INTRODUCTION
Cucumber (Cucumis sativus L.) is a member of the family Cucurbitaceae (gourd family).The crop is thought to have
originated in India and some other parts of Western Asia. Cucumber is an annual,
warm season, dioecious, creeping or trailing
herbaceous vine that grows on trellises or other supports, wrapping around them
with thin, spiral tendrils. The stem is stout, simple four- angled and bears
large triangular or ovate shaped leaves that form a canopy over the fruits. The
fruit of cucumber is roughly elongated with tapeted
end (Trebick et al., 2015). The fruits are
eaten raw or prepared as salad and pickle while the young leaves are eaten as
vegetables or salad particularly in Malaysia and Indonesia (Ojiewo
et al., 2015). Cucurbits in general are a family of healthy foods and
cucumbers in particular are a prime dieting food being low in calories. One
hundred
grammes of the fresh fruit of the crop is reported to
contain about 96 percent water, a little fibre, a few
calories, providing a good source of vitamins A, K and C and a large amount of
potassium (Ojiewo et al., 2015). Its high
moisture content contributes to its diuretic activity and cleansing action
within the body by removing accumulated pockets of metabolic waste materials,
chemical toxins especially uric acid and xenobiotics.
Hence, Cucumbers could be beneficial for those who are burdened with arthritis.
The fruit rind contains high levels of cucurbitacins,
which antagonize cancer preventing their proliferation and survival. The rind also has been found to help with
symptoms of diabetes since cucurbitacins
in cucumber
stimulate insulin release and regulate the metabolism of a key
hormone in the processing of blood sugar, hepatic glycogen (Ojiewo
et al., 2015).
However, production of this important crop is strongly
constrained by attacks of insect pests which decimate the above ground
structures of the plant especially in humid tropical locations. Major insect
pests associated with the crop include cucumber beetles, red pumpkin beetles,
fruit flies, squash bugs, aphids, whiteflies, squash vine borers and two-spotted
spider mites. Losses due to attacks of these insects may reach up to 35–75% at
the seedling stage or total crop failure (100%) in severe infestations of the
field (Khan et al., 2012). Control of these insect pests so far is
largely achieved by synthetic chemical treatments such as Cypermethrin, acetamiprid, bifenthrin or malathion.
In the view of many workers, overuse and/or misappropriation of these
interventions are harzadous to both environmental and mammalian
health (Jallow et al., 2017). Owing to these, several
researchers in recent years have reported the insecticidal activity of tropical
higher plants (Asawalam, 2006).
Asawalam
(2006) reported that extracts derived from Piper guineense
effectively checked the ravages of Sitophilus
zeamais on stored maize grains whereas Oparaeke (2007) noted that powder from the same plant
substantially reduced the populations and attacks of
Maruca
sp. and Clavigralla sp. on cowpea in
the field. The use of extracts of the fish poison bean (Tephrosia
vogelii) as plant-derived insecticide for
veterinary and conventional crop production in Tanzania, Uganda and other
countries in East Africa has been reported (Denza
et al., 2007). Recently, researchers in Western Nigeria found that extracts
of
T. vogelii reduced the population of Phyllotreta coniferea,
D. undecimuctata, Bactrocera
curcubitae, Zonocerus variegatus and Podagrica
spp. on treated roselle (Hibiscus sadbarilla L.) (Zobo plant) and water melon (Olaniran
and Adebayo, 2013; Olaitan and Adebayo, 2015).
However, evaluations of the insecticidal efficacy of extracts of the plant
against the major insect pests of the crop in Umudike
Southeastern Nigeria are scarcely available.
Therefore, this work is tailored to assess the efficacy of
extract of T. vogelii for the control of major
insect pests of cucumber in Umudike Southeastern
Nigeria, and to evaluate the impacts of the treatments on the yield and yield
components of the treated crop.
MATERIALS AND METHODS
Experimental site
The study was conducted from March - May 2018 cropping season at the Michael Okpara University of Agriculture Western Farm Umudike, which is located on the latitude 50 291N
and longitude 70 331E with average annual rainfall of
2177mm and temperature of 290C-310C with relative humidity
of 50-90 in the rain-forest ecological zone of Southeastern Nigeria (NRCRI,
2016).
Source of seeds and
Field Preparation
The seeds of Cucumber
(Var: Poinsette) (Fig. 1)
obtained from the Research and Training (R&T) Unit of the College of Crop and
Soil Sciences of Michael Okpara University of
Agriculture Umudike (MOUAU) were used for the study.
The Research field was ploughed, tilled and ridged manually using hoe that made
for easy breakage of the soil lumps to enable proper establishment of the crop.
Five tonnes per hectare (5 tonnes/ha) of poultry manure was incorporated into
the ridges during preparation (Enujeke, 2013; Agu et al., 2015). The seeds were sown three per hole
at a spacing of 60 cm ×
50cm on the two sides of the ridges and later thinned to one seedling after
emergence to achieve one plant per stand. Each experimental plot measured 2m × 2.5m and consisted of four rows of ridges. The
experiment was laid out in a Randomized Complete Block Design (RCBD) with four
replications. The whole field was weeded at fortnightly intervals (Enujeke,
2013;
Agu et al., 2015).
