EAG responses to host-based attractants and temporal patterns in host-seeking flight of Xyleborus glabratus, X. affinis, and X. ferrugineus

The redbay ambrosia beetle, Xyleborus glabratus Eichhoff, is an exotic wood-boring insect that vectors the mycopathogen responsible for laurel wilt, a lethal vascular disease of trees in the Lauraceae, including avocado (Persea americana Mill.).  Effective semiochemical-based detection and control programs for X. glabratus will require an understanding of the chemical ecology and host-seeking behaviors of this new invasive pest.  This study (1) presents an electroantennography (EAG) method developed for assessment of olfactory responses in ambrosia beetles; (2) uses that new method to quantify EAG responses of X. glabratus, X. affinis, and X. ferrugineus to volatiles from three host-based attractants:  manuka oil (essential oil extract from Leptospermum scoparium Forst. & Forst.), phoebe oil (extract from Phoebe porosa Mex.), and wood from silkbay (Persea humilis Nash); and (3) documents temporal differences in host-seeking flight of the sympatric Xyleborus species.  Field observations revealed that X. glabratus engages in flight several hours earlier than X. affinis and X. ferrugineus, providing a window for selective capture of the target pest species.  In EAG analyses with X. glabratus, antennal response to phoebe oil was equivalent to response to host Persea wood, but EAG response elicited with manuka oil was significantly less.  In comparative studies, EAG response of X. glabratus was significantly higher than response of either X. affinis or X. ferrugineus to all three host-based substrates.  Future research will use this EAG method to evaluate olfactory responses to synthetic terpenoids, facilitating identification of the specific kairomones used by X. glabratus for host location.