The nymphal stage of Cardiaspina densitexta (Homoptera : Psyllidae) on leaves of Eucalyptus fasciculosa

Abstract

First-instar nymphs of C. densitexta crawl freely from leaf to leaf on the plant, tending to disperse from overcrowded leaves; some are carried from one tree to another by wind. The lower side of the basal end of mature leaves is the favoured site for settling. Survival and rate of growth in both winter and summer are greater on the north than on the south side of trees. In the laboratory, nymphs can be successfully reared on disks cut from E, fasciculosa leaves and floated on distilled water. Under high light intensity the initial favourability of sun leaves over shade leaves is quickly lost, but disks from old leaves continue to be less favourable than those from mature leaves. Mortality is much greater on leaf tissue exposed to dim light, and disks of sun leaves are then less favourable than those of shade leaves. Isolated individual nymphs have a lower chance of survival and grow more slowly than when there are several nymphs in close proximity. The feeding of nymphs causes discoloration and eventual death of the leaf tissue immediately surrounding the feeding site, and there is, possibly, a secondary systemic toxic effect on the host. These results seem to support the hypothesis that the phloem sap of the host plant-and specifically its soluble nitrogen content is, for most of the time, an inadequate source of food for the nymphs.