Not Led by the Nose: Volatiles from Undamaged Hosts Do Not Influence Psyllid Orientation.

Psyllids (Hemiptera: Psylloidea) are small sucking insects with high host plant specificity. Despite the primitive olfactory system of psyllids, some species have been suggested to rely on host plant volatiles (HPVs) for seasonal migration between summer deciduous hosts and winter coniferous hosts. Similarly, enhanced attraction of psyllid vectors has been observed as a result of the manipulation of host odors by plant pathogens. As yet, there are no studies of olfaction in psyllids that utilize evergreen eucalypt hosts. We investigated the behavioral responses of adults of four -feeding psyllids-, , and -to their respective HPVs in Y-tube olfactometer bioassays. We also used existing physiological data for to investigate potential olfactory tuning that may modulate the preference for morphologically juvenile leaves over morphologically adult leaves. Although adult were consistently repelled by HPVs from damaged host leaves, none of the species exhibited positive chemotaxis to HPVs from undamaged leaves. Surprisingly, was repelled by HPVs from undamaged host leaves. Our findings provide little support for a significant role of olfaction in host location by -feeding psyllids. We propose a number of ecological hypotheses to explain these unexpected findings.