Efficacy of Cymbopogon Schoenanthus L. Spreng (Poaceae) Extracts on
Diamondback Moth Damaging Cabbage
Yao Adjrah1*, Bakouma Laba2, Amen Y Nenonéné2, Koffi Koba2, Wiyao Poutouli3, Komlan Sanda2
1Laboratoire de Microbiologie et de Contrôle de qualité des Denrées Alimentaires, Ecole Supérieure des Techniques Biologiques et Alimentaires (ESTBA), Université de
Lomé BP 12281, Lomé - Togo
2Unité de recherche sur les Agroressources et la Santé Environnementale, Ecole Supérieure d’Agronomie, Université de Lomé, BP 20131, Lomé - Togo
3Laboratoire de Biologie Animale et de Zoologie, Faculté des Sciences, Université de Lomé, BP 1515, Lomé - Togo
*Corresponding author:
Yao Adjrah,
Laboratoire de Microbiologie et de
Contrôle de qualité des Denrées Alimentaires
Ecole, Supérieure des Techniques
Biologiques et Alimentaires (ESTBA) Université de Lomé BP 12281
"
Lomé-Togo, Tel: (228) 90 08 92 61 Fax: (228) 22 21 85 95 E mail: neladjrah@gmail.com
Received March 31, 2012; Accepted June 15, 2012; Published June 17, 2012
Citation: Adjrah Y, Laba B, Nenonéné AY, Koba K, Poutouli W, et al. (2012) Efficacy
of Cymbopogon Schoenanthus L. Spreng (Poaceae) Extracts on Diamondback
Moth Damaging Cabbage. J Biofertil Biopestici 3:119. doi:10.4172/2155-6202.1000119
This study aims to examine the insecticidal properties of the aerial part of Cymbopogon schoenanthus.
Cabbage plants were sprayed with the aqueous extracts of C. schoenanthus leaves as treatment, and the
damage levels of Plutella xylostella was assessed. In vitro, the emulsified essential oil concentrations were
used in a contact test on the larvae in order to assess the mortality effects. The larvae survival time was only 22
seconds with C. schoenanthus emulsified oil treatment (2 g/l), whilst it exceeded 44,100 seconds (over 12 hours)
for the dimethoate. The nutrition test showed that at 48 h period, a significant effectiveness against larvae was
observed with emulsified oil treatment 2 g/l (60% mortality) versus 10% of mortality for dimethoate. Cymbopogon
schoenanthus can validly be used as alternative in P. xylostella management. The results of the field experiments
showed no significant difference between the treatments and the control in terms of marketable cabbages
harvested.
Apart from being consumed as a current vegetable, cabbage has
been valued for medicinal purposes in treating headaches, gout, and
diarrhea, inflammatory and gastrointestinal disorders [1-4]. Some
researchers have focused their works on the capacity of cabbage to
reduce the risks of some cancers [5,6], especially due to the content of
glucosinolates and derived products, flavonoids and other phenolics
in cabbage [7-9]. The antioxidant activity of these compounds has
been shown to correlate with vitamin C and phenolic phytochemicals
content [4,6,10,11].
The intensified growing of cabbage has led to a common problem of
high pest infestation, which is caused mostly by the Diamondback Moth
(DBM) Plutella xylostella [12-14]. DBM larvae are very difficult pests to
control [15] and therefore, are the greatest threat to crucifer production
in many parts of the world. The losses can reach the 90% [13,16]. This
explains the large use of insecticides in crucifer production. Owing to
its polyvoltine characteristics and serious overlap of generations, this
pest can easily develop resistance to various kinds of insecticides [17-19], including biological one such as Bacillus thuringiensis [20-22], and
particularly in sub-tropical and tropical countries [23]. To overcome
resistance, farmers resort to increasing frequency and rates of pesticide
applications and to mixed cocktails of pesticides [16]. In addition, the
information about the chemical composition of these pesticides is not
always publicly available [24]. In Togo, vegetable producers currently
apply seven different chemical insecticides (fipronil, chlorpyrifos
ethyl, cypermethrin, dimethoate, endosulfan, Bacillus thurgensis and
acephate) on cabbage and in over 11 applications within 3 months
of crop growth prior to harvest. Indiscriminate use of pesticides
constitutes one of the main environmental and public health problems
in developing countries leading to harmful effects on the ecosystems,
the health of both farmers and consumers [25-29].
Biological options in an integrated pest management (IPM)
approach offer a solution to sustainable control of DBM. In West
Africa, farmers use botanical pesticides, such as plants extracts of Azadirachta indica A. Juss, Melia azedarach L. against DBM [30].
Cymbopogon schoenanthus is efficient in the biological control against
pests [31,32]. Cymbopogon schoenanthus L. Spreng. (Poaceae) or
lemon grass, originally from India, is a warm climate aromatic plant
that grows in Togo [31]. It’s essential oils are very rich in piperitone
[31,33,34] which is responsible for the insecticidal activity of this plant
[31,35]. This present work aims at using aqueous leaf extracts and
low concentrations of essential oil of C. schoenanthus as an integrated
management approach to the control populations of P. xylostella and
their larvae in vitro and the field.
