Ethnobotanical Leaflets 12: 1096-1101.
2008. Biopesticidal Effect of Leaf Extracts
of Catharanthus roseus L
(G) Don. on the Larvae of Gram Pod Borer - Helicoverpa
armigera (Hübner) 1School
of Biotechnology, Chemical and Biomedical 2 P G
and Research Department of Botany, 3Department
of Botany, RD Issued
Biopesticides have gained prominence as potential plant
protecting agents. Biological activity of solvent extracts of Catharanthus roseus L (G) Don. were evaluated against larvae
of gram pod borer Helicoverpa armigera (Lepidoptera: Noctuidae).
Antifeedant and larvicidal
activity of methanol crude, petroleum ether, methanol fraction and ethyl
acetate fraction of leaf extracts of C.
roseus were estimated in the present study. Preliminary
screening of the extracts was tested at a concentration of 1,000 ppm. The larval mortality was observed after 24h of
exposure to the extracts. All extracts exhibited moderate larvicidal
effects. However, highest larval mortality was observed in ethyl acetate
fraction (4.1, 4.1, 17.4, 42.2, 55.6 and 84.5) of leaf extract of C. roseus,
followed by methanol fraction (10.6, 12.7, 26.9, 59.4, 68.3 and 106.7)
against the I, II, KEYWORDS: Helicoverpa armigera; Catharanthus roseus;
Biopesticide;
Antifeedant. INTRODUCTION Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is a polyphagous pest that infests cotton, tomato, bhendi, chickpea, pigeonpea, chilli, maize, sorghum and many other crops, inflicting substantial crop losses every year (Reed and Pawar, 1982; Manjunath et al., 1989; Sharma, 2001; Talekar et al., 2006). However, colonization of new host by H. armigera induces selection of adaptive characters and genetic differentiation in population (Rice, 1987; Diehl and Bush, 1989). Larvae of H. armigera feed on the leaves initially and later bore into the pods and seeds with its head thrust into, while rest of the body lies outside. Hence, a large number of H. armigera larvae in cotton and other vegetables survive to adults that may disperse widely, producing progeny that damage high-value crops (Cabanillas and Raulston, 1995; Michael and Donald, 1996). Since, H. armigera can survive on alternate host it is characterized by high mobility and fecundity. Further, it has been reported to develop resistance to synthetic insecticides used in its management (Ramasubramaniam and Regupathy, 2004). During the last 50 years, worldwide use of synthetic insecticides to control insect pests has led to both insecticide resistance and environmental persistence (Roush and Tabashnik, 1990). Alternatively, phytochemicals have been used in the management of agricultural pest (Choudhary et al., 2001). Plant derived pesticides are eco-friendly, non-toxic to non target organisms, non persistent in nature, besides they are lees known to promote drug resistance (Liu et al., 2000). Application of bio-pesticides has been reported to have positive impacts on bollworm population management (Ge and Ding 1996; Ramya et al., 2008). Therefore, researchers world over are engaged in a mission to hunt for novel phytochemicals that could potentially be used in the management of insect-pests. Plants are endowed with a potential to produce a wide range of allelochemicals that protect the plants from insect-pests. However, production of phytochemicals has been reported to vary from plant to plant (Ahmad, 2007). Further, parameters like age of the plant, part of the plant (root, stem, leaf, fruit, flower, seed and bark) have been reported to affect the production of such allelochemicals. The phytochemicals produced in response to insect-pest attack, affect feeding and oviposition of insects on the plants (Ramya et al., 2008). A number of plants have been shown
to have pesticidal and antifeedant
activity against H. armigera,
of which Neem has been subjected to extensive
investigation (Koul, 1985; Chopra et al., 1994; Jaglan
et al., 1997; Koul et al., 2000). Studies have
shown that Acorus calamus, Annona squamosa, Vitex negundo are effective
in the management of H. armigera (Murugan et al., 1998; Janardhan
et al., 1999). Sundararajan and Kumuthakalavalli,
(2001) evaluated antifeedant activity of aqueous
extract of Gnidia glauca
and Toddalia asiatica
against H. armigera.
