3.3

c
 

 

   7.5 10.0±5.8
b
 16.7±3.3

b
 23.3±3.3

c,d
 33.3±3.3

d
 40.0±0.0

d
 

 

   10 13.3±3.3
b
 26.7±3.3

c
 33.3±3.3

d
 40.0±0.0

d
 46.7±3.3

e
 

 

 Control  0 0.0±0.0
a
 0.0±0.0

a
 0.0±0.0

a
 0.0±0.0

a
 0.0±0.0

a
 

 

 
Values are means of three replicate ± Standard error. Column means followed by different letters are significantly different at P < 0.05. 
A.nutmeg represents African nutmeg, E.opiri represents Enu opiri. 

 
 

 
Table 3. The LD50 (g/ 100 ml) and LD90 (g/ 100 ml) of extracts on Bean Weevil.  

 

Duration (h) 
African nutmeg L. camara  Enuopiri 

 

Hexane LD50 Extract LD90 Hexane LD50 Extract LD90 Hexane LD50 Extract LD90  

 
 

12 0.74 6.74 9.08    
 

18 0.71 4.39 6.01    
 

24 0.65 2.49 5.30 9.51   
  

Represents cases where LD can not be calculated from result. 
 
 

 

African nutmeg is the best extract for mass production, 
since it was able to achieve 50 and 90% insect mortality 

with the least extract mass of 1.48 g/100 ml (LD50) and 
8.97 g/100 ml among all the extracts, against 6.96 g/ 100 

ml (LD50) for L. camara and 9.62 g/100 ml (LD50) for Enu-

opiri. The LD90 of L. camara and Enu-opiri was 
undetectable  

In conclusion, results of the study revealed that all 
tested plant extracts exhibited mortality action against 
maize weevil and bean weevil, with bean weevil been the 
most susceptible to the plant extracts. African nutmeg 
hexane extract had 100% bean weevil insect mortality 
with 5 g/ 100 ml after 24 h of treatment, whereas 73.3% 
mortality was recorded for maize weevil. With 10 g/ 100 
ml extract mass applied after 24 h African nutmeg, L. 
camara and Enu-opiri respectively were able to record 

 
 
 

 

100, 9.30 and 46.7% for bean weevil, but had 96.7, 73.3 
and 50% respectively for maize weevil. 

The efficacies of different treatments varied, depending 
on the source of the active ingredient. Lantadene A, 
Lantadene B and high flavonoid content, which is mostly 
associated with deterrence against insects are present in 
L. camara (Ghisalberti, 2000), African nutmeg contained 

among other charicol, thymol, a – pinene and myristicin a 
poisonous constituent (Dales, 1996; Cobley, 1976) and 
Enuopiri contained high quantity of secondary 
metabolites (Segler, 1994). This result finds support from 
other studies in which plant extracts were effective in 
controlling bean weevil and maize weevil, and that they 
have been effectively used as stored product protectant 
against insect pests (Bunner, 1993; Ofuya et al., 1992; 
Aku et al., 1998; Singh et al., 1978; Pandey et al., 1981 



  
 
 

 
Table 4. Percentage mortality hexane extracts on maize weevils.  

 
 

Plant Extract 
Conc  Exposure duration (h)  

 

 
(g/ 100 ml) 1 6 12 18 24  

   
 

   1 16.7±3.3
a,b

 26.7±3.3
b
 3 3.3±3.3

b
 46.7±3.3

b
 46.7±3.3

b
 

 

   2.5 26.7±3.3
b
 36.7±3.3

b,c
 43.3±3.3

b,c
 53.3±3.3

b,c
 56.7±3.3

b
 

 

 A. nutmeg Hexane 5 43.3±8.8
c
 43.3±3.3

c
 53.3±3.3

c
 63.3±3.3

c,d
 73.3±6.7

c
 

 

   7.5 53.3±8.8
c
 56.7±3.3

d
 6 6.7±3.3

d
 73.3±6.7

d
 76.7±8.8

c
 

 

   10 60.0±5.8
c
 70.0±0.0

e
 83.3±8.8

e
 90.0±5.8

e
 9 6.7±3.3

d
 

 

   1 3.3±3.3
a
 6.7±3.3

a,b
 10.0±0.0

b
 10.0±0.0

b
 10.0±0.0

b
 

 

   2.5 3.3±3.3
a
 13.3±3.3

b,c
 16.7±3.3

b
 20.0±0.0

c
 20.0±0.0

c
 

 

 L. camara Hexane 5 1 3.3±3.3
b
 20.0±0.0

c,d
 30.0±0.0

c
 36.7±3.3

d
 40.0±0.0

d
 

 

   7.5 16.7±3.3
b
 26.7±3.3

d
 33.3±3.3

c
 43.3±3.3

d
 53.3±3.3

e
 

 

   10 2 6.7±3.3
c
 40.0±5.8

e
 53.3±3.3

d
 63.3±3.3

e
 73.3±3.3

f
 

 

   1 0.0±0.0
a
 3.3±3.3

a
 6.7±3.3

a
 10.0±0.0

b
 10.0±0.0

b
 

 

   2.5 3.3±3.3
a
 10.0±0.0

a
 16.7±3.3

b
 16.7±3.3

c
 20.0±0.0

c
 

 

 E.opiri Hexane 5 16.7±3.3
b
 23.3±3.3

b
 23.3±3.3

b
 23.3±3.3

d
 30.0±0.0

d
 

 

   7.5 16.7±3.3
b
 26.7±3.3

b
 33.3±3.3

c
 33.3±3.3

e
 36.7±3.3

e
 

 

   10 20.0±5.8
b
 30.0±5.8

b
 36.7±3.3

c
 40.0±0.0

f
 50.0±0.0

f
 

 

  Control 0 0.0±0.0
a
 0.0±0.0

a
 0.0±0.0

a
 0.0±0.0

a
 0.0±0.0

a
 

 

 
Values are means of three replicate  Standard error. Column means followed by different letters are significantly different at P < 0.05. 
A.nutmeg represents African nutmeg, E.opiri represents Enu-opiri. 

 

 
Table 5. The LD50 (g/100 ml) and LD90 (g/ 100 ml) of extracts on maize weevil.  

 
 

Duration (h) 
African nutmeg L. camara Enu Opiri 

 

 
Hexane LD50 Extract LD90 Hexane LD50 Extract LD 90 Hexane LD50 Extract LD90  

  
 

 12 4.09  9.75    
 

 18 1.78 9.60 8.02    
 

 24 1.48 8.97 6.96  9.62  
 

 
 Represents cases where LD can not be calculated from results.

 

 

Therefore, the results findings revealed that African 
nutmeg, L. camara and Enuopiri hexane extracts could 
be used as protectant against maize weevil, S. zeamais 
Motsch and bean weevil, C. maculatus (F.). It is 
recommended therefore that a similar study be conducted 
by using separately the other parts of the test plants like 
roots, flowers or even the whole plant to further evaluate 
their efficacy against maize weevil, bean weevil and other 
important stored product pests. In addition, the use of 
other solvent to extract those plants is also recommended 
to further determine their potential as insecticide against 
storage seed pests 
 

 
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