Submitted to: Journal of Nematology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/13/2004
Publication Date: 12/13/2004
Citation: Giblin-Davis, R.M., Center, B.J., Davies, K.A., Purcell, M.F., Scheffer, S.J., Taylor, G.S., Goolsby, J., Center, T.D. Histological comparisons of fergusobia/fergusonina-induced galls on different myrtaceous hosts.. Journal of Nematology. 2004:36:249-262. Interpretive Summary: The Australian paperbark tree, Melaleuca quinquenervia, is highly invasive in the wetlands of Florida. Populations of this weedy tree currently occupy more than 500,000 acres, constituting a considerable threat to the Florida Everglades. Federal and State agencies are working to develop various methods of controlling this invasive plant. Some efforts have involved identifying insect species that feed on this plant in its native range in Australia in order to identify those that might be suitable for release in Florida as biological control agents. A galling fly was identified as a potential biological control agent, but the biology of this species and its close relative was poorly known. This study investigates the biology of galling flies by looking at the structure of the galls formed on different host plants. This information will be of interest to Federal and State agencies interested in the control of invasive paperbark tree populations. This information will also be of interest to entomologists and evolutionary biologists.
Technical Abstract: The mutualism between different host-specific Fergusobia nematodes and Fergusonina flies is manifested in a variety of gall types involving shoot or inflorescence buds, individual flower buds, stems, or young leaves in the plant family Myrtaceae. Different types of galls in the early to middle stages of development, with host-specific species of Fergusobia/Fergusonina, were collected from Australian members of the subfamily Leptospermoideae (six species of Eucalyptus, two species of Corymbia, and seven species of broad-leaved Melaleuca). Galls were sectioned and histologically examined to assess morphological changes induced by nematode/fly mutualism. The different gall forms were characterized into four broad categories; 1) individual flower bud, 2) terminal and axial bud, 3) 'basal rosette' stem, and 4) flat leaf. Gall morphology in all four types appeared to result from species-specific selection of the oviposition site and timing and number of eggs deposited in a particular plant host. In all cases, early parasitism by Fergusobia/Fergusonina involved several layers of uninucleate hypertrophied cells lining the lumen of each locule (gall chamber where each fly larva and accompanying nematodes develop). Hypertrophied cells in galls were larger than normal epidermal cells, and each had an enlarged nucleus, nucleolus, and granular cytoplasm that resembled shoot bud gall cells induced by nematodes in the Anguinidae.