Larvicidal activity of Kaempferia galanga rhizome phenylpropanoids towards three mosquito species

BACKGROUND: This study was aimed at assessing the toxicity of ethyl cinnamate and ethyl p-methoxycinnamate (EMC) identified in Kaempferia galangal L. (Zingiberaceae) rhizome and another 12 known compounds to third-instar larvae from laboratory-reared Culex pipiens pallens Forskal, Aedes aegypti L. and Ochlerotatus togoi Theobald and field-collected C. pipiens pallens (Jinhae colony). Results were compared with those for fenthion and temephos. RESULTS: Ethyl p-methoxycinnamate was the most toxic of the test compounds to larvae of the three mosquito species (LC(50) 12.3-20.7 mg L(-1)) but less toxic than either fenthion (0.0096-0.021 mg L(-1)) or temephos (0.0039-0.0079 mg L(-1)). Ethyl cinnamate and 3-carene were highly active against C. pipiens pallens larvae (24.1 and 21.6 mg L(-1)) but less toxic to A. aegypti and O. togoi larvae (ca 40 and 60 mg L(-1) respectively). The toxicity of these compounds to larvae from the Jinhae colony of C. pipiens pallens was almost the same as their toxicity to the laboratory-reared larvae, although the larvae from the colony exhibited low levels of resistance to fenthion (resistance ratio 9.1) and temephos (5.8).CONCLUSION: Kaempferia galanga rhizome-derived materials, particularly ethyl p-methoxycinnamate, merit further study as potential mosquito control agents for protection of humans and domestic animals from vector-borne diseases and nuisance caused by mosquitoes.