With this background, in the present study the pesticidal
effect of leaf extracts of C. roseus has been evaluated against the larvae of H. armigera. C. roseus (Madagascar periwinkle) belongs to the family Apocynaceae. Pharmacological studies have revealed that C. roseus contains more than 70 different types of alkaloids (indole alklaloids) and chemotherapeutic agents (Verpoorte, 1998). Also, in vitro studies have shown that this plant produces large number of alkaloids upon elicitation (Verpoorte et al., 2002). The enormity of work conducted on this medicinal plant is so large that since 1950s more than 2500 publications have come in, ironically, only handful of data is available with regard to its bio-pesticidal potential. MATERIALS Collection of Plants C.
roseus was collected from the wild in Extraction of phytochemicals
using different solvents Leaves were collected, washed
thoroughly in water, air dried in shade and powdered using a pulverizer and stored in plastic containers. The powdered material was weighed
and extracted in crude methanol (40-60 %) as solvent in the ratio of Test organism: The larvae used for the study were collected from the host plants in the fields and brought to lab. They were reared on artificial diet under laboratory conditions. Studies were carried out using I-VI instar larvae of H. armigera against the leaf extract of C. roseus. The percentage mortality was calculated after a period of 24 h. Bioassay studies Bioassay studies were carried out with different fractions of C. roseus leaf extracts against the larvae of H. armigera. The studies were conducted (24 h) in the laboratory in transparent plastic containers of 4x2.5 cm size capped with perforated plastic lids. Fresh leaves of Gossipium esculentum (Cotton) were collected from the field and washed in clean water. Excess moisture was removed and the leaves were dipped in one percent test solution, shade dried and served to the larvae of H. armigera. Extract free leaves served as the control. For each treatment 10 larvae were singly introduced in separate containers after six hour starvation. Three replicates each of ten larvae were maintained for each treatment. The experiments were conducted at 27±1℃, 75% humidity and 14h dark period. Twenty four hour larval mortality was observed and the percentage mortalities were corrected using Abbott’s formula (Abbott, 1925). Ethyl acetate fraction of C. roseus was tested for LD50 values against the larval stages of H. armigera. Mortality was observed after the completion of the larval stages. The fraction which showed high rate of mortality in the least LD50 values was selected for further studies. RESULTS The results of bioassay studies against the larvae of H. armigera in the crude extracts, methanol fractions, petroleum ether fractions and ethyl acetate factions of C. roseus revealed that the LD50 values for the individual fractions of plant extracts varied significantly. The least LD50 values ranged from 4.14 to 84.54µg/cm2 for I to VI instars larvae in the ethyl acetate extracts of leaves of C. roseus (Table 1). The mortality rate was observed in the decreasing order of ethyl acetate fraction > methanol fraction > methanol crude > petroleum ether. The ethyl acetate extracts of C. roseus was found to be more active than other fractions tested. Therefore, ethyl acetate extracts of C. roseus were used to determine the ED50 values for their effect on the larvae of H. armigera. The ED50 values and its corresponding fiducial limits along with slope and intercept are given in Table 2. However, it was observed that the LD50 values were significantly different at P<0.05, LSD: 6.334. DISCUSSION Plants produce a wide spectrum of allelochemicals, however, many
of such chemicals have not been explored for their physiological significance
(Norduland and Sauls,
1981). These phytochemicals specifically inhibit
growth, morphogenesis, metamorphosis and reproduction (Ahmad, 2007).
Currently there is resurgence of interest in plant derived compounds for developing
them commercially as ecofriendly insecticides.
Tropical plants are more promising for the development of new insecticides
(Jacobson and Crosby, 1971). Despite, the fact that hundreds of tropical
plants are reported to possess insecticidal property, only few compounds (Azadirachtin) have been commercialized (Chopra et al., 1994). For successful
exploitation of natural insecticidal compounds, screening for their
behavioral and physiological effects in poly-phagous
insects with an understanding of structure activity relationship is
essential. Unfortunately, many do not provided
estimates of critical lethal (LD50) or critical effective dose (ED50)
which prevents feeding or emergence as adults. Nevertheless, such values evaluate
the relative efficacy of the extracts and are required for field application.
In a study, Simmonds et al (1990) reported high antifeedancy
(low ED50) for pure compounds isolated from different plants against
the larvae of H. armigera.
Janarthan et
al (1999) showed that 0.2 and 0.5 % petroleum ether extracts of Parthenium histerophorus
exhibited 100% feeding difference in H.
armigera. Similarly, aqueous extracts of Calotropis procera and
Datura stromonium have
been shown to display about 90% feeding protection against H. armigera (Dodia et al., 1998).
The
bioactivity of tested phytochemical extracts varied
significantly with solvents used for the extraction and instar
stage of the larvae. Reviewing the prospects of antifeedant
for the management of pests, Jermy (1990) and Ahmad (2007) reported that plant extracts/compounds “with
combined behavioral and toxic effect are more likely to have successful
practical application than the compounds/extracts, which evoke only
behavioral effect of antifeedancy”. Briefly,
considering the information available in literature on antifeedancy
of plant extracts, the present study has shown that there is a wide scope for
application of ethylaceteate fraction of C. roseus as
larvicidal/ antifeedant agent
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Table 2. Larvicidal effect of ethyl acetate fractions of C. roseus on
the larvae of H.
armigera.
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