Successive replacement of tending ant species at aggregations of scale insects (Hemiptera: Margarodidae and Eriococcidae) on Eucalyptus in south-east Queensland

Scale insects generally display enhanced survival rates in the presence of tending ants, but studies of ant and scale–insect interactions typically examine a single tending ant species. This study investigated the successive changes in tending ant species during the lifespan of two species of scale aggregations, a monophlebuline margarodid and an Eriococcus sp. (Eriococcidae) on the Plunkett mallee, Eucalyptus curtisii . Scale aggregations were also subject to an ant-exclusion experiment to quantify the degree to which ants increased the survival rates of both scale insect species. Tending ants assorted to two categories, dominant and secondary, with a significant bias according to the chronological age of the scale aggregation. Secondary ant species (opportunists and subordinates) tended juvenile-scale aggregations. These were replaced by a dominant species of Iridomyrmex (Dolichoderinae), which almost exclusively tended larger (mature) aggregations until the senescent stages of the infestation when secondary ant species returned. Exclusion of the primary tending Iridomyrmex ant increased mortality of both species of scale insects by 96% relative to controls.