Fergusobia, Currie, 1937

Davies, Kerrie A., Ye, Weimin, Giblin-Davis, Robin M., Taylor, Gary S., Scheffer, Sonja & Thomas, W. Kelley, 2010, The nematode genus Fergusobia (Nematoda: Neotylenchidae): molecular phylogeny, descriptions of clades and associated galls, host plants and Fergusonina fly larvae 2633, Zootaxa 2633 (1), pp. 1-66 : 15-18

Genus Fergusobia

Anguillulina (Fergusobia) Currie, 1937

Fergusobia ( Currie, 1937) Christie, 1941

Diagnosis (emended from Siddiqi 1986a): Nematodes that, in a mutualism with Fergusonina flies, induce galls on Myrtaceae ; gall forms specific to particular fly/nematode associations, and host species specific; two overlapping generations, one parasitic in plant galls on Myrtaceae , the other entomoparasitic in the haemolymph of female flies.

Plant parasitic forms:

1. Parthenogenetic female. Occur in plant galls. Develop from juveniles deposited by adult fly during her oviposition; these apparently induce development of a new plant gall via feeding. Semi-obese, usually dorsally curved when heat-killed but straight in some species. Less than 1 mm long (ca 250–700 µm long). Body begins to swell immediately posterior to cephalic region. Cuticle with obscure annules, variously marked with transverse striae, appears to be longitudinally striated when viewed with light microscope. Lateral fields usually obscure when viewed with light microscope, may be absent. With SEM, in most species examined the lateral field comprised diagonal striae ( Figs 69–72 ), but may have three lines (two ridges). Cephalic region may or may not be offset, unstriated; circum-oral area flat, raised or depressed, with 6 or 8 apparent ‘sectors’ ( Figs 73–76 ). Stylet knobbed, 5–20 µm long. Opening of dorsal oesophageal gland 2–3 µm behind stylet knobs. Oesophagus with fusiform, non-muscular, glandular ‘corpus’, with pseudovalves. Position of oesophagointestinal junction unclear. Nerve ring just in front of dorsal oesophageal gland. Dorsal oesophageal gland small in some species, large to enormously developed in most (b’= 1.4–8.8), usually with large nucleus with very large nucleolus, and an extension into the ‘corpus’; may have anterior diverticulum, posterior reflex or additional lobe. Secretory/excretory pore opens behind nerve ring, often opposite the nucleus of the dorsal oesophageal gland. Hemizonid at or in front of pore opening. Reproductive tract with a single gonad, prodelphic, may or may not be reflexed, may extend to nerve ring. Vulva a transverse slit ( Fig. 5 ), at ca 75–90% of body length; may be depressed, flat or may have protuberant lips. Vagina anteriorly directed. No post-vulval sac. Uterus extensile in some species; with a quadricolumella; may contain one, two to three or many eggs, and in some species contains juveniles. Oocytes in single or multiple rows. Rectum non-muscular; anus porelike. Tail conoid, short rounded or longer and more slender. In plant gall, parthenogenetic female deposits eggs that develop into amphimictic generation of nematodes. Juveniles generally resembling female, but smaller.

2. Male. Occurs in plant gall. Semi-obese, usually more or less J-shaped when heat-killed, but may be straight, arcuate or dorsally curved (C-shaped). Usually slightly larger than parthenogenetic female of same species (ca 200–600 µm long). Body begins to swell immediately posterior to cephalic region. Cephalic region, cuticle, lateral lines, stylet, oesophagus, nerve ring and secretory/excretory pore as in parthenogenetic female. Dorsal oesophageal gland opening 1–3 µm behind stylet knobs. Dorsal oesophageal gland small to enormously developed, but usually smaller than in parthenogenetic female (b’=1.8–11.6). Reproductive tract with single testis, variable in length, may extend anteriorly past nerve ring, may be reflexed. Testis, seminal vesicle and vas deferens may or may not be clearly differentiated. Spermatocytes in multiple rows, sperm amoeboid. Bursa membranous, smooth or crenate, usually peloderan but may be leptoderan, varying in length and arising near cephalic region in some species, at mid-body length in others, and just anterior to the cloaca in some. Spicules slender to robust, ca 10–40 µm long, usually angular but may be arcuate, with a large, more or less offset manubrium and rounded tip with terminal or sub-terminal opening. No gubernaculum observed. Tail usually ventrally curved, often with ventral side concave, but may be straight and conoid; tip usually rounded. No genital papillae. Present in plant galls before infective females appear; occasionally found with infective female nematodes inside mature fly larvae, but never in adult female flies.

3. Infective stage, pre-parasitic female. Occurs in plant gall. May be similar in size but usually slightly larger and slimmer than parthenogenetic female, i.e., with a smaller ‘a’ ratio; moves more actively than parthenogenetic females or males; ca 220–650 µm long. Straight, arcuate, dorsally curved or J-shaped when heatkilled. Cephalic region may or may not be off-set; cephalic framework weak; circum-oral area usually flat. Stylet knobs smaller and less robust than in parthenogenetic females and males. Opening to dorsal oesophageal gland 1–3 µm behind stylet knobs. Prominent nuclei present in epidermis and intestinal wall, particularly noticeable in body behind vulva. Oesophagus as in parthenogenetic females and males. Dorsal oesophageal gland small to large (b’=1.7–13.6). Secretory/excretory pore behind nerve ring, often obscure. Reproductive tract with single gonad, prodelphic. Vulva a transverse slit at 60–85% of body length; may be surrounded by a cuticular plate, be depressed, or have small lips. No post-vulval sac, but uterus may bulge towards tail in inseminated females. Tract hypertrophied to varying degrees, usually reflexed in region of oesophagus. Vagina usually perpendicular to body axis, but may be directed anteriorly. Uterus apparently extensile, may reach oesophageal region, holds large numbers of sperm. Tail short to medium with tip bluntly rounded or almost hemispherical, or rarely longer and conoid. Only found within galls for a relatively short time, with third instar fly larvae. Following insemination, penetrate into haemolymph of mature female fly larva or pupa, where cuticle is ecdysed, stylet is lost and intestine degenerates.

