Rhopalomyia anthophila ( Osten Sacken 1869 )

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 : 6-7

Rhopalomyia anthophila ( Osten Sacken 1869)

Cecidomyia anthophila Osten Sacken 1869: 302 ; Felt 1908: 364 ( Rhopalomyia ).

Adult: Antenna with 16–19 flagellomeres in male, 15–19 in female; necks of male flagellomeres III–VII 0.60–0.86 times as long as nodes; female flagellomeres without necks. Palpus 2-segmented; second segment thinner, 1.5 times as long as first in female, more than twice as long as first in male ( Fig. 4 ). Wing length 2.2–2.8 mm in male, 2.2–2.7 mm in female. Legs densely covered by dark scales. Male abdomen: covered by dark, hair-like scales. Sternites 2–8 with a posterior row of setae, a band of setae mesally, and pair of adjacent trichoid sensilla; weakly sclerotized between two bands of setae. Male terminalia ( Figs. 9–10 ): gonocoxite cylindrical, with apicoventral projection, setose and setulose, with setose mediobasal lobe; gonocoxal apodeme truncate to broad, undivided; gonostylus stout, only slightly narrowed toward apex, setulose throughout, with small brush-like tooth; aedeagus conical, rounded apically; hypoproct M-shaped, setose and setulose; cerci wide, separated by a deep notch, setose and setulose. Female abdomen (Fig. 26): scales and setation as in male; tergite 8 Y-shaped, with two trichoid sensilla anteriorly and a group of setae posteriorly; ovipositor 8.2 times as long as tergite 7.

Pupa ( Figs. 40–41 ): Antennal bases developed into small horns, rounded posteriorly, tapering abruptly toward tip, pointed anteriorly. Posterior margins of antenna bases V-shaped in frontal view. Frons without projections. Cephalic seta long, originating from inflated base.

Type material: Cecidomyia anthophila Osten Sacken. Syntypes: 2 males (pinned), collected by Osten Sacken near Brooklyn, NY, IX/1867, ex. capitulum galls on S. altissima , deposited in the Museum of Comparative Zoology, Cambridge, Massachusetts ( MCZC).

Other material examined: 1 male, 1 female, undisclosed locality and collector, 13/IX/1885, ex. S. altissima ( S. canadensis of Felt), Felt # C1039 deposited in Felt Collection; 1 male, Canada, Ontario, Toronto, W.M. Brodie, deposited in USNM; 11 males, 12 females, USA,, Freese Rd. & Fall Creek, NY, 6/IX/1986, M.V. McEvoy; 8 pupae, USA, Etna, NY, 7/IX/2007, N. Dorchin and M. Wise. Felt (1915) mentioned galls that were collected in three other localities: Asheville, NC on 16/IX/1906; near Albany, NY in September; and Bushburg, MO on 11/IX/1876 by C.V. Riley.

Host: Solidago altissima

Gall and biology: Osten Sacken (1869) included an exemplary account of the galls and their phenology in the original description of this species. The gall ( Figs. 56–57 ) constitutes a modified capitulum. It is cylindrical, 5–10 mm long and 2–3.5 mm wide, usually slightly wider at base than at the tip. The gall is green but densely covered by short, white hairs that give it a whitish, fuzzy appearance. Galls are almost always situated among normal capitula, and are accompanied by tiny leaves and/or ray florets at their base. Each gall contains a single smooth, thick-walled chamber. Inside this chamber is an inner, conical chamber with very thin walls, containing a single larva, facing downwards. Larvae turn to face upwards inside the gall before pupation. The gall’s wall is much thinner apically than laterally, and galls that contain pupae sometimes have slits at their tips ( Fig. 56 ). Galls become apparent in mid August and pupation takes place in late August to mid September. This is a relatively rare species that has a very patchy distribution; in 1987 it was found in only two localities and in 2007 in only one locality in the Ithaca, NY area, despite screening thousands of plants in several field sites in New York and Pennsylvania. Galls are found singly or in aggregations on the same inflorescence. Larvae and pupae of this species are attacked by ectoparasitic wasps. Oviposition and overwintering sites are unknown.

Remarks: This species is generally similar to the other capitulum gallers on goldenrods ( R. cruziana , R. guttata , and R. racemicola ), but is distinct for the apicoventral projection of the gonocoxite ( Fig. 10 ). The pupa has well-developed antennal bases and a much longer cephalic seta than that of other Rhopalomyia species from goldenrods whose pupae we studied, although the pupae of the other capitulum gallers from goldenrods are unknown. The shape and structure of the gall are the best characters by which R. anthophila can be distinguished from similar species.

Males we examined had 16–17 antennal flagellomeres, although in his original description, Osten Sacken (1869) states that the few males he reared had 19 flagellomeres. Other aspects of the male description match the specimens we examined.

Figures

FIGURES 1 – 8. 1 – 3. Rhopalomyia guttata; 1. Male distal flagellomeres. 2. Female distal flagellomeres. 3. Mouthparts. 4. Rhopalomyia anthophila mouthparts. Figs. 5 – 8. Rhopalomyia gina; 5. Acropod. Scale bar = 0.05 mm. 6. Male head with 5 proximal flagellomeres. 7. Female head with 5 proximal flagellomeres. 8. Tip of female ovipositor showing fused cerci and hypoproct. Scale bars (except for Fig. 5) = 0.1 mm.

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 40 – 47. Pupal heads. 40. Rhopalomyia anthophila, ventral. 41. Rhopalomyia anthophila, lateral. 42. Rhopalomyia capitata, ventral. 43. Rhopalomyia capitata, lateral. 44. Rhopalomyia clarkei, ventral. 45. Rhopalomyia clarkei, lateral. 46. Rhopalomyia gina, ventral. 47. Rhopalomyia gina, lateral. Scale bars = 200 μm

FIGURES 56 – 61. Rhopalomyia galls. 56. A group of Rhopalomyia anthophila capitulum galls (arrows) among normal capitula. 57. Rhopalomyia anthophila gall. Figs. 58 – 61. Rhopalomyia hirtipes; 58. Young gall. 59. Mature gall at base of plant. 60. Mature gall carried on a ramet about 50 cm above the ground. 61. Mature gall that has split to allow adult emergence; the emergence bag was opened to show the gall.