Fergusonina spp.
(Diptera: Fergusoninidae)

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There is only one genus of true flies reported to interfere with planted trees in Papua New Guinea. It is Fergusonina spp. (Fergusoninidae), forming leaf and flower galls on several species of Eucalyptus. Fergusonina is a minor pest in PNG inhibiting the flower and seed production of the host. Little is known about the biology of this species, however closely related Australian relatives have probably a very similar and definitely a very interesting biology. The flies have a complex life cycle including the symbiotic association with a nematode of the genus Fergusobia. A fertilised female nematode enters the body cavity of a female fly larva in the gall. The hatched larval nematodes enter the oviduct of the female fly and are carried out of the gall, when the fly emerges. After mating the nematodes are passed out together with the fly eggs, when these are laid into Eucalyptus flower buds. There, the nematodes develop together with the flies inside the induced gall. The chemical that induces the gall is produced by the nematode, therefore the apparently parasitic interaction is of mutualistic nature, hence for the advantage of Fergusonina. Interestingly, a natural enemy of Fergusonina is the gall-forming wasp Megastigmus spp. (Torymidae). Even though being another pest species of Eucalyptus the wasp effectively competes with the fly for suitable flowers to lay eggs, resulting in the death of large numbers of Fergusonina.

Fergusonina sp.
(source unknown)

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Michael F. Schneider, 1999