Control of stored grain pest, Callosobruchus ...

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Control of stored grain pest, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) using the essential oil isolated from Plectranthus zeylanicus a

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B.A.H.E. Balachandra , P.U. Pathirathna & P.A. Paranagama

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Department of Chemistry, University of Kelaniya, Kelaniya, Sri Lanka Version of record first published: 21 Dec 2011

To cite this article: B.A.H.E. Balachandra, P.U. Pathirathna & P.A. Paranagama (2011): Control of stored grain pest, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) using the essential oil isolated from Plectranthus zeylanicus , Natural Product Research: Formerly Natural Product Letters, DOI:10.1080/14786419.2011.643883 To link to this article: http://dx.doi.org/10.1080/14786419.2011.643883

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Natural Product Research 2011, 1–4, iFirst

SHORT COMMUNICATION Control of stored grain pest, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) using the essential oil isolated from Plectranthus zeylanicus Downloaded by [Wayne State University], [Pavithra Pathirathna] at 11:15 29 June 2012

B.A.H.E. Balachandra, P.U. Pathirathna and P.A. Paranagama* Department of Chemistry, University of Kelaniya, Kelaniya, Sri Lanka (Received 20 March 2011; final version received 9 September 2011) The bruchid, Callosobruchus maculatus (F.) causes major losses during the storage of cowpea seeds [Vigna unguiculata (L.)Walp.] in Sri Lanka. Essential oil isolated from Plectranthus zeylanicus plant was tested for potential insecticidal activity against C. maculatus. The gas chromatography studies of the essential oil of P. zeylanicus showed that -cymene (3.5%), -caryophyllene (0.2%), geranyl acetate (9.3%) and geraniol (7.2%) were the major constituents. The adults of C. maculatus were susceptible to both fumigant and contact toxicity of P. zeylanicus plant oil. LC50 values of 0.927 and 0.010 g L1 were obtained for fumigant toxicity and contact toxicity assays, respectively. Oviposition and F1 adult emergence were significantly inhibited by P. zeylanicus plant oil at a concentration higher than 0.001 g L1 in both fumigant and contact toxicities. The analysis of olfactometer and choice camber bioassays revealed the repellent effects of the oil of P. zeylanicus plant. Keywords: Plectranthus zeylanicus; Callosobruchus maculatus (F.); essential oil; cowpea

1. Introduction Cowpea [Vigna unguiculata (L.)Walp.] is one of the most important food legume crops in the semi-arid tropics covering Asia, Africa, southern Europe and Central and South America. It is an alternative source of dietary proteins and other essential nutrients. The insect infestation of the seeds during storage of cowpea causes weight and quality losses that lead to a reduction of commercial values and seed germination. The major pest encountered in cowpea grain stacks and storage premises is the cowpea bruchid, Callosobruchus maculatus (F). These insects are currently controlled in warehouses by fumigating with synthetic chemicals such as pirimiphos methyl and phosphine (Singh, 1990). Phosphine (PH3) is the most widely used fumigant for disinfesting stored grain in warehouses. The use of synthetic pesticides has significant drawbacks including insecticide residues on grains, threat to human health and the environment, increased costs and handling hazards. The use of plant materials by mixing several parts such as leaf, bark, seed and vegetable oil is an ancient measure in many parts of the world. Recently, as an alternative pest control technology, essential oils and their constituents have attracted attention because of their low toxicity to warm-blooded mammals and their high volatility.

*Corresponding author. Email: [email protected] ISSN 1478–6419 print/ISSN 1478–6427 online ß 2011 Taylor & Francis http://dx.doi.org/10.1080/14786419.2011.643883 http://www.tandfonline.com


