Leaf and Flower Extracts from the Dwarf Elder (Sambucus ebulus): Toxicity and Repellence against Cosmopolitan Mosquito-Borne Diseases Vectors

There has been no scientific evidence of the bioactivity of Sambucus ebulus (Adoxaceae) extracts against insects. Therefore, we extracted and chemically characterized the leaves and flowers of S. ebulus in methanol and water. The two crude extracts and some of the phenolic compounds and amino acids isolated were tested as larvicides against two cosmopolitan mosquito species, namely the Asian tiger mosquito (Aedes albopictus) and the common house mosquito (Culex pipiens). To better understand their mode of action, we evaluated the in vitro acetylcholinesterase inhibitor effect of crude extracts on the two mosquito larvae by means of a colorimetric method. In addition, the ovideterrent effect of the crude extracts against Ae. albopictus females ovipositing in the open field was evaluated. As there has been no scientific evidence of the bioactivity of Sambucus ebulus (Adoxaceae) extracts against insects, we chemically characterized S. ebulus leaves and flowers extracted in methanol and water. The crude extracts, phenolic compounds, and amino acids isolated were tested as larvicides against the fourth-instar larvae of Aedes albopictus and Culex pipiens (Diptera: Culicidae). To understand their mode of action, we evaluated the in vitro acetylcholinesterase (AChE) inhibitor effect of the crude extracts on the two mosquito larvae through a colorimetric method. Furthermore, the deterrent effect of the crude extracts against ovipositing Ae. albopictus females was assessed in the open field. Twelve phenylpropanoids and fourteen amino acids were detected in the extracts, with a prevalence of hydroxycinnamic acids and nonaromatic amino acids. The most toxic compound to Ae. albopictus larvae after 24 h was gallic acid, followed by the crude S. ebulus leaf extract; on Cx. pipiens, it was the crude flower extract. The AChE test showed higher inhibition on both mosquito species exerted by the leaf extract if compared to the flower extract, and it also deterred oviposition by Ae. albopictus females starting from the third day. The results indicated that vegetal extracts could effectively help in the integrated vector management of mosquitoes.