Interactions between geckos, honeydew scale insects and host plants revealed on islands in northern New Zealand, following eradication of introduced rats and rabbits

Invasive species that reach islands can have effects that ripple through communities. As a corollary, once invasive species are removed, the responses by resident species may also have ripple effects, sometimes with outcomes that are unpredicted. One such unpredicted response is reported on islands off north-eastern New Zealand following the removal of rabbits (Oryctolagus cuniculus) and Pacific rats or kiore (Rattus exulans. As composition of the vegetation changed and geckos became increasingly abundant, a source of energy for the geckos was revealed: honeydew produced by the scale insect Coelostomidia zealandica (Hemiptera: Margarodidae) infesting ngaio (Myoporum laetum) and karo (Pittosporum crassifolium. Honeydew may have significant effects on the carrying capacity of invertebrates and birds in mainland forests of New Zealand. However, its importance for geckos on islands was apparently masked by reduced gecko abundance in the presence of introduced predators, and suppression of host plants by introduced herbivores. Possible mechanisms of spread and new hosts of C. zealandica are described, and the vulnerability of the scale insect on islands with introduced mammals that suppress recruitment of selected host species is emphasised.

Author Towns, D. R.
Year 2002
Publisher International Conference on Eradication of Island
Region NZ