Galling problems – the Fergusobia nematode/Fergusonina fly mutualism on myrtaceous hosts

Fergusobia (Sphaerularioidea, Tylenchida) is the only known nematode to have a dicyclic life cycle with a generation in a plant (a myrtaceous host) followed by one in an insect (a Fergusonina fly: Diptera, Fergusoninidae). The nematode and fly have a mutualistic association, with the nematode inducing a plant gall on which the fly feeds and develops, and the fly providing transport for the nematode. The life cycle, specificity, diversity and distribution of the nematode are described, and the nematode phylogeny is discussed. Fergusobia is monophyletic but its origins are unclear. This paper raises questions about Fergusobia, including: what model best accounts for evolution of the known diversity of the nematode/fly mutualism?; how are the nematode/fly life cycles coordinated?; how do the nematodes avoid resistance mechanisms of both flies and plants?; what cecidogenic processes does the nematode use?; and what is the form of parthenogenesis occurring in Fergusobia and how does it relate to the inheritance of variability? Given the models of genomes and transcriptomes now available for other plant-parasitic nematodes and the availability of technologies to examine Fergusobia, it should be possible to answer some of these questions and begin to understand how Fergusobia nematodes might have evolved.