Materials and Methods
Experimental site
Experiments were conducted from May 2009 to August 2010 at
Agricultural Teaching Experimental Station (ATES) of University of
Lomé (UL), Togo. Plant extractions, nutrition and contact tests on P.
xylostella were carried out respectively in Chemistry and Plant Biology
laboratories of the Ecole Supérieured’Agronomie (ESA) of UL.
Plant and materials
Cabbage cultivar “KK cross” purchased in a seeds shop in the
outskirts of Lomé was used for the assay. Leaves of C. schoenanthus were collected at the Agricultural Teaching Experiment Station of UL
where this plant was cultivated just for experimental purposes.
Source of insects
Fourth instars larvae of P. xylotella were collected in cabbage
growing field and from a small rearing unit of P. xylostella of ATES.
Chemical insecticide dimethoate was purchased from a local
supplier as ‘Calidim’ 400 EC (Caliope Chemical Industries Ltd, France).
P. xyllostella larvae control with emulsified oil of C.
schoenanthusin vitro
Contact tests: Ten fourth instars larvae were introduced into
a Petri dish, and were sprayed (using ULV apparatus) with the five
formulations: DW (Distilled water); THE1 (essential oil 2 g, hand
soap containing soda 2 g, distilled water 96 g); THE2 (essential oil 1
g, hand soap containing soda 2 g, distilled water 97 g); SW (hand soap
containing soda 2 g, distilled water 98 g); and DT (40 μl aqueous solution
containing 0.25 mg of active ingredient). The soap is an adjuvant used
to support oils on the leaf surface and during larvae contact. The test
was replicated four times with each formulation. Larval behavior was
observed with a magnifying glass, and a chronometer was used to
determine the duration of larval survival. The parameter measured was
mortality, and larvae were considered dead if they did not move either
their head or their thorax when touched.
Nutrition test: A randomized complete block design five
treatments each replicated 4 times was used. Fresh cabbage leaves
discs (diameter 5 cm) were sprayed with the formulations DW, THE1,
THE2, SW and DT and then placed in Petri dishes. Ten fourth instar
larvae were introduced into each Petri dish. The development of the
larvae feeding on sprayed leaves discs was observed at 24, 48, 72 and
96 hours. Three parameters were recorded: mortality, larval stage and
adult emergence.
Aqueous extracts preparation: Aqueous extracts of Cymbopogon
schoenanthus leaves were obtained according to the following
methodology: 1) three years old leaves were harvested, chopped to fine
particles size and shade dried at room temperature for four days; 2)
three formulations, TS50, TS100, TS150, were obtained with 50 g, 100
g and 150 g respectively of chopped dried leaves infused in one liter of
water for 24 hours.
Effects of C. schoenanthus leaves aqueous extracts on the field:
In our investigation, different concentrations of aqueous extracts of C.
schoenanthus leaves were used as an integrated management approach
to the control of P. xylostella under field conditions. An untreated small
plot of cabbage was placed about 15 m from the test plots to serve as a
control. After one month in seedbed, the seedlings were transplanted
to the plots. Plot size was 3.50 m × 1.20 m each, with a spacing of 75
cm between plants and 60 cm between rows, to create two rows of 5
plants each. Spacing between plots and replications were 1.5 m and
1.5 m, respectively. Before the planting, 30 kg of organic manure
collected from extensive poultry farming was applied to each plot. The
seedlings were sprinkled with water two times per day. No insecticide
was used in the seedbed, but after the planting, the organophosphorus
insecticide dimethoate was used weekly at 400 g of active ingredient
per hectare (the dose indicated by manufacturer) to control DBM on
every plot until the pre-heading stage. After this phase, three doses of C.schoenanthus aqueous extracts (TS50: 50 g/l, TS100: 100 g/L and
TS150: 150 g/L) were applied weekly at a rate of 6 liters for the 4 plots
during 4 weeks. One liter of dimethoate prepared solution was used
for 4 plots, and the treatment was stopped 15 days before harvest to
respect persistence time. Sprays were applied with a manually operated
knapsack sprayer at 1.5 liter per treatment. A randomized complete block design (RCBD) with four treatments replicated four times was
used. At harvest, variables recorded for analysis were the yield, the
circumference, the weight of the heads. For damage analysis, the
cabbage leaves were classified according to the level of the perforations
caused by the larvae (Table 1).
Table 1:Classification of cabbage leaves damaged.
Statistical analysis
Significant differences among data concerning cabbage head
circumference, weight, yield, level of damage, and P. xylostella larval
mortality and adult eclosion were determined with analysis of variance
using Systat 5.0 software. Pairwise comparisons were done using the
Fisher LSD at p < 0.05. All data are presented as means ± standard
deviation.
Results
Toxicity of C. schoenanthus oil to P. xylostella larvae (contact
test)
The formulations THE1 and THE2 of C. schoenanthus emulsified
oil caused a faster mortality of the larvae than dimethoate suspension.
