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

Abstract

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.larva and a number of associated nematodes. This was the first report of a nematode from galls on myrtaceous plants. Later, the nematode was described by G.A. Currie in the new genus Fergusobia and specimens from Eucalyptus stuartiana (now E. bridgesiana) were described as F . tumifaciens (Currie, 1937). Currie found males and parthenogenetic females, but the infective pre-parasitic female was not recognised until John Fisher made an ex-

Family groups of Diopsoidea and Nerioidea (Diptera: Schizophora)—Definition, history and relationships

“…Characters supporting Diopsoidea include: (5) pedicel with dorsal seam (expanded in Gobryidae, lost in Megamerinidae and Diopsidae); (7) first flagellomere elongate (found frequently elsewhere, reversed in Megamerinidae and Diopsidae); (59) vibrissa lost (reversed Somatiidae, independently derived in Nerioidea, Lauxaniidae and Lonchaeidae); (78) proepisternal seta absent (also lost in Anthomyzidae and several lineages of Nerioidea); (87) anterior notopleural seta absent (recovered Gobryidae, also lost several times in Nerioidea); (135) katepisternal seta absent (also lost several times in Nerioidea); (173) alula reduced (highly homoplastic and sometimes subject to interpretation); (174) basal costal setae absent (recovered in Nothybidae, paralleled frequently elsewhere); (203) large body size (reversed in some, paralleled in Nerioidea); (249) male genitalic and pregenitalic sclerites almost symmetrical (due to reduction and possibly not homologous across diopsoid families, as opposed to the more complex state seen in Cypselosomatidae and Pseudopomyzidae; also Agromyzidae).…”

“…The family group can be defined by the following characters (noting that genitalic character states are unknown for Cypselosomatites): (60) ocellars reduced (not Cypselosomatites); (78,90,103) postpronotal, presutural intraalar and anepisternal setae absent; (187) M 4 reaching wing margin; (225) female segment 8 longitudinally striated (also some Diopsoidea); (236) at least three spermathecae (uncommonly reversed); (251) male sternites 7 and 8 deeply divided along adjoining margins (not fused or connected along thickened margin); (263) one or two supernumerary sclerites present; (275) male cercus positioned past epandrium, not sunken within it; (285) hypandrium with membranous anteroventral attachment to pregenital sclerites and epandrium.…”