A Prescreen of Termicitidal Potentials of Aerial Parts of Castor, Ricinus communis, (Euphorbiaceae)
Preliminary investigations were carried out on the termiticidal
potentials of aqueous extract of the leaf, fruit and bark of castor, Ricinus
communis (Euphorbiaceae), on mortality and repellency of Macrotermes
natalensis in the laboratory towards the development of alternative
to synthetic termiticides. Ability of Nasutitermes species to rebuild
broken termatarium treated with leaf and fruit extract was also investigated
on the field. Results obtained show that the extracts had significant
(p<0.05) effect on the test parameters. Symptomlogical response of
M. natalensis to the extract included back lying of the insects
prior to their death with overall reduced excitability. Highest response
was observed in fruit extract. At 3 h after treatment (HAT), leave extract
caused significant mortality. Between 6-12 HAT, mortality due to different
extracts was not significant. However, at 24 HAT, mortality (82.00%) due
to fruit extract was significantly higher than mortality due to other
extracts. Also, fruit extract exerted highest repellency (90%) to M.
natalensis, which was followed by 87.27% repellency due to leaf extract,
both being class V repellency. The repellency due to bark (40%, class
II) was significantly the lowest. On the field, both leaf and fruit extracts
inactivated Nasutitermes species from rebuilding broken termatarium,
whereas untreated control was rebuilt within 24 h.
Termites (Isoptera:Termitidae) are agricultural pests in the tropical
and subtropical regions of the world. Their affinity for cellulose materials
make them deleterious to many plant species including timber, arable crops,
stored products and structural materials (Logan and El-Bakri, 1990; Stoll,
2000; Umeh, 2003). In Nigeria, different species have been reported on
various crops with Macrotermes on maize stem, cassava cuttings
and yam tuber sets (Umeh and Ivbijaro, 2003) and Nasutitermes on
citrus (Umeh, 2003). The first researcher of this study also encountered
Nasutitermes on susceptible yam (Dioscorea) species
at harvesting on termite-prone plots in Southwestern Nigeria.
Due to the economic importance of termites, several control strategies
have been employed all over the world. Control measures in Florida include
removal of remnant wood from the orchard soil and protection of vulnerable
crown by soil removal and application of insecticide to the base of citrus
tree (Stansly et al., 1992) and use of insecticidal baits (Stansly
et al., 2001). In Nigeria and certain West African countries, indigenous
methods of burning goat viscera, spreading of dry cell battery powdered
material, introduction of ants and use of wood ash were reported to be
non-effective. The most popular method has been use of synthetic insecticides
with organochlorines being the commonest product used in Mali, Burkina
Faso, Niger and Nigeria (Umeh, 2003). If the necessary precautions are
taken, the method is practically effective when the pest status approaches
economic damage level. Their disadvantages however include residual toxicity
and health hazard to humans and non-target species (Bouguerra, 1990).
Castor, Ricinus communis, is commonly found on refuse dumps near
house steads in many rural settlements in Southwestern Nigeria. Although
its insecticidal properties have been documented against stored product
pests (Okonkwo and Okoye, 1992) much has not been done on termiticidal
potentials of its aerial parts. In certain part of India, farmers usually
cultivate castor on plots to reduce termite infestation during the next
cropping season. The control effect has particularly been attributed to
root exudates (Stoll, 2000). The objective of this study was therefore
to carry out a preliminary investigation of termiticidal properties of
aerial parts of R. communis; thereby elucidate the necessity of
further studies towards incorporating it into Integrated Pest Management
(IPM) of termites in the cropping system of resource-poor farmers in developing
MATERIALS AND METHODS
M. natelensis used for laboratory bioassay was collected from
termateria within the campus of Ladoke Akintola University of Technology
(LAUTECH), Ogbomoso, Nigeria. The Nasutitermes termataria used
for field evaluation were also found within the campus. The experiment
was conducted in September 2006. Identification of the two species was
done at the Insect Collection Museum of the Department of Crop Protection
and Environment Biology, University of Ibadan, Ibadan, Nigeria.
Three parts (fresh leaves, bark and immature fruits) of red coloured
variety of R. communis used for the experiment were obtained from
LAUTECH Farms and the premises of Soun Stadium, Ogbomoso. Two kilograms
leaf, bark and fruit were separately pounded using mortal and pestle with
3 L of water and allowed to stand for 35 h for chemical reaction to take
place. The extract was thereafter decanted and was sieved to obtain a
stock solution. The stock solution was stored in plastic jars until when
needed for laboratory and field evaluation within 5 days post preparation
of the extracts.
Toxicity of R. communis to M. natalensis
Ten milliliters of each extract was pippeted on 1.5 g tissue paper
inside a 9 cm diameter Petri dish. The tissue paper (Product of John Browns
Nigeria Ltd., Apake, Ogbomoso) was folded to perfectly fit into the Petri
dish bottom. The stock solution was thoroughly stirred to ensure proper
mixture of the extract before it was pippeted. Ten M. natalensis were
introduced into Petri dish and was quickly covered to prevent insect`s
escape. There were three replicates. Mortality data were taken at 3, 6,
12 and 24 h after treatment (HAT).
Repellency of R. communis against M. natalensis
The method used for repellency bioassay was based on the area
preference test (McDonald et al., 1970) with some modifications.
Test arena consisted of 10x10x5 cm rectangular plastic bowls. Tissue paper
(0.5 g) was treated with 2 mL extract with the aid of a syringe. The control
was a tissue paper of similar weight treated with water. The two tissue
papers (treated and control) were put on opposite ends of a diagonal of
the rectangular plastic bowl. Ten M. natalensis were introduced
into the center of each repellency chamber. There were three replicates.
The numbers of insect present in the treated and untreated corners were
recorded after 20 min (Obeng-Ofori and Reichmuth, 1997). Percentage repellency
was calculated for each replicates according to the method of Sighamony
et al. (1986) as the difference between the numbers of insect on
treated corner and the control expressed as a percentage of the number
of insects introduced.
Effect of R. communis on Nasutitermes Ability to Rebuild
Bark extract was not used in this bioassay, based on the previous
laboratory bioassays that indicated its lowest potency. Six active termite
mounds (species of Nasutitermes were used, making three replicates
each of leaf and fruit extract. A portion (4 cm radius) of the termite
mound soil was removed and treated with 24 mL extract. Similar portion
of soil was broken as the control at the opposite side of the termite
mound to give 50 cm distance to the treated spot. The control was not
treated with extract. A broomstick was used to mark the treated arena.
At 24 h post treatment the setup was checked for possible remoulding of
the broken termite mound.
Mortality data were expressed as percentage of the total number of
insects introduced and corrected with Abbott`s formula (Abbott, 1925).
Data were arcsine transformed before analysis. It was later subjected
to two-way Analysis of Variance (ANOVA) and standard error of means were
calculated to show variations between replicates. Repellency data were
subjected to oneway ANOVA. For both sets of data, significant difference
between means were determined using Fischer`s Least Significant Differences
(LSD) at 5% level of probability, where differences existed. Repellency
was later classified according to McGovern et al. (1977);
class 0 = Negative repellency; class I = 0- 20%, class II = 20. 1-40%,
Class III = 40.1- 60%, class IV = 60.1-80%, class V = 80.1-100%.
Aqueous extracts of the aerial parts of R. communis were effective
against M. natalensis in the laboratory, although at varying
degrees. The symptomlogical response of the species to the three extracts
included back laying of the insect prior to their death with overall weakness
in excitability. The response was, however, more pronounced in fruit extracts
than in other two extracts. The result of analysis of variance indicated
that the efficacy of the extracts was affected by time after treatments.
Between 6-12 HAT, the efficacy of the three extracts was not significant
(p<0.05). However, at 24-HAT mortality due to fruit was significantly
(p<0.05) higher than mortality due to other treatments (Table
||Mean percentage mortality (Â±SE) of Macrotermes
natalensis exposed to Ricinus communis extract
|LSD = 10.19, SED = 5.08, Values are arcsine transformation
of original data, Means followed by the same letter(s) along the column
are not significantly different at 5% probability
||Mean percentage repellency of Ricinus communis
to Macrotermes natalensis
|Class II = 20.1-40%, class V = 80.1-100%, Means followed
by the same letter(s) along the column are not significantly different
at 5% probability
The result followed the same trend with what was obtained in toxicity
bioassay; with fruit extract exerting highest repellency (90%) to M.
natalensis (Table 2). This was directly followed
by leaf extract (87.27%). The repellency due to leaf and fruit were not
significantly different at 5% probability LSD, with the two values being
class V repellency. Repellency due to bark extract (40%) was significantly
the lowest and was of class II.
When the fruit and leaf extracts were experimented on their efficacy
to inactivate the ability of Nasutitermes to rebuild broken termatarium,
the two extracts had significant effects. It was discovered that the species
rebuilt the untreated broken termetaria arena within 24 h post treatment,
whereas the treated arena was not rebuilt. It was also observed that the
termites were migrating from the treated arena to the untreated parts,
while some even died at a short time post application of treatment.
In different part of the world particularly in India, China and Africa,
plant materials especially roots, twigs and flowers were collected from
the field or cultivated specially for the purpose of insect pest control
(Dales, 1996). The findings in this research reveal that R. communis
has termiticidal properties. Although, M. natalensis ingested
the extracts which could have caused stomach poison, the symptomlogical
response of the species to the extracts suggests that the mode of action
of the bioactive components was via nerve poison, in addition to oral
Fruit and leaf extracts were more effective than bark extract. This possibly
implies that the bioactive components of higher quality were in the leaves
and fruits than in the bark or that their form were more readily released
in fruits and leaves than when bark was used. Treas and Evans (1978) indicated
that different parts of the same plant species may have varying quantitative
or qualitative bioactive components. Duration of experiment also has significant
effects on mortality of M. natalensis. This confirms the finding
of Umeh and Ivbijaro (1998), Adedire and Lajide (1999) and Zhu et al.
(2003). The extended time of exposure killed higher percentage of
the species since they had no escape route in the experimental set up.
The result of repellency followed the same trend as that of mortality.
Although fruit (90.0%) repelled higher percentage than leave (87.27%),
there was no significant difference in their efficacy.
On the field, bark extract was not used because the two previous laboratory
biassays revealed its comparative poor performance as protectant against
M. natalensis. So, leaf and fruit extracts were screened to determine
their ability to inhibit Nasutitermes species from rebuilding broken
termatarium. The efficacy of the two extracts was established as some
insects migrated from the treated spot or died few minutes after treatments.
The finding on repellency test agrees with previous findings (Rahmon et
al., 1999; Lale and Alaga, 2001). With the present findings, the potential
of aerial parts of R. communis as termiticide at farmers` level
or around homestead is established. Fresh leaves and fruits displayed
greater effects than the bark.
The press cake of castor seed, although poisonous, is used as fertilizer
(Rehm and Espig, 1991; Stoll, 2000). Use of R. communis
as termiticide, therefore, has added advantages of serving as soil amendment.
Although, aspect of characterization and identification of active compounds
were not covered in this study, Treas and Evans (1978) listed alkaloid,
ricinine, cyanogenic glucoside, flavononoids, steroidal sapogenin, gallic
acid and potassium nitrate as bioactive component of castor leaf. Since
fresh leaf and fruits displayed greater termiticidal potentials than bark,
they may be exploited for local farmers` uses and further scientific studies.
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