Rhopalomyia lobata Felt 1908

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 : 19-20

Rhopalomyia lobata Felt 1908

Rhopalomyia lobata Felt 1908: 366 .

Rhopalomyia lanceolata Felt 1908: 367 . New synonym.

Adult: Antenna with 16–17 flagellomeres in both sexes; necks of male flagellomeres III–VII 0.47–0.67 times as long as nodes, necks of female flagellomeres absent to 0.1 times as long as nodes. Palpus 1-segmented, usually no more than 1.6 times as long as wide, shorter in female than in male, rounded or sometimes slightly tapered at tip, setose and setulose. Wing length 2.9–3.2 mm in male, 2.7–3.2 mm in female. Legs densely covered by dark brown scales; Empodia considerably longer than claws. Male terminalia ( Fig. 21 ): gonocoxite relatively slender and angular at base, setose, with strongly setose mediobasal lobe; gonocoxal apodeme wide, proximally divided into two short arms; gonostylus cylindrical, curved in both posterior and anterior margins, setose and setulose throughout, with brush-like tooth; aedeagus wide, rectangular, truncated and often notched apically; hypoproct wide, with very shallow notch, strongly setose and setulose; cerci completely or almost completely fused, forming a single, almost rectangular lamella, sometimes separated by very shallow notch to form a heart-shaped lamella, strongly setulose with many long setae. Female abdomen (Fig. 35) as in R. fusiformae and R. pedicellata ; ovipositor 5.3–6.0 times as long as tergite 7.

Pupa ( Figs. 50–51 ): Orange. Bases of horns undeveloped, with only tiny apical, blunt bump. Posterior margins of antennal bases V-shaped in frontal view. Frons without median projections or ridges, with pronounced lateral projections, posterior edge rounded.

Type material: Rhopalomyia lobata Felt. Holotype: female, USA, W. Nyack, NY, 17/VII/1907, E.P. Felt, ex. E. graminifolia, Felt # a1647, deposited in Felt Collection.

Rhopalomyia lanceolata Felt. Syntypes: 1 male, 1 female, USA, Lake Forest, IL, unspecified date, J.G. Needham, ex. E. graminifolia, Felt # c784, deposited in Felt Collection.

Other material examined (all from E. graminifolia ): R. lobata : 1 female, USA, Big Moon Lake, NY, 29/VII/1985, R.J. Gagné; 9 males, 13 females, USA, Eldridge Wilderness, NY, 7/VII/1987, M.V. McEvoy; 2 pupae, USA, PA, Bucknell University Chillisquaque Creek Natural Area, 23/VI/2005, T. Dowling; 3 males, 3 females, 2 larvae, USA, PA, Bucknell University Chillisquaque Creek Natural Area, 27/VI/2005, N. Dorchin; 3 males, 3 females, USA, Lewisburg, PA, 28/VI/2005, N. Dorchin.

Host: Euthamia graminifolia

Gall and biology: The multi-chambered galls are induced in apical and lateral buds. They are first apparent in mid May, when they form about 1 cm-wide globular swellings in shoot tips ( Fig. 78 ). Some galls occur in clusters around the shoot tip or in adjacent lateral buds ( Fig. 79 ) At this point, several leaves surround a small spongy mass at the base of the gall, which grows gradually over the next month up to a final size of 6 cm in diameter. The small size of the gall given by Felt (1915) probably refers to a gall in a lateral bud or to one of clustered galls in a shoot tip. The leaves that are tightly wrapped around the spongy mass are much wider than the normal, thin leaves of the plant ( Fig. 80 ). Around the second week of June, these leaves begin to loosen, revealing the whitish tissue in which 5–35 larval chambers are embedded. Adults emerge from late June to mid July, at which point the fleshy core of the gall is exposed and empty pupal skins can be seen stuck in it ( Fig. 81 ). Soon after the gall midges emerged, the fleshy tissue turns black, and dry galls remain on the plants for several weeks. No second generation galls were observed, thus this species appears to be univoltine, with first instar larvae probably overwintering in or near the plants.

Remarks: Despite the striking differences in gall structure and morphology, adults of this species are almost identical to those of R. fusiformae and R. pedicellata – the other Rhopalomyia species from Euthamia . Females of all three species share the widely splayed arms of the Y-shaped 8th abdominal tergite, which are longer relative to the shaft in R. lobata than in any other Rhopalomyia species from goldenrods. Males of all three species share the angular and relatively slender gonocoxite, with strongly sclerotized two-armed gonocoxal apodeme, but males of R. lobata often have notched aedeagus and completely fused cerci, compared to the truncated aedeagus and clear notch between the cerci in R. fusiformae and R. pedicellata . The pupa of R. lobata has blunt antennal bases ( Fig. 51 ), as opposed to the small, tapered projections on the antennal bases of R. pedicellata ( Fig. 53 ). The pupa of R. fusiformae is unknown.

Felt (1908) described R. lobata and R. lanceolata in the same work from similar, spongy galls in apical buds of E. graminifolia . The two species are synonymized here based on their morphological similarity, the description of their galls ( Felt 1915), and the fact that we never found any other type of spongy bud galls on Euthamia . It is noteworthy that the cerci in the single male syntype of R. lanceolata are atypically separated by a clear notch, thus resembling those of R. fusiformae and R. pedicellata . It is possible that this specimen represents a less common situation in R. lobata , in which the cerci are partially separated.

Figures

FIGURES 20 – 25. Male terminalia (in dorsal view unless otherwise noted). 20. Rhopalomyia inquisitor. 21. Rhopalomyia lobata. 22. Rhopalomyia racemicola. 23. Rhopalomyia solidaginis. 24. Rhopalomyia solidaginis, ventral. 25. Rhopalomyia thompsoni. Scale bars = 0.1 mm

FIGURES 48 – 55. Pupal heads. 48. Rhopalomyia hirtipes, ventral. 49. Rhopalomyia hirtipes, lateral. 50. Rhopalomyia lobata, ventral. 51. Rhopalomyia lobata, lateral. 52. Rhopalomyia pedicellata, ventral. 53. Rhopalomyia pedicellata, lateral. 54. Rhopalomyia solidaginis, ventral. 55. