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

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 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 6–13 coppicing stumps to each of the four treatments: control (insects and rust fungus excluded); insect herbivory; rust-fungus-infection; and combination of insect herbivory and rust fungus infection. We repeated the experiment once in adjacent plots located within the same stands as above. Coppices were harvested annually for three years and evaluated for damage, height, branching, mortality, and biomass. Three treatments: insects, rust fungus, and their combination caused higher levels of coppice damage and mortality compared to controls; these three treatments also reduced plant height, branching, and biomass of surviving coppices. These impacts of insects and rust-fungus-combination were additive on cut-stump and coppice stem mortality, and reduction in height, branching, leaf biomass, and total biomass of coppices. The rust fungus and psyllid showed better ability to co-attack the same leaf tissues compared to the rust fungus and the weevil. In conclusion, overall effects of the three natural enemies led to markedly reduced performance of the invasive tree melaleuca.