THE RAPID SUPPRESSION OF THE GROWTH OF MELALEUCA-QUINQUENERVIA SAPLINGS IN AUSTRALIA BY INSECTS

Melaleuca, Melaleuca quinquenervia (Cav.) S. T. Blake, populations in Florida are quite different in appearance from those observed in Austr alia, its native home. In Florida, where melaleuca is an introduced we ed, the trees are generally taller, straighter, and form very dense po pulations. Sixty small (approx. 0.5 m) saplings were grown in pots bes ide our shadehouse in Townsville, Australia, in order to determine the role which Australia's herbivorous insects may play in limiting the g rowth of melaleuca. Half of these were treated every fortnight with sy stemic insecticides, which limit (but do not entirely prevent) insect damage to the saplings. Sapling growth was regularly monitored, as was insect presence and damage. After just 84 days, insecticide treated s aplings were significantly taller than their unsprayed counterparts. T he trunk girth and diameter of the sprayed saplings became significant ly broader after 147 and 161 days respectively. Harvesting of 20 of th e saplings after six months, revealed that the insecticide treated sap lings had greater stem biomass. During the initial six months of this study, the greatest damage to the untreated trees seems to have been t he tip-wilting caused by Pomponatius typicus (Heteroptera: Coreidae) a nd the death of young leaves resulting from the feeding activities of Apion sp. B (Coleoptera: Apionidae). Our finding that ambient, low-lev els of insect herbivores can rapidly suppress the growth of a large wo ody tree species is discussed with respect to the prospects for biolog ical control of melaleuca.