Cobra-repellent activity of Eryngium foetidum L. (Andu) and Aquilaria ugallocha (Agil)

Abstract

Foliage of Andu, Eryngium foetidum L., is traditionally used in Sri Lanka to repel cobras, Naja naja naja L. Application of aqueous suspension of crushed Andu leaves, spreading dried leaves and growing Andu plant in agricultural lands and residential areas are the traditional practices used to repel cobras. Burning of Agil wood is also used traditionally in Sri Lanka to repel cobras. These traditional practices indicate the presence of compounds in Andu and Agil that may have a repellent activity against cobra. Therefore, identification of volatile repellents present in Andu and Agil plants might possibly lead to a semiochemical based management program to control cobra population. Active compounds present in Andu and Agil were collected by steam distillation. Repellent activity of extracts obtained from steam distillation was assayed against cobra using a two-choice laboratory bioassay. A dilution series of the extracts (20, 10, 1, 0.1 and 0.01 mg/ 25 pL pentane) was prepared using pentane. For each bioassay, two baits (one day old chicks) were treated, one with 25 pL of the test extract and the other with 25 pL of pentane. It was visually observed that whether the cobra uses bait stations as prey within 15 minute time period. Each treatment was replicated five times. Bioassay showed that steam-distilled extracts from both plants associate with very strong repellent activity on cobra. Dose-response bioassay showed that the maximal activity associates with 0.1 mg equivalent of steam distillate of Andu and 1 mg equivalent of steam distillate of Agil. Thin layer chromatographic and gas-liquid chromatographic analysis of steam distillates showed that the extracts contain more than one compound. Therefore, the repellent' activity of Andu and Agil may be associated with one or more compounds present in steam distillate.