SCALE INSECTS CONSISTENTLY AFFECT ROOTS MORE THAN SHOOTS - THE IMPACTOF INFESTATION SIZE ON GROWTH OF EUCALYPT SEEDLINGS

1 Different infestation levels of the phloem-feeding scale insect, Eri ococcus coriaceus Maskell (Hemiptera: Eriococcidae), consistently redu ced root growth more than shoot growth in seedlings of Eucalyptus blak elyi Maiden (Myrtaceae).2 Low levels of scale insect infestation signi ficantly decreased root and lignotuber biomass but not shoot biomass. High levels of infestation , however, adversely affected all plant par ts. Root and lignotuber biomass declined linearly, while the responses of stem and leaf biomass were nonlinear, with respect to increasing t otal insect load. 3 Plant responses to scale insect infestations may b e explained by considering sap-sucking insects as additional sinks tha t compete against plant sinks and both redirect and drain resources fr om the plant. 4 Scale insect populations exhibited strong density depe ndent effects, suggesting they were severely depleting resources withi n their hosts. Extensive shoot death at high levels of infestation may have contributed to insect population decline by causing scale insect s to die prematurely or by reducing the availability of suitable feedi ng sites.