Chemical composition and larvicidal activity against Aedes aegypti larvae of essential oils from four Guarea species.

The essential oils of four Guarea species collected at Manaus (Amazonas, Brazil) were obtained by hydrodistillation and analyzed by GC-MS. Except for one diterpene detected, the compounds identified in the essential oils were hydrocarbons and oxygenated sesquiterpenes. The major sesquiterpenes were alpha-santalene (26.26%) and alpha-copaene (14.61%) from G. convergens branches; caryophyllene epoxide (40.91%) and humulene epoxide II (14.43%) from G. humaitensis branches; cis-caryophyllene (33.37%) and alpha-trans-bergamotene (11.88%) from G. scabra leaves; caryophyllene epoxide (36.54%) in leaves and spathulenol (14.34%) in branches from G. silvatica. The diterpene kaurene (15.61%) was found in G. silvatica leaves. Larvicidal activity assay of essential oils against third-instar Aedes aegypti larvae revealed that at higher concentrations (500 and 250 microg/mL), all the essential oils caused 100% mortality after 24 h of exposure. The most active essential oils were those of G. humaitensis branches (LC(50) 48.6 microg/mL), G. scabra leaves (LC(50) 98.6 microg/mL) and G. silvatica (LC(50) 117.9 microg/mL). The differences in the toxicity of essential oils of Guarea species on A. aegypti are due to qualitative and quantitative variations of the components, therefore the larvicidal effect may be due to higher amount of the sesquiterpenes with caryophyllane skeleton.