Psyllid responses to colored sticky traps and the colors of juvenile and adult leaves of the heteroblastic host plant Eucalyptus globulus

Heteroblasty describes plants with juvenile and adult vegetative shoots that differ morphologically. Virtually nothing is known about the affects of this source of within-plant variation on host-plant selection by herbivorous insects. This is the first study on the use of visual cues by insects that specialize on different shoot types of a heteroblastic plant. Two psyllid species (Ctenarytaina eucalypti Maskell and C. spatulata Taylor) specialize on glaucous juvenile and glossy adult shoots of Eucalyptus globulus Labill., respectively. We compared their responses to artificial colors and to the colors of expanding and expanded juvenile versus adult leaves. Sticky traps were used to compare psyllid response to seven artificial colors. A "color tube" was developed to compare psyllid responses to leaf color. Both psyllid species preferred yellow traps over all other colors (red, blue, green, white, and clear), and color preference was independent of species. Both species were also more attracted to the colors of expanding and expanded juvenile leaves than to adult leaves. Although the psyllids perceived differences between the colors of juvenile and adult leaves of E. globulus, their responses suggest that leaf color alone is not the basis of discrimination between foliage types.