BACKGROUND Insects rely on their sense of smell to locate food and hosts, find mates and select sites for laying eggs. Use of volatile compounds, such as essential oils (EOs), to repel insect pests and disrupt their olfaction‐driven behaviors has great practical significance in integrated pest management. However, our knowledge on the olfaction‐based mechanisms of EO repellency is quite limited. RESULTS We evaluated the repellency of peppermint oil and nine plant EO components in Drosophila melanogaster, a model insect for olfaction study, and D. suzukii, a major fruit crop pest. All nine volatiles, menthone, (−)‐menthol, menthyl acetate, (R)‐(+)‐limonene, nerol, (+)‐fenchone, (−)‐α‐thujone, camphor, norcamphor and peppermint oil, elicited repellency in D. melanogaster in a dose‐dependent manner. Most of the compounds, except camphor, also elicited repellency in D. suzukii. Menthone, (R)‐(+)‐limonene and (+)‐fenchone were the most potent repellents against D. suzukii. Repellency was reduced or abolished in two D. melanogaster mutants of the odorant receptor co‐receptor (Orco), indicating that the observed repellency is odorant receptor (Or)‐mediated. Repellency by peppermint oil, menthone, (R)‐(+)‐limonene, (−)‐α‐thujone and norcamphor also involves Or‐independent mechanism(s). Single sensillum recording from both species revealed that common and distinct Ors and olfactory receptor neurons were activated by these compounds. CONCLUSIONS The tested plant EO components evoke repellency by activating multiple Ors in both Drosophila species. Our study provides a foundation for further elucidation of the mechanism of EOs repellency and species‐specific olfactory adaptations. © 2021 Society of Chemical Industry

Isatin is an endogenous indole compound in humans and rodents that has a wide range of biological activity. In rat models, isatin concentrations have been shown to increase in the heart, brain, blood plasma, and urine with stress. Studies on patients suffering from Parkinson's disease have indicated a correlation between progress of the disease and urinary output of the molecule. Isatin is electrochemically active and can therefore be detected with electrochemical techniques. In this work, we compared the performance of a nitrogen‐incorporated tetrahedral amorphous carbon (ta‐C:N) and a boron‐doped nanocrystalline diamond thin‐film electrode for the oxidative detection of this biomolecule using flow injection analysis with amperometric detection. The measurements were performed in 0.1 phosphate buffer pH 7.2. The ta‐C:N electrode, like boron‐doped nanocrystalline diamond, exhibits some excellent properties for electroanalytical measurements including (i) low background current and noise, (ii) microstructural stability at positive detection potentials, and (iii) good activity for a wide range of bioanalytes without conventional surface pretreatment. The results reveal that both electrodes exhibit a linear dynamic range from 100 to 0.1 μmol L−1, a short‐term response variability 3–4 % RSD (30 injections), a sensitivity of 18 mA M‐1, and a limit of detection (S/N=3) of 1.0×10−7 mol L−1 (14 ng mL−1 or 2.5 fmol).

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