Electroantennographic responses of the Asian citrus psyllid to citrus volatiles

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae) constitutes a singular and daunting challenge to citrus worldwide because it transmits citrus greening disease, Candidatus Liberibacter asiaticus, also known as huanglongbing disease (HLB) for which there is no cure. Recent effort seeks to identify volatile compounds of insect or plant origin for monitoring and trapping. Small antennal responses were reported from electroantennogram (EAG) tests to (+)-limonene and grapefruit volatiles. Other than (+)-limonene, no compound capable of eliciting antennal response in D. citri has been identified. A multitude of volatile compounds is released by healthy citrus tissue and tissue disrupted by mechanical damage or exposure to chemical elicitors. The fate of these compounds in the atmosphere and the ecological role of breakdown products represent a poorly known aspect of plant-herbivore interactions. Degradation of host plant volatiles may result in production of foraging cues that are overlooked because they do not appear in the host plant itself.  Here we report results of gas chromatograph-coupled electroantennogram (GC-EAD) studies from D. citri, identification of active and inactive compounds from collections of citrus volatiles, and the serendipitous discovery of degradation products from common citrus volatiles that are active by EAG, GC-EAD and olfactometer assays.