Eucalyptus species, mosquito repellents

Eucalyptus citriodora Hook f (Lemon gum) The oil of the fresh leaves of E. citriodora (2.2-8.3%), a tree introduced into Kenya from Australia (68), has been well researched in Kenya. Results indicate that there are two chemical varieties that were introduced. The chief essential oil constituents of one variety are citronellal (65-88%), citronellol (2-25%) and isopulegol (2-19%). In constrast, the second variety has as its major essential oil consitutents citronellol (32-52%), citronellal (38-59%) and 1,8-cineole (2-19%) (68,69). The essential oil is regarded as a perfumery oil. This plant is the second most commercially important Eucalyptus species in the essential oil trade and is only second to E. smithii Baker (69). The aromatic oil is used in soaps, creams and lotions due to its desirable odor properties, and as with many other essential oils is also used extensively in many technical preparations to mask other industrial malodors. A highly active mosquito repellent compound, p-menthane 3,8-diol has been isolated from the waste water of distillation of E. citriodora. There are now many commercial mosquito repellents based on this waste water (70-73). 

Some Australian native plants had been associated with the treatment and/or prevention of mosquito-borne disease. There have been suggestions that the bark of tropical rainforest tree Alstonia scholaris (L.) R. Br. (dita bark) has been used as an antimalarial, but clinical trials have shown that alkaloids in the bark of this, and the closely related species Alstonia constricta F. Muell. (bit-terbark), have little antimalarial activity. Eucalyptus globulus Labill (Tasmanian blue gum) had sometimes been referred to as fever prevention tree with a belief that the use of the oil prevented malaria. Similarly, many anecdotal reports of Melaleuca quinquenervia (Cav.) S. T. Blake (broadleaved paperbark) may prevent disease by repelling mosquitoes. Unfortunately, there is no current evidence that Australian native plants provide a suitable treatment for malaria. ... 

The botanical insect repellents, cinnamon oil, lemon eucalyptus oil, sandalwood oil, and turmeric oil, were evaluated in the laboratory against fourth instars of Aedes aegypti, Aedes albop-ictus, and Culex pipiens complex. The sandalwood oil was the most effective larvicide, killing the larvae of all three species of mosquitoes in a relatively short time. Twenty-one commercial insect repellents shown in Table 21.3 including 12 natural, 6 deet-based, and 3 synthetic repellent products were evaluated as larvicides against the larvae of Aedes albopictus in the laboratory. Ten of the 12 botanical products at 0.1% concentration provided 57%-100% mortality at 24 hours posttreatment. " ... 

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