Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2004
Publication Date: 9/1/2004
Citation: Giblin-Davis, R., Center, B.J., Davies, K.A., Purcell, M., Scheffer, S.J., Taylor, G.S., Goolsby, J., Center, T.D. 2004. HISTOLOGICAL COMPARISONS OF FERGUSOBIA/FERGUSONINA-INDUCED GALLS ON DIFFERENT MYRTACEOUS HOSTS1. Journal of Nematology. 36:249-262.2004b. Interpretive Summary: Melaleuca quinquenervia, or paperbark tree, was introduced to south Florida in the early 1900s for use as an ornamental plant. It has proliferated tremendously since then and forms dense stands of large trees that are of little use to wildlife. It is invading wetlands at a rapid rate and is displacing native vegetation and wildlife in the process. Being explosively flammable, it presents an extreme fire hazards to houses and other building located near these dense stands and it invades pasturelands reducing forage value. As part of an ongoing project to develop biological control agents, the fly Fergsonina sp. was studied in Australia. This fly might help control Melaleuca by destroying the bud tissues that form new shoots or flowers, but to ascertain its safety, its life history must first be understood. The fly carries a nematode that it deposits in the buds of the tree when it lays an egg. The nematode causes the bud to deform and produce extra tissue, called a gall, that the fly larva eats. The gall usurps nutrients that the plant would otherwise use to grow or to produce seed, so when numerous galls are present the plant can't function normally. Other plants related to melaleuca also serve as hosts, but each plant has its own unique species of each fly and its nematode partner. This system has recently been rediscovered and it has been found that each plant produces a unique type of gall. The galls from different plant species have been characterized based on histological comparisons.
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 members of the Leptospermoideae (six species of Eucalyptus, two species of Corymbia, and seven species of broad-leaved Melaleuca) native to Australia, sectioned, and histologically examined to assess the effects of parasitism. 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 formation in all four types appeared to be due to the location and timing of placement of the nematodes and fly eggs 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, each, with an enlarged nucleus, nucleolus, and granular cytoplasm that resembled shoot bud gall cells induced by nematodes in the Anguinidae.