On the Relative Abundance of Some Australian Psyllidae That Coexist on Eucalyptus Blakelyi.

Abstract

A 7-year study of fluctuations in the numbers of four psyllids, Glycaspis spp. (G. brimblecombei and G. prepta combined), Spondyliaspis sp. and Creiis costatus, on mature E. blakelyi in the woodlands of the Australian Capital Territory suggests that: (I) The favourableness of the leaves of the host plant as a source of food was the principal environ- mental influence affecting the abundance of each kind of psyllid; (2) Favourableness was determined by the depIetion and aging of leaves involved in the host plant's 2-year cycle of reproduction and foliage replacement (notably, as affected by the extent of fruit production), and, to differing degrees for the different kinds of psyllid, by the extent of damage caused by leaf-eating beetles, previous and prevailing soil moisture conditions (as estimated by a model using rainfall and evaporation as input), and possibly air temperatures in autumn and winter ; (3) The resulting variation in the favourableness of leaves was responsible for similarities in the fluctuations of abundance recorded for the psyllids; and (4) Those characteristics of the psyllids which defined their food requirements and ability to obtain food were responsible for differences in their abundance, mainly in the amplitude of fluctuations.