Insects and a pathogen suppress Melaleuca quinquenervia cut-stump regrowth in Florida

Authors: Rayamajhi, Min; Pratt, Paul; Center, Ted; VAN, THAI

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2009
Publication Date: 8/3/2009
Citation: Rayamajhi, M.B., Pratt, P.D., Center, T.D., Van, T.K. 2009. Insects and a pathogen suppress Melaleuca quinquenervia cut-stump regrowth in Florida. Biological Control. 53:1-8.2010. DOI information: 10.1016/j.biocontrol.2009.07.017.

Interpretive Summary: Use of several types of natural enemies to control weedy plants has often been proposed. We assumed that when we allow multiple natural enemies, such as insects and fungi to attack weedy plants, the amount of damage on the plants will be much more severe compared to those caused by the same natural enemies when they are allowed to attack the plants separately. To test this assumption we released two types of insects (a weevil that feeds on leaf tissue and a psyllid that feeds on leaf sap) and a rust-colored fungus separately as well as together on the coppices growing on the melaleuca stumps. We harvested these coppices annually and evaluated them to document their impact in terms of cut-stump and coppice damage and death. Insect, fungus and the simultaneous use of insects and fungus caused higher level of damage and mortality of cut-stumps and coppices when compared to those in control treatments in which the cut-stump coppices were protected from insect and fungal attack by regular spray of systemic insecticide and or fungicide. The stumps and coppice damage and mortality were remarkably higher when both insects and rust-fungus were allowed to simultaneously attack the same coppices.

Technical Abstract: Utilization of multiple natural enemy species in weed biocontrol programs has often been advocated. Herein, we tested the hypothesis that multiple guilds of natural enemies, rather than individual species, would result in greater levels of damage to target host plants. This was investigated by evaluating the herbivorous insects Oxyops vitiosa (weevil) and Boreioglycaspis melaleucae (psyllid) and a rust-fungus Puccinia psidii separately and together when attacking cut-stump coppices of the invasive tree Melaleuca quinquenervia (melaleuca). We felled 120 trees in each of three mature melaleuca stands and assigned coppicing stumps to one of the four treatments: control (insects and rust-fungus excluded); insect (O. vitiosa and B. melaleucae) herbivory; rust-fungus (P. Psidii) inoculation; and integration of insects and rust-fungus. We repeated the experiment once in adjacent plots of the same stands as above. Coppices on the stumps were harvested annually for three years and evaluated for damage, height, branching, mortality and biomass. Three treatments: insects, rust-fungus, and their integrated treatments produced higher levels of coppice damage and mortality compared to controls; these three treatments also effective in reducing plant height, branching and biomass of surviving coppices. These impacts of insects and rust-fungus integration treatment were synergistic on coppice-damage while additive on stem morality, and reduction in height, branching, leaf biomass and total biomass of coppices. Rust-fungus and psyllid showed better ability to co-attack same leaf tissues compared to rust-fungus and weevil. Overall effects of the three natural enemies led to markedly reduced performance of the perennial invasive tree.