Development of chitosan encapsulated thyme essential oil as an alternative fruit fly repellent for household use

Fruit flies not only cause unsightly scenes, but also carry food borne pathogens that can pose
severe health risks. They are common in food service facilities, and can also infest regular
households, particularly when a family composts food waste. Although these small pests are a
nuisance, there is still no established ready-to-use method to control fruit fly infestations at
home, and most people resort to using homemade fly traps from everyday items such as vinegar
and dish soap. To address this issue, in this study, a thyme oil encapsulating chitosan product was
developed so that it can be used in household compost bins to help control fruit fly infestations
through the repelling and killing of fruit flies. The experiment was conducted in two steps. First,
a 2-choice fruit fly repelling assay was established and 18 different essential oils were selected
through literature research for reported insect repelling effect and tested in the assay. A separate
toxicity assay was also conducted through recording the number of fruit flies killed by the
essential oil. Thyme oil was selected for further experimental design because it showed the
highest repelling effect, and it is safe and environmentally friendly for home-use. Second, to
prevent fast depletion and reduce the need for repeated application, the thyme oil was
encapsulated into a chitosan matrix for controlled release. Chitosan was selected due to its
biodegradability and unique property of turning into semi-solid form through ionization gelation.
After testing different experimental conditions of encapsulated thyme oil concentration, type of
surfactant, and surfactant concentration for optimal encapsulation efficiency and loading
capacity, a prototype product was generated using 2% chitosan, 2% thyme oil and 1% Tween 80.

The prototype demonstrated 100% fruit fly repelling effect and 65% fruit fly killing effect after
24 hours in the 2-choice repelling assay and the toxicity assay, respectively. Encapsulation
efficiency and loading capacity, measured by thyme oil absorbance at 270 nm, were 65.1±3.5%
and 61.2±3.3%, respectively. No significant loss of thyme oil content or insect repelling
capability was observed after six weeks. This study created a prototype product suitable for
household use to help control fruit fly infestations and may provide useful information to guide
encapsulation of a wider range of pesticides to replace insect sprays that are of very short effect
duration. Further studies will be conducted to determine the long term stability of the product,
and more materials (e.g., other natural polymers such as agar, gelatin, and alginate) will be
investigated to determine the optimal encapsulation with affordable price and promising fruit fly
repelling efficiency.