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Essential oils are the volatile materials derived by a physical process from an odorous plant of a single botanical form and categorised under plant secondary metabolites. In the past few years, the repellent activity of several essential oils has been investigated against many insects (Adhikari, Paranagama, Abeywickrama, & Bandara, 2002; Jayasingha, Warnasooriya, & Dissnyk, 1999). The toxicity and repellent effects of various essential oils have been reported against many insects (Ketoh, Glitho, Koumaglo, & Garneau, 2000; Paranagama, Adhikari, Abeywickrama, & Bandara, 2002). Plectranthus zeylanicus, called Iriweriya, has a delightful, strong and unique sweet lemon scent and is a perennial herb and about 60–90 cm tall, with a branched stem found in the mid and low country elevations in Sri Lanka. The herb has aromatic, astringent and stomachic properties and is used in decoction for fevers, dysentery, diarrhoea, vomiting and thirst. The authors’ continuing efforts in the development of stored grain pest control agents from essential oils resulted in the identification of Cymbopogon citratus, Alpinia calcarata Rosc., Cinnamomum zeylanicum leaf oil, Cinnamomum zeylanicum fruit oil and Micromelum minutum leaf oils as potential stored grain protectants (Abeywickrama, Adikari, Parangama, & Gamge, 2006; Paranagama & Gunasekara, 2011; Paranagama et al., 2002). This investigation examined the toxicity and the repellent activity of essential oils of P. zeylanicus plant against the cowpea pest C. maculatus. 2. Results and discussion 2.1. Analysis of essential oil of P. zeylanicus The laboratory steam-distilled essential oil of P. zeylanicus (UOK-SL/05-09) gave a dark orange oil with a spicy odour. The yield of the essential oil of P. zeylanicus was 0.2% (w/w). The gas chromatography studies of the essential oil of P. zeylanicus showed that -cymene (3.5%), -caryophyllene (0.2%), geranyl acetate (9.3%) and geraniol (7.2%) were the major constituents. 2.2. Contact and fumigant toxicities of P. zeylanicus plant The oil of P. zeylanicus showed both contact and fumigant toxicities to C. maculatus. The adult mortality sharply increased when exposed to higher concentrations (Table 1). The percentage mortality of test insects was significantly different from control- and

Table 1. Percentage mortality, mean number of eggs laid by adult C. maculatus and mean number of F1 adult emerged during contact toxicity bioassay. Treatment (g L1) Control (non-treated) Ethanol 0.001 0.005 0.05 0.5 1.0 2.0

Percentage mortality

Mean number of eggs þ SE

Mean number of F1 adult þ SE

1.67 1.66a 1.67 1.66a 31.67 3.07b 51.67 3.07c 81.67 3.07d 100.00 0e 100.00 0e 100.00 0e

139.00 2.85a 143.83 2.72a 95.00 2.67b 70.50 4.65c 40.33 2.55d – – –

120.33 2.62a 125.67 1.94a 79.83 3.71b 53.00 4.41c 27.67 1.58d – – –

Notes: The results were analysed using one-way ANOVA and Tukey’s pair-wise comparison test (p 5 0.05). Means with the same letters do not differ significantly.


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ethanol-treated samples in fumigant toxicity and contact toxicity assays at the doses higher than 0.005 and 0.001 g L1, respectively. Probit analysis found the LC50 to be 0.927 and 0.01 g L1 in fumigant and contact bioassays, respectively. Plectranthus zeylanicus plant oil significantly (p 5 0.05) reduced the number of eggs laid and the number of F1 adults emerged of C. maculatus in both contact and fumigant bioassays (Tables 1 and 2) with increasing concentration. The suppression of F1 adult emergence of C. maculatus in essential oil-treated sample was likely due to the eggs being killed by the essential oils, since no development of abnormalities or bodies of dead larvae were observed. The reduction of oviposition in stored grain pests has been reported for other essential oils such as C. zeylanicum, M. minutum (Paranagama & Gunasekara, 2009), A. calcarata (Abeywickrama et al., 2006) and nutmeg (Huang, Tan, Kini, & Ho, 1997). 2.3. Repellent activities of the oil of P. zeylanicus plant 2.3.1. Olfactometer bioassay According to the results obtained during olfactometer bioassay, the percentage response of C. maculatus was significantly decreased with the increase of volatile dose in all oil samples. 2.3.2. Choice chamber bioassay The choice chamber bioassay was also carried out to evaluate the repellent effects of the oil of P. zeylanicus plant. Oil repelled the adult C. maculatus, as significantly more bruchids were found in the control bottles than oil treatments. At doses higher than 0.1 mg, the percentage of insects responding to P. zeylanicus oil was significantly lower ( p 5 0.05) from ethanol- and control-treated samples. The results obtained for the control and ethanol showed the highest percentage of insects. The results were not significantly different from each other indicating that the use of ethanol has no effect on insect repellence. The authors believe that the results of this study demonstrate the contact toxicity, fumigant toxicity and repellent activity of P. zeylanicus oil against cowpea bruchids C. maculatus. Even though the oil is used in many different industries, no efforts have previously been made to identify the potential of P. zeylanicus plant oil or its components to be developed as grain protectants to control cowpea infestation by

