Chemical composition, toxicity, and repellence of plant essential oils against Diaphorina citri (Hemiptera: Liviidae)

Diaphorina citri Kuwayama (Hemiptera: Liviidae) is an invasive species in America and is the main vector of the pathogen associated with Huanglongbing, a deadly disease of citrus plants in the world. The management of such a problem includes the intensive use of insecticides to reduce vector populations and risk of pathogen transmission. As an alternative to synthetic insecticides to control D. citri, the present study determined the chemical composition of diverse plant essential oils and assessed the toxicity and repellency of oil extracts against D. citri. Their chemical composition and abundance were determined by gas chromatography coupled to mass spectrometry. Adults and nymphs were exposed to leaf citrus discs treated by spraying or immersion with different oil extract concentrations. Repellency was assessed by exposing adults to treated leaves in experimental arenas and determining the number of insects remaining on the leaf after different time periods compared with the control. The main oil compounds in the tested plants were anethole, verbenone, 4-ethyl-4-methyl-1-hexene, 4-allylanisole, and trans-tagetone. Oils from Rosmarinus officinalis L. and Schinus molle L. caused no repellent or insecticide effects on D. citri. In contrast, oil extracts from the Foeniculum vulgare Mill. and Tagetes species were toxic and/or repellent for both adults and nymphs. There was a positive relationship between toxicity and concentration. Oil extracts from Tagetes lucida, T. coronopifolia, and T. terniflora were repellent (> 92%) at 40 mg mL^-1; this was correlated with the concentration and decreased over time. Essential oils extracts from the Tagetes species could represent a potential defense that could be integrated into the management of D. citri.