Characteristic blue haze of vapourised eucalyptus essential oil - Mt Sonder, MacDonnell Ranges, Albert (Elea) Namatjira (c1953)
Eucalyptus Leaf oil glands are visible as bright dots when illuminated via a smart phone.
The mosquito olfactory (smell) system plays a key role in prey seeking behaviour.
Mosquito Prey Tracking Behaviour shows olfaction plays a major role over long distances.
Essential Oil Diffuser
Aim and Expected Outcomes This aim of this research is to reduce the incidence of mosquito infestation within the internal and external campus environments during the peak mosquito breeding season.
The primary outcome of the research is to determine the effectiveness of commercial eucalyptus essential oil diffusers within staff and student areas of university buildings as well as to determine the Eucalyptus species that could reduce mosquito infestation more widely if planted on university grounds.
To achieve this we have formed an international interdisciplinary team (Team Eucalyptus) with expertise in botany, biochemistry and psychology to determine the effectiveness of different species of Eucalyptus essential oil vapour as a natural mosquito repellent. This environmentally sensitive and sustainable approach incorporates knowledge of the mosquito sensory, perceptual and behaviourial mechanisms together with the established mosquito repellent properties and unique biodiversity of the Eucalyptus species. Since the most effective mosquito repellent would be rendered entirely ineffective if it also repelled humans, the research will also incorporate measures of consumer acceptance and preference.
Background If Australia had a ‘National Scent’ it would undoubtedly be eucalyptus. Its pervasive presence is evident from the characteristic blue haze that shrouds Australian forests in summer. This phenomenon is due to heat vaporising the volatile oil produced by cells within the leaves of Eucalyptus. This aromatic bloom occurs naturally over the hot summer months and coincides with the peak mosquito breeding season. The distinctive aroma of eucalyptus reflects the powerful aromatic qualities of its chemical constituents, or terpenes, which differ dramatically across eucalyptus species. For example, the lemon-scented gum (Corymbia citriodora) essential oil contains particularly high concentrations of the terpene citronellal. Citronellal is one of the most powerful naturally occurring mosquito repellents according to the Centre for Disease Control and suggests Eucalyptus may provide a natural deterrent to mosquito infestation.
The effectiveness of aromatics like citronellal as a mosquito repellent is not surprising given that olfaction (sense of smell) is the primary means by which mosquitos detect prey. Mosquitos also use vision, heat and taste when sensing prey, however these generally only play a role when a mosquito has already found their target. To locate prey from a distance they rely on specialised sensory receptors in their antennae that are particularly sensitive to the C02 we exhale. An understanding of this and other more complex aspects of mosquito behaviour and sensory perception is essential to develop an effective repellent.
There are three important limitations to using Eucalyptus essential oil as a mosquito repellent that the present project seeks to address. The first is that, by their nature, volatile chemicals like citronellal disperse rapidly and so have not been widely used as personal insect repellent. The second is that the effectiveness of mosquito repellent applied to the skin maybe limited given the mosquito is less dependent on their sense of smell when in close proximity to prey. Thirdly, we know very little about the potential insect repellent properties of Eucalyptus.
Despite being native to Australia over 95% of Eucalyptus oil is now produced overseas. In fact, the entire global production is sourced from less than 20 species exported from Australia during the 19th century largely for their timber or wood-pulp yields (Coppen and Hone, 1992). In contrast more than 700 species of Eucalyptus have been identified in Australia. This unique biodiversity is evident in the wide variation in local aromatic Eucalyptus species, such as the Sydney peppermint (E. piperita), the Strawberry Gum (E. olida) and the rose-scented gum (E.macarthurii). Essential oil from Eucalyptus macarthurii has a particularly high potential as a mosquito repellent as it contains almost 58% of the terpene geranyl acetate which recent research has shown to be 100% effective as a mosquito repellent with ‘arm-in-cage’ type experiments (Logan et al. 2010).
Hypotheses The primary hypotheses we will test is whether eucalyptus oil vapour provides an effective natural repellent against mosquito infestation.
The secondary hypothesis is to test whether vapour derived from E.macarthurii proves a more efficient deterrent than comparison species (Corymbia citriodora, E. piperita and E.globulus).
The third hypothesis will test whether eucalyptus oil vapour provides a more efficient mosquito repellent than traditional mosquito repellents applied to the skin.
Experimental Design The experimental design will involve deploying commercial essential oil diffusers together with mosquito traps in staff and student areas of selected buildings on the Callaghan campus during peak mosquito breeding season (October – February).
The primary dependent measures will be mosquito counts within each trap as well as brief consumer acceptance, preference and mosquito annoyance measures that are completed online by volunteer staff and students who frequent the experimental sites.
After establishing a 3 day baseline (no scent) the diffusers will be charged with the essential oil of one of the four randomly selected Eucalyptus species (simulated for E.Macathurii). Oils from the four species will be delivered for three days interspersed with 3 day periods of no scent. After each 6 day cycle a different scent will be randomly selected for each site. For each site volunteers staff will be encouraged to use and record their use of personal (skin applied) mosquito repellent during randomly selected no scent 3 day periods.
Data Analysis To test the three hypothesis multivariate time series analysis will be used where modelling is based on the 6 independent variables (ie. the four essential oils, the no scent periods and the personal insect repellent periods). These analysis will be applied to the dependent measures, mosquito trap counts and consumer acceptance, preference and mosquito annoyance.
Budget 6 sites will be selected for this study with the primary costs being Essential Oil diffuser rental and installation (6 x $150 x 3 months = $2700), Mosquito Traps, (18 x $50 = $900), (Essential Oils, Solvents, additives and sundry supplies = $1400). Total Budget = $5000.