Repellency and toxicity of plant‐based essential oils and their constituents against Diaphorina citri Kuwayama (Hemiptera: Psyllidae)

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Abstract
The Asian citrus psyllid, Diaphorina citri Kuwayama, vectors Candidatus Liberibacter asiaticus (Las), the presumed causal agent of huanglongbing. D. citri generally rely on olfaction and vision for detection of host cues. Certain plant volatiles and plant‐derived essential oil products are known to repel several arthropod species and are considered minimum‐risk pesticides. We examined the effect of five essential oils and eight chemicals previously reported to have activity against various insect species on D. citri behaviour in a two‐port divided T‐olfactometer in an effort to identify repellents for further consideration and testing as crop protectants for D. citi. Volatiles from essential oils of coriander, lavender, rose, thyme, tea tree oil and 2‐undecanone, a major constituent of rue oil repelled D. citri adults compared with clean air. Also, coriander, lavender, rose and thyme oil inhibited the response of D. citri when co‐presented with citrus leaves. Volatiles from eugenol, eucalyptol, carvacrol, β‐caryophyllene, α‐pinene, α‐gurjunene and linalool did not repel D. citri adults compared with clean air. In an effort to isolate the repellents and toxicants from effective essential oils, the headspace components of coriander and lavender oil were analysed by gas chromatography‐mass spectrometry and revealed that α‐pinene and linalool were the primary volatiles present in coriander oil while linalool and linalyl acetate were the primary volatiles present in lavender oil. Coriander, lavender and garlic chive oils were also highly toxic to D. citri when evaluated as contact action insecticides using a topical application technique. The LC50 values for these three oils ranged between 0.16 and 0.25 μg/D. citri adult while LC50 values for rose and thyme oil ranged between 2.45 and 17.26 μg/insect.

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