Toxicity and repellence of Taiwanese indigenous djulis, Chenopodium formosaneum, against Aedes albopictus (Diptera: Culicidae) and Forcipomyia taiwana (Diptera: Ceratopogonidae)

The biological activity of djulis (Chenopodium formosaneum) extracts was evaluated against mosquitoes and biting midges. Djulis extracts were relatively nontoxic to Aedes albopictus larvae. However, they showed interesting repellence against adult mosquitoes as estimated by the median effective dosages (ED₅₀). ED₅₀ values for djulis extracts against mosquito adults in descending order were: seed extracted with methanol (0.83 %), seed extracted with dichloromethane (0.66 %), leaf extracted with methanol (0.50 %), and leaf extracted with dichloromethane (0.40 %). Field tests also suggested that djulis methanol extracts were effective at about a 1 % level against biting midges (Forcipomyia taiwana). A total of 15 and 20 compounds accounting for 88.8 and 79.9 % in the seed and leaf extract, respectively were identified by gas chromatography coupled to mass spectrometry (GC–MS). Among these, 9, 12-octadecadienoyl chloride, (Z, Z) was found in both as well as being the major constituent in the leaf extract (35.7 %). Further studies on the repellent property of the extracts against mosquitoes and biting midges are warranted.