Induction and Formation of Pouch and Emergence Galls in Eucalyptus pulchella Leaves

Abstract

Two types of leaf galls were found on three Eucalyptus species (E. pulchella, E. obliqua and E. regnans) infested with an undescribed species of psyllid (Psyllidae: Homoptera) and eriophyid mites (Acadicrus and Rhombacus spp.) (Eriophyidae: Prostigmata). Abnormal cellular activity resulting in gall formation was most probably associated with the lowering of epidermal permeability to air by the physical presence of feeding psyllid nymphs and their excreta. The eriophyid mites opportunistically exploited the resultant gall tissue but were not involved in its formation. In one possible mechanism of gall formation it is envisaged that localized changes in the amounts of auxin-like substances are involved and that such changes are related to reductions in leaf diffusion. Similar leaf deformities were artificially induced on E. pulchella and a number of other Eucalyptus species. The subgenus Monocalyptus was the most sensitive to the applied treatments and the majority of gall-forming psyllids occur in this subgenus.