Pandan Leaves (Pandanus amaryllifolius Roxb.) As A Natural Cockroach Repellent Li J.1 and Ho S.H.2 School of Biological Sciences, National University of Singapore 10 Kent Ridge Crescent Singapore 119260 ABSTRACT Seven compounds and fractions prepared from pandan leaves (P. amaryllifolius) were evaluated for repellent activity against Blattella germanica (L.) using a modification of the linear tract olfactometer. 2-Acetyl-1-pyrroline, pandan essence and the hexane-pandan extract were repellent (65-93 % repellency) at all concentrations tested; the acetone-pandan extract was attractive at increasing concentrations (minimum of 62 % attractancy); artificial pandan flavouring and the dichloromethane-pandan extract gave erratic results. Undiluted crude aqueous pandan extract displayed an attractancy of 62%. The potential of P. amaryllifolius as a natural and environmentally friendly pest management tool is discussed. INTRODUCTION It is said that taxi drivers in Singapore and Malaysia keep bunches of pandan leaves (Pandanus amaryllifolius Roxb.) in their taxis to ward off cockroaches. An analysis of the volatile essential oils of P. amaryllifolius by MacLeod and Pieris (1982) revealed that this species contains mainly terpenes and sesquiterpene hydrocarbons (6-42%), as well as a major aroma component – 2-acetyl-1-pyrroline (2AP) (Yoshihashi, 2002). The presence of essential oils, i.e. mixtures consisting predominantly of mono- and sesquiterpene derivatives, accounts for the insect-repellent and attractant properties associated with some aromatic plants (Herout, 1970; Rice, 1983). Previous studies have established significant repellent activity of P. amaryllifolius against American cockroaches (Periplaneta americana L.) (Ahmad et al, 1995), but similar effects against other species of cockroaches have not yet been looked into. This study thus evaluates seven components – four essential oils extracted with alcohol, n-hexane (CH3(CH2)4CH3), acetone (CH3COCH) and dichloromethane (CH2Cl2) respectively, an artificial pandan flavouring (Star Brand), an aqueous crude extract and an aromatic compound, 2-acetyl1-pyrroline (2AP) (C6H9NO) - from P. amaryllifolius as repellents against German cockroaches, Blattella germanica (L.). MATERIALS AND METHODS Test Insects Nymphs of B. germanica (Universiti Sains Malaysia strain),1-6 days old, were used for the experiments. Test Chemicals Artificial pandan flavouring (Star Brand) was purchased from a local supermarket, natural pandan essence extracted using 50% alcohol was provided with compliments from PT Haldin 1 2
Student Associate professor
Pacific Semesta while 2AP (C6H9NO) in 1% dichloromethane solution was obtained from JIRCAS1 (courtesy of Dr T. Yoshihashi). Fresh pandan leaves were provided by Dr Saw Seang Mei, Department of Community, Occupational & Family Medicine, NUS. The plant was also acquired from Malaysia as well as local wet markets. Boiled pandan leaf crude extract was obtained by boiling 19.8 g (wet weight) of mature leaves for 30 min in 800 mL of distilled water and then filtered. The filtrate was used. The rest of the leaves were subjected to cold solvent extraction. Approximately 10 kg of leaf mass were were bathed for one week in analytical grade n-hexane (CH3(CH2)4CH3), acetone (CH3COCH) and dichloromethane (CH2Cl2) respectively. Bioassay Procedure A linear track olfactometer used for detecting the repellency response of nymphs to the aroma in pandan extracts was adapted from Sakuma and Fukami (1985). Repellency Assay In the repellency test, the effectiveness of each candidate extract was expressed in terms of the excess proportion of insects on the treatment area (Bentley, 1944): NS − NC I = NS + NC NS PC = 1 − × 100% NS + NC PS = 100% − PC where I : excess proportion index NS : number of insects trapped in the chemical-treated test chamber NC : number of insects trapped in the control test chamber PC : Percentage repellency (i.e. percentage of animals...
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