Biological Control of Melaleuca
The biological control method uses the tree's natural enemies to keep the trees in check. Two biological control agents, both insects, are currently at work on melaleuca, and they are particularly fond of young seedlings and new leaves. Feeding damage from these two insects is reducing melaleuca reproduction, seedling establishment, and growth. You can order biological control insects to release on your property.
The two biological agents released and established thus far are the melaleuca weevil (Oxyops vitosa) and the melaleuca psyllid (Boreioglycaspis melaleucae). A third agent, the melaleuca bud-gall fly (Fergusonina turneri), has been released but a population has not yet established in the field. Another potential agent, the stem-gall fly (Lophodiplosis trifida) is still being studied for possible future release.
The melaleuca weevil was released in 1997. It has been successful in establishing itself, dispersing from the release site, and eating melaleuca. The immatures, or larvae, feed only on new leaf (young) tissue. Adults prefer new leaves, but will eat mature leaves. One shortcoming of this particular insect is that it requires dry soil for the larvae to pupate. Melaleuca commonly occurs in standing water, and the weevils cannot complete their life cycle from these particular trees.
Weevil larvae scrape off the living plant tissue from the leaves, and leave behind the waxy cuticle--these feeding scars look like little "windows" on the leaves. Oval-shaped holes in the leaves are evidence of adult weevil feeding.
The melaleuca psyllid was released in 2002. Like the weevil, the psyllid is well-established and widely dispersed across South Florida. Unlike the weevil, the psyllid spends its entire life cycle in the tree so water levels are not a problem for it. In fact, in some areas psyllid populations are doing so well that they are even killing small saplings.
Immature psyllids, or nymphs, are readily detected due to the presence of flocculence--a white, waxy substance secreted by the nymphs that may deter attacks from predators. Adult psyllids are very small (about the size of a gnat). Besides some death of small trees, the psyllids are reducing flowering and seed production, thinning the tree canopy, and stunting tree growth.
Limited releases of the melaleuca bud-gall fly were made in the spring of 2005 but the insects do not appear to have survived. Currently more flies are being reared and release techniques refined in preparation for releases in the winter of 2006-2007. This particular insect produces galls on melaleuca buds that preempt flower and seed production and drain plant resources. For more information about this species, read the March 2004 issue of Offshoots.
The stem gall-fly is still undergoing host-specificity testing (ensuring it will only eat melaleuca) in a quarantine lab in Gainesville, FL. No release dates are yet projected.
For pictures of these insects, check out the photo gallery.
melaleuca psyllid (Boreioglycaspis melaleucae)