Components from Sri Lankan <i>Piper betle</i> L. leaf oil and their analogues showing toxicity against the housefly, <i>Musca domestica</i>

The essential oil extracted from <i>Piper betle</i> L. leaf using pilot plant steam distillation was tested against the adult housefly, <i>Musca domestica</i>, for insecticidal activity. LC₅₀ values at the end of 24 and 48 h exposure periods were 10.3 and 8.7 mg/dm³, respectively. Ceylon citronella oil (<i>Cymbopogon nardus</i>) used as a standard showed LC₅₀s of 26.5 and 24.2 mg/dm³ for the same exposure periods. Bioassay-guided fractionation of <i>P. betle</i> leaf oil revealed safrole and eugenol as the active principles against <i>M. domestica</i>, safrole showing LC₅₀ values of 4.8 and 4.7 mg/dm3, and eugenol 7.3 and 6.2 mg/dm³ for the 24 and 48 h exposure periods, respectively, while citronellal (synthetic standard) showed equal LC₅₀ values of 14.3 mg/dm³ for the same exposure periods. Using safrole as the starting compound, eight analogues were prepared to study structure–activity relationships. Among the eight analogues, dihydrosafrole gave almost equal mortality at LC₅₀ 4.7 mg/dm³ as that of the parent compound safrole after 24 and 48 h exposure, but isosafrole was twice as active as safrole, showing LC₅₀ values of 2.3 and 2.2 mg/dm³ for the 24 and 48 h exposure periods. Our GC–MS studies on Sri Lankan <i>P. betle</i> leaf oil show that it contains safrole (52.7%), allylpyrocatechol diacetate (15.4%), eugenol (6.4%) and eugenyl acetate (5.8%) as the major components. Here we also present the GC–MS profile of fractions of Sri Lankan P. betle leaf oil.