Antennal and behavioral response of the Asian citrus psyllid (Diaphorina citri Kuwayama) to degradation products of citrus volatiles

Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae) vectors the bacterial causal pathogen of the deadly citrus disease, Huanglongbing (Citrus greening) which is a major threat to citrus industry worldwide. We studied antennal and behavioral responses to principal components of headspace volatiles collected from citrus flush. Candidate compounds identified by GC-EAD were confirmed by EAG of neat compounds loaded into glass stimulus tubes. Tubes loaded with β-ocimene or citral produced no responses immediately after preparation at a range of concentrations. The same tubes became stimulatory after 3 to 9 days at room temperature, apparently through oxidative degradation. GC-MS demonstrated that both compounds degraded completely over 3 to 9 days in glass (with or without filter paper) to acetaldehyde, acetone, acetic acid, formic acid and other compounds. GC-EAD of extracts of filter paper loaded with neat compounds aged 3 to 9 days in glass pipettes identified peaks that elicit consistent and large antennal responses and determined by GC-MS to be acetic and formic acids. Both were highly stimulatory to D. citri antennae and positively correlated with log dose. Probing behavior of D. citri was studied by incorporating blends of antenally active compounds in varying proportions and amounts into an emulsified wax substrate (SPLAT ^TM, ISCA technologies, Inc). More probes were observed on SPLAT containing blends of acetic and formic acids compared with either acid separately or other compounds. Our study suggests that phytophagous insects may use degradation products for host finding and that the Asian citrus psyllid may orient to formic and acetic acid present in the citrus tree canopy. These observations of antennally active compounds, both constitutive and arising as degradation products from constitutive plant volatiles, may contribute to the development of attractants and/or repellants for this important psyllid species.