4. Entomoparasitic female. Occurs in haemolymph in abdomen of adult female Fergusonina fly. Larger than other stages (ca 300–1400 µm long); non-motile. Straight, or slightly dorsally curved when heat-killed; stout. With TEM, seen to be covered with thickened epidermis with thousands of microvilli, through which food is apparently absorbed directly from fly haemolymph. No stylet; oesophagus, intestine and rectum degenerate. Reproductive tract single, greatly hypertrophied, reflexed to coil along body length. Vulva a transverse slit at 70–90% body length. Vagina anteriorly directed or at right angles to body length. Oocytes in multiple rows around a rachis. Eggs deposited in haemolymph of fly; hatch as J2’s and move to fly oviduct. Some J2’s deposited with fly eggs by fly into fresh host tissue during oviposition by fly; nematodes apparently induce development of a new plant gall via feeding.

each described species.

Type species:

Fergusobia tumifaciens ( Currie 1937) Wachek 1955

Syn: Anguilluina (Fergusobia) tumifaciens Currie 1937 ; Anguillulina (Fergusobia) curriei Johnston 1938 ; Fergusobia curriei ( Johnston 1938) Christie 1941 ; (nec Anguillulina tumefaciens Cobb 1932 ; Anguina tumefaciens (Cobb) Filipjev and Schuurmans Stekhoven 1941 ).

Other species:

Fergusobia curriei Fisher and Nickle 1968 ; F. indica ( Jairajpuri 1962) Siddiqi 1986 ; F. jambophila Siddiqi 1986 ; F. magna Siddiqi 1986 ; F. brevicauda Siddiqi 1994 ; F. philippinensis Siddiqi 1994 ; F. fisheri Davies and Lloyd 1996 ; F. quinquenerviae Davies and Giblin-Davis 2004 ; F. cajuputiae Davies and Giblin- Davis 2004; F. dealbatae Davies and Giblin-Davis 2004 ; F. leucadendrae Davies and Giblin-Davis 2004 ; F. nervosae Davies and Giblin-Davis 2004 ; F. viridiflorae Davies and Giblin-Davis 2004 ; F. pohutukawa Davies 2007 , F. ptychocarpae Davies 2008 , and F. brittenae Davies 2010 . Morphospecies, to be described later, have also been collected from A. floribunda , Corymbia sp. , E. camaldulensis , E. cosmophylla , E. delegatensis , E. diversifolia , E. eugenioides , E. fasciculosa , E. fibrosa , E. gomphocephala , E. leucoxylon , E. macrorrhyncha , E. microcarpa , E. planchoniana , E. porosa , E. viminalis , Eucalyptus sp. , M. armillaris , M. decora , M. linariifolia , M. quinquenervia , and Syzygium luehmannii (K.A. Davies, unpub. data).

Figures

FIGURES 69–72. Scanning electron micrographs of lateral fields of parthenogenetic females of Fergusobia. 69: from E. gomphocephala PG. 70: from E. tereticornis TLG. 71: from E. viminalis ‘leafy’ LBG. 72: from E. gomphocephala PG. Scale bars 69–71 = 5 µm; 72 = 2 µm.

FIGURES 73–76. Scanning electron micrographs of anterior end of parthenogenetic females of Fergusobia. 73: from E. planchoniana ‘leafy’ LBG. 76: from E. delegatensis TLG. 77: from E. tereticornis TLG. 78: from E. gomphocephala PG. Scale bars 2 µm.

FIGURES 1–22. Habitus drawings of parthenogenetic females from Fergusobia clades inferred from sequences of D2/ D3. 1: F. magna from C. tessellaris axial bud ‘stem’ galls. 2: from M. linariifolia SBG. 3: from E. camaldulensis TLG. 4: from E. camaldulensis FBG. 5: from E. microcarpa FBG. 6: from E. delegatensis TLG. 7: from E. fasciculosa style gall. 8: from E. gomphocephala PG. 9: from E. planchoniana ‘leafy’ LBG. 10: from E. tereticornis PG. 11: from S. luehmannii PG. 12: F. ptychocarpae from C. ptychocarpa FBG. 13: from A. floribunda TLG. 14: F. fisheri from E. leucoxylon FLG. 15: from Corymbia sp. PG. 16: from E. camaldulensis axial bud ‘stem’ galls. 17: F. quinquenerviae from M. quinquenervia SBG. 18: from M. nervosa BSG. 19: from M. quinquenervia ‘rosette’ gall. 20: from E. obliqua FBG a. 21: from E. obliqua FBG b. 22: from E. viminalis ‘leafy’ LBG. Scale bars = 50µm.