Leaf surface traits may influence host specificity in psyllids of Eucalyptus, Spondyliaspis cf. plicatuloides (Froggatt) and Glycaspis brimblecombei Moore (Hemiptera: Aphalaridae)

Spondyliaspis cf. plicatuloides and Glycaspis brimblecombei (Hemiptera: Aphalaridae) are invasive insect pests of Eucalyptus, native to Australia. The insects feed on eucalypt sap, and both psyllid species exhibit clear preferences for different species and hybrids of Eucalyptus. The objective of this study was to identify the constitutive morphological and phytochemical characteristics underlying these host preferences. Four preferred and eight non-preferred eucalypt hosts were selected for evaluation. Thirteen leaf morphological features of the 12 eucalypts were analysed. The non-polar and polar metabolites in and on the surface of leaves of each eucalypt species were extracted, and their chemical composition was analysed using gas chromatography coupled with mass spectrometry. The leaf volatile profiles of hosts and non-hosts of S. cf. plicatuloides and G. brimblecombei did not differ sufficiently to explain the host choices of the two eucalypt psyllids. The leaf polar metabolite profiles of the susceptible hosts of the two psyllids differed significantly but did not explain the host preferences of the two psyllid species. However, preferred hosts of S. cf. plicatuloides and G. brimblecombei had some leaf morphological features and wax metabolites in common. Our results show that particular combinations of leaf morphological features and wax metabolites might influence the host choice of eucalypt-feeding lerp psyllids, but no traits explaining the differences in host-selection behaviour between S. cf. plicatuloides and G. brimblecombei were identified.