The mean survival times in a group of 10 larvae were 22, 33 and 44100
seconds respectively for THE1, THE2 and dimethoate (Table 2).
Larvae mortality time was significantly lower in the C. schoenanthus emulsified oil treatment compared to the control dimethoate (ANOVA:
F0.05(4)=333.73; P<0.001). Thus C. schoenanthus emulsified oil acts more
quickly than synthetic insecticide used in the present study. Larvae
treated with the soap preparation (SW) survived for 330 seconds.
Table 2: Mean survival time of the larvae of P. xylostella after treatment with emulsified
oil of C. schoenanthus (100% mortality).
Nutrition Test
The results in Table 3 showed that different concentration of
pesticide tested affected differently the instars of P. xylostella larvae.
Feeding damage was observed on the leaf discs after 24 hours
indicating that the larvae fed on the leaves. Generally, THE2, SW and
DT treatments caused similar death rates, which ranged from 5-12.5%.
This value turned around 10%. These formulations did not differ
significantly from each other. However, larval mortalities were 25%
and 60%, respectively, at 24 h and over 48 h for THE1. A significant
effectiveness against larvae of P. xylostella was observed when cabbage
leaves were treated with THE1 dose (ANOVA: F0.05(4)=26.25; P<0.001). As in the contact or feeding tests, the formulation THE1 appeared more
effective. Figure 1 reports percentage of P. xylostella adult eclosion
at 96 hours. Concerning the absolute control by the DW and THE2
treatments, 95% and 65% adults, respectively, have evolved. THE1
(7.5%) significantly (ANOVA: F0.05(4)=9.5; P<0.005) prevented the adult
evolution than DW, SW and THE2. The adult eclosion rate recorded
with dimethoate was 37.5%.
Table 3: Mean percentage of larvae mortalities induced by the insecticides and
larvae developing to pupal stage.
Figure 1: Evolution of the larvae of P. xylostella towards the adult forms at 96
hours.
Harvest Data
Overall, insect populations were low. Generally, it was observed
that the cabbage plants thrived well, and all the harvested heads of
cabbage from each treatment plot were marketable. First attacks began
at pre-heading stage, and an ave rage of 3-5 larvae were recorded per
10 plants. By comparing the various treatments at the harvest period,
a strong presence of larvae (more than 4 larvae per 10 plants) was
observed on certain heads harvested from the dimethoate-treated
plot. However, the heads treated with dimethoate were slightly larger
than those treated with the botanical aqueous extracts: 61.70 ± 3.71
cm versus 59.85 ± 5.86 cm; 59.53 ± 1.96 cm and 60.32 ± 2.86 cm for
TS50, TS100 and TS150 respectively. The head weight also showed a slight difference between the dimethoate treatment and the botanical
extracts: 1.69 ± 0.32 kg versus 1.41 ± 0.36; 1.57 ± 0.31 kg and 1.56 ±
0.19 kg for TS50, TS100 and TS150, respectively (Table 4). There were
no statistically significant differences between the dimethoate and
C. schoenanthus aqueous extract treatments (ANOVA: F0.05(3)=0.38;
P>0.7). The yield was slightly higher and the level of damage concerning
the heads harvested from control plot (dimethoate treatment) was
relatively of low quality compared to the treatments the aqueous
extracts the botanical aqueous extracts (4.22 ± 0.34 kg/m² and 2.30 ±
0.14 versus 3.45 ± 0.40 to 3.93 ± 0.28 kg/m² and 1.80 ± 0.72 to 2.22 ±
0.73 respectively). The ANOVA test for yield and damage parameters
showed also no significant difference between the insecticide and the
botanical treatment (ANOVA: F0.05(3=0.84; P>0.4).
Table 4: Effects of aqueous extracts of C. schoenanthus and dimethoate on cabbage
Yield and quality.
Discussion
The objective of this study was to investigate the activities of
aqueous leaves extracts and low concentrations of essential oil of C.
schoenanthus to control populations of P. xylostella and their larvae.
The aqueous leaf extracts of this plant were quite effective against P.
xylostella, and achieved the similar protection of cabbage to dimethoate.
The results of our investigation confirm the reports of Idrissou [36]
which revealed that both Azadirachta indica and C. schoenanthus extracts had equivalent efficiency against DBM of cruciferous plants.
The observations showed that the essential oils of C. schoenanthus can cause effective mortality of P. xylostella larvae. The essential
oil extracted from C. schoenanthus contained a high percentage of
monoterpenes. Studies carried out in Togo showed that the major
component of C. schoenanthus extract was piperitone with a value
bordering 70% [37,33], and was responsible for the insecticidal activity
[35]. This component, isolated and purified by Author’s name [38],
had strong insecticidal activity against eggs, neonate larvae and adults
of Callosobruchus maculatus at very low concentrations [31]. These
observations corroborates the low concentrations of the formulation
THE1 (2 g/l) effective effect on larvae of P. xylostella in our study. This
formulation would ensure a good protection of cabbage against DBM.
It can validly used as alternative in P. xylostella management.
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