Interactive association between Puccinia psidii and Oxyops vitiosa, two introduced natural enemies of Melaleuca quinquenervia in Florida

The Neotropical rust fungus Puccinia psidii and the Australian weevil Oxyops vitiosa are introduced natural enemies of Melaleuca quinquenervia (melaleuca) in south Florida. Both organisms exploit expanding leaves so we sought to investigate the interactions among these natural enemies and their shared host plant melaleuca. Olfactory-response studies showed that the leaves not infected with rust attracted more female weevils. Similarly, adults and late instars consumed higher proportions of rust-free versus rust-diseased leaf tissues in dual-choice tests, while early instars showed no preference. Female weevils preferentially oviposited on rust-free leaves but similar proportions of eggs hatched on either leaf type. No-choice feeding trials on excised leaves showed increased rust-pustule coverage to cause concomitant decreases in larval survivorship. Most larval mortality occurred as 1st and 2nd instars when fed with leaf tissues having ⩾50% rust-pustule coverage. Similar trials with whole plants caused lower larval survival on rust-diseased versus rust-free leaves, with greater prepupal weights realized on rust-free leaves. Herbivory on intact plants by O. vitiosa reduced rust-susceptible tissues and rust-pustule densities under both controlled and ambient environmental conditions. These data suggest that P. psidii and O. vitiosa influence each other's life cycle and possibly antagonize each other's effects as biological control agents of M. quinquenervia because both agents compete for newly expanding foliar tissues for colonization, reproduction, and survival during their early stages of development.