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.
