Rhopalomyia guttata Dorchin

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 : 14-15

Rhopalomyia guttata Dorchin n.sp.

Adult: Antenna with 16–18 flagellomeres in male, 18–19 in female; last flagellomere tapered, longer than preceding, or “budding” from it ( Figs. 1–2 ); necks of male flagellomeres III–VII 0.36–0.67 times as long as nodes; female flagellomeres without necks. Palpus 2-segmented; first segment only slightly longer than wide, second segment at least twice as long as first, rounded apically, setulose, with several long setae and elongate, dark scales ( Fig. 3 ). Wing length 1.9–2.3 mm in male, 2.2–2.5 in female, covered by dark, hair-like scales. Legs densely covered by brown scales. Claws untoothed; empodia longer than claws. Male abdomen: tergites 1–7 with posterior row of setae, band of setae mesally, and a pair of anterior trichoid sensilla, weakly sclerotized between mesal and posterior rows of setae; tergite 8 without setae. Sternites weakly sclerotized, with posterior row and mesal group of setae and pair of anterior trichoid sensilla. Male terminalia ( Fig. 12 ): cylindrical, rounded proximally, with setose mediobasal lobe; gonocoxal apodeme undivided, with small, anterior projection; gonostylus short and wide, narrows only slightly toward apex, setose and setulose throughout, with brush-like tooth; aedeagus cylindrical, rounded apically; hypoproct entire or with very shallow apical notch, setose and setulose; cerci separated by deep triangular notch, setose and setulose. Female abdomen (Fig. 28): tergite 8 Y-shaped, proximal arms about third the length of shaft, each with anterior trichoid sensillum; tergite 7 rectangular, weakly sclerotized along margins, with two anterior trichoid sensilla, several rows of setae posteriorly, and groups of setae mesolaterally; sternites with two adjacent trichoid sensilla anteriorly, band of setae on proximal half and row of setae posteriorly, unsclerotized between proximal band and posterior groups of setae; ovipositor 10.7–12.6 times as long as tergite 7.

Pupa: unknown.

Type material: Rhopalomyia guttata Dorchin. Holotype: male, USA, Meriden, CT, Hubbard Pk., 18/IX/ 1998, R.J. Gagné, ex. capitulum gall on S. bicolor , deposited in USNM. Paratypes: 2 males, 3 females, same data as holotype.

Host: Solidago bicolor

Gall and biology: the galls were found by R.J. Gagné in capitula, carried on a pedicel among normal capitula but shorter and hidden by them. The gall is conical-cylindrical, smooth, white to green, or sometimes red, and apically tapering. Each gall contains a single larva. A galled capitulum is wider and harder to the touch than capitula without galls. Galls of R. guttata differ from the capitula galls of R. anthophila and R. racemicola in being smooth rather than bristly. The galls of R. racemicola further differ from those of R. guttata in being onion-shaped rather than cylindrical, and the galls of R. anthophila , although cylindrical, lack the pedicel and the tapering apex that are present in galls of R. guttata .

Etymology: The species is named after its droplet-shaped galls.

Remarks: This is one of the smallest species of Rhopalomyia on goldenrods, but females have the longest ovipositor relative to their body size. It generally resembles the other species that develop in capitula – R. anthophila , R. cruziana , and R. racemicola , whose females are difficult to distinguish from each other, other than the fact that R. cruziana has an exceptionally short ovipositor. Males of R. guttata and R. anthophila have proximally rounded gonocoxites as opposed to the proximally angular gonocoxites of R. racemicola , whereas, R. anthophila is unique for the meso-apical projection of the gonocoxite that is absent in all other capitulagalling species.

The galls of R. guttata were found on silverrod ( S. bicolor ) in Connecticut but not in Pennsylvania or New York. It is possible that the galls escaped our attention on silverrod and possibly on other Solidago species, given their small size and being hidden among normal capitula. Dry galls that appear similar to those of R. guttata have been recorded from S. altissima ( Gagné 1989) but no adult gall midges were reared from them.

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