Table 2. Percentage mortality, mean number of eggs laid by adult C. maculatus and mean number of F1 adult emerged during fumigant toxicity bioassay. Treatment (g L1) Control (non-treated) Ethanol 0.001 0.005 0.05 0.5 1.0 2.0

Percentage mortality

Mean number of eggs þ SE

Mean number of F1 adult þ SE

1.67 1.67a 1.67 1.67a 6.67 3.33a 11.67 3.07ab 18.33 3.07b 41.67 3.07c 66.67 4.94d 83.33 4.21e

147.50 3.94a 152.17 1.17a 150.33 2.26a 102.17 2.87b 113.87 4.65b 82.00 3.40c 52.00 4.13d 34.33 6.14e

134 1.98a 138.17 2.09a 136.17 2.09a 99.67 5.33b 89.67 2.23b 65.50 2.40c 37.67 3.78d 26.33 2.69d

Notes: The results were analysed using one-way ANOVA and Tukey’s pair-wise comparison test (p 5 0.05). Means with the same letters do not differ significantly.

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bruchids. Further investigations are needed to identify the bioactive compounds of test oils and their effect on non-target organisms.


3. Conclusions The essential oil of P. zeylanicus could be used to develop a commercial product for the protection of stored cowpea from bruchid infestation. Field trials should, however, be conducted to assess the cost-effectiveness and feasibility of using P. zeylanicus plant oil before new products are formulated and commercialised. Acknowledgements The authors wish to thank the National Research Council and College of Chemical Sciences, Institute of Chemistry Ceylon, Sri Lanka, for the financial support.

References Abeywickrama, K., Adikari, A.A.C.K., Parangama, P., & Gamge, C.S.P. (2006). The efficacy of essential oil of Alpinia calcarata (Rosc.) and its major constituent, 1, 8-cineole, as protectants of cowpea against Callosobruchus maculatus (F.). Canadian Journal of Plant Science, 86, 821–827. Adhikari, A.A.C.K., Paranagama, P., Abeywickrama, K.P., & Bandara, K.A.N.P. (2002). Behavioral studies of cowpea bruchid, Calloaobruchus maculatus (F.) against volatile extracts from leaves of lemongrass (Cymbopogon citrates), neem (Azadirachta indica) and curry leaf (Murraya koenigii). Tropical Agricultural Research, 14, 138–147. Huang, Y., Tan, J.M.W., Kini, R.M., & Ho, S.H. (1997). Toxic and antifeedent action of nutmeng oil against Tribolium castaneum (Herbst) and Sitophilus zeamais (Motosch.). Journal of Stored Products Research, 33, 289–298. Jayasingha, P., Warnasooriya, D., & Dissnyk, H. (1999). Lemongrass (Cymbopogon citratus): A literature survey – Medicinal and aromatic plant series (Vol. 9). Colombo, Sri Lanka: Information Service Center, Industrial Technology Institute. Ketoh, G.K., Glitho, K.H., Koumaglo, K.H., & Garneau, F.X. (2000). Evaluation of essential oil from six aromatic plants in Togo for Callosobruchus maculatus F. pest control. Insect Science and its Applications, 20, 45–51. Paranagama, P.A., Adhikari, A.A.C.K., Abeywickrama, K.P., & Bandara, K.A.N.P. (2002). Toxicity and repellent activity of essentials oils of Cymbopogon citratus (DC) Stapf. Murraya koenigii Spereng. against Callosobruchus maculatus (F.) (Coleoptera; Bruchidae). Journal of Tropical Agricultural Research and Extension, 51, 22–28. Paranagama, P.A. & Gunasekera, J.A. (2011). The Efficacy of the Essential Oils of Sri Lankan Cinnamomum zeylanicum fruit and Micromelum minutum leaf against Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), Journal of Essential Oil Research, 23(1), 75–82. Singh, S.R. (1990). Insects pests of tropical food legumes (p. 451). Chichester, NY: John Wiley.