Rhopalomyia fusiformae Felt 1907

Dorchin, Netta, Mcevoy, Miles V., Dowling, Todd A., Abrahamson, Warren G. & Moore, Joseph G., 2009, Revision of the goldenrod-galling Rhopalomyia species (Diptera: Cecidomyiidae) in North America, Zootaxa 2152, pp. 1-35 : 12

Rhopalomyia fusiformae Felt 1907

Rhopalomyia fusiformae Felt 1907a: 24

Rhopalomyia fusiformis Felt 1907b: 120 , unjustified emendation of fusiformae

Adult: Antenna with 17–18 flagellomeres in male, 16–17 in female; necks of male flagellomeres III–VII 0.47–0.75 times as long as nodes, necks of female flagellomeres 0.08–0.23 times as long as nodes. Palpus 1-segmented, at least 1.5 times as long as wide, slightly tapered, setose and setulose. Wing length 2.6–3.2 mm in male, 2.3–2.9 mm in female. Legs densely covered by brownish scales. Male terminalia ( Fig. 16 ): gonocoxite slender and angular at base, almost same width throughout length, setose, with strongly setose mediobasal lobe; gonocoxal apodeme wide, proximally divided into two short, strongly sclerotized arms; gonostylus curved in both posterior and anterior margins, setose and setulose throughout, with relatively large, brush-like tooth; aedeagus wide, rectangular, truncate, slightly widened distally; hypoproct with shallow notch, strongly setulose; cerci rounded, separated by a small notch, strongly setose and setulose. Female abdomen (Fig. 32): covered by dark, hair-like setae; tergite 7 rectangular, less sclerotized along mesolateral and anterior margins, with two anterior trichoid sensilla, a row of setae posteriorly, and several setae on posterior half; tergite 8 Y-shaped, proximal arms widely splayed, each with anterior trichoid sensillum; ovipositor 5.0–5.6 times as long as tergite 7. Adults are morphologically indistinguishable from those of R. pedicellata , but a recent molecular analysis suggests these are distinct species (Dorchin et al., in prep.).

Pupa: unknown.

Type material: Rhopalomyia fusiformae Felt. Holotype: male, USA, Albany, NY, 16/VII/1906, E.P. Felt, ex. E. graminifolia Felt # a1150, deposited in Felt Collection.

Other material examined (all from E. graminifolia ): 1 female, USA, Albany, NY, 16/VII/1906, E.P. Felt, Felt # a1150, deposited in Felt Collection; 1 male, USA, Albany, NY, 19/VII/1906, E.P. Felt, Felt # a1150, deposited in Felt Collection; 2 males, 1 female, USA, Albany, NY, 20–22/VII/1907, E.P. Felt, Felt # a1150, deposited in Felt Collection; 1 male, 1 female, USA, Hector Backbone, NY, 7/IX/1987, M.V. McEvoy.

Host: Euthamia graminifolia , E. tenuifolia

Gall: the galls of this species ( Figs. 82–83 ) are identical to those of R. pedicellata ( Figs. 84–85 ) except for the lack of a pedicel. This difference is consistent and no intermediate forms were found. The galls are found on leaves, stems and inflorescences, are 6–12 mm long, 1–2 mm wide at the base, and tapered towards apex. Galls are often found in aggregations ( Fig. 82 ). They are smooth, green to purplish-green with longitudinal darker lines, contain a single chamber, and are smooth and shiny on the inside. Each gall contains a single larva and reaches its final size when the larva is still a first instar. Old galls remain on the plant and become brown and hardened. Although galls were abundant in western NY in the Ithaca area, they were completely absent from other localities, and were never found in central PA during a three-year study that involved many field sites. In western NY, this species completes at least two generations per year, with adults emerging in early to mid July and again in late August and early September. Galls were also found on E. tenuifolia in NJ but no adults were reared from them and they are attributed here to R. fusiformae based on their galls alone. This species is heavily attacked both by ectoparasitoids and by polyembryonic endoparasitoids. In a sample that included hundreds of galls in September 2007, parasitism rates reached virtually 100%, as only a single gall was found to contain a viable gall inducer.

Remarks: Adults of R. fusiformae are morphologically indistinguishable from those of R. pedicellata and their galls differ only in lacking the long pedicel that is present in galls of R. pedicellata . However, galls of intermediate morphology were never found and a recent molecular analysis (Dorchin et al., in prep.) suggests that the two species are distinct. Males of all three species from Euthamia have elongate and slender gonopods and a two-armed gonocoxal apodeme, whereas females have a strongly posteriorly setose tergite 7 and widely splayed arms of the Y-shaped tergite 8. Species from Solidago hosts with morphologically similar males are R. clarkei , R. inquisitor and R. gina , which all have one-segmented palpi, two-armed gonocoxal apodemes, and all develop in single-chambered, inconspicuous leaf and stem galls.

Figures

FIGURES 9 – 19. Male terminalia (in dorsal view unless otherwise noted). 9. Rhopalomyia anthophila. 10. Rhopalomyia anthophila, left gonopod, ventral. 11. Rhopalomyia bulbula. 12. Rhopalomyia guttata. 13. Rhopalomyia capitata. 14. Rhopalomyia clarkei. 15. Rhopalomyia cruziana. 16. Rhopalomyia fusiformae. 17. Rhopalomyia hirtipes. 18. Rhopalomyia gina. 19. Rhopalomyia gina, lateral. Scale bars = 0.1 mm

FIGURES 78 – 85. Rhopalomyia galls. Figs. 78 – 81. Rhopalomyia lobata. 78. Young gall in apical meristem. 79. Young galls in lateral meristems (arrows). 80. Mature gall showing modified, broad leaves sheathing the fleshy gall center. 81. Mature gall showing exposed, fleshy center after onset of adult emergence. Figs. 82 – 83. Rhopalomyia fusiformae; 82. Aggregation of galls on stem and leaves (arrows). 28. Gall, showing longitudinal ridges and lack of pedicel. Figs. 84 – 85. Rhopalomyia pedicellata. 84. Group of galls situated on long pedicels among capitula. 85. Gall arising from stem, carried on long pedicel.