In terms of the mean fruit yield from the test cucumber
crop, results obtained from the study are presented in Fig. 3. The results
showed that the plots treated with Cypermethrin
which recorded 12,000 (kg/ha) significantly (P<0.05) gave the highest fruit
yield per hectare while the control (untreated) plots gave the lowest fruit
yield (3000 kg/ha). This was because the treatments effectively reduced the
incidence (mean insect population) and attacks (severity) of the insect pests on
the treated crop. However there was no significant difference in fruit yield per
hectare in the plots treated with synthetic insecticides and plant extract.
Figure
3: Fruit yield (kg) per hectare of the treated cucumber plants in the field
DISCUSSION
Generally, findings in this study showed that irrespective
of time of observation and collection of data, the mean insect population on the
control (untreated) experimental plots had the highest (P≤0.05) number of insect
pests attack compared to those treated with the synthetic insecticides and
extract of T. vogelii. It also depicted that
the plots treated with Cypermethrin
(synthetic) recorded the highest mortality of the test pest species, followed by
those treated with extracts of T. vogelii
which effectively and substantially controlled the insect pests of cucumber.
Extracts of spice and other medicinal higher plants have
been reported to exhibit appreciable levels of insect killing activities (Amuji et al., 2012). Many workers have reported that
extracts of T. vogelii exhibited strong
insecticidal activity against several insect pests of agricultural crops
(Adebayo 2003; Babarinde et al., 2001). According to Koona and Dorn
(2005), powdered hexane extracts of dried leaves of T. vogelii effectively protected legumes seeds in storage
against attacks from bruchids and reduced the damage
caused by Callosobrunchus
maculatus. C. chinensis and
Acanthoscelides
obstectus on the treated seeds by 7.1% compared
with 99.8% recorded on grains in the control experiment. Similarly, a
dose-dependent percentage reduction of 45-64 on populations of P. coniferea, D. undecimpucteta
and
B. curcubitacae on treated water melon has been
reported. Also in another field trial, Olaniran and
Adebayo (2013) reported that up to 51-80% reduction of populations of Z. variegatus and Podagrica
spp. on roselle (Zobo
plant) treated with extracts of T. vogelii.
Findings in this study where the mean population of the three assayed
insect pests were effectively reduced and statistically (P<0.05) high numbers of
these cucumber decimating insects killed by the extracts are in conformity with
the reports of the various workers above.
In this study also, statistically (P<0.05) higher yield
(8000-12000 kg/ha) and yield parameters were recorded on the treated cucumber
crop compared to plants in the control group (3000 kg/ha). These are in strong
agreement with the reports of Olaniran and Adebayo
(2013) who found that treatment of roselle (Zobo plant) with extracts of T. vogelii and Azadirachta
indica either singly or in combination; in
addition to reducing the populations of Podagrica spp and Z. variegatus significantly increased the yield from the
treated crop. Secondary metabolites
of tropical higher plants are reported as their arsenal against pests and
pathogens (Enyiukwu et al., 2014). The ability
of T. vogelii extract to stem the population
and attacks of the assayed insect pests and consequently increased the mean
fruit yield of the treated cucumber may have been due to its rich content of
water soluble secondary metabolites such as rotenone,
rotenolone,
rotenoids such as tephrosin
and deguelin or some solvent soluble fatty acids
reported to possess insecticidal attributes (Denza
et al., 2009; Enyiukwu et al., 2016; and Chukwu, 2018).
However, the low mean yield recorded on the plants in the
untreated control plots could be attributed to the attacks from high levels of
the populations of the 3 insect pest species on the treated cucumber which
led to increased loss of foliage, larger disruption of
meristematic
areas and/or translocation of products of photosynthesis of the affected plants
thereby leading to inhibition of rapid cell multiplication, reducing
photosynthesis and energy formation (Eifedeyi and Remison, 2010).
With the
exception of Cypermethrin, all the synthetic
treatments used in this study are pyrethroids and neo-nicotinoids known to be easily degraded when exposed to heat
and UV-light (Brown, 2006, Enyiukwu et al.,
2014). Therefore the higher percentage mortality of the insect pests’
populations and consequently higher significant fruit yield recorded on plots
treated with cypermethrin compared to those exposed to
the extract of T. vogelii and the synthetic
copies of pyrethrin and nicotine may have been
informed by the longer persistence of cypermethrin on
the treated cucumber crop and the environment than the other treatments.
CONCLUSION
In conclusion therefore, leaf extract of T. vogelii could be used as an effective plant-derived
pesticide for controlling the insect pests of cucumber (C. sativus L.) for increased production of the crop in low
input agricultural systems of sub-Saharan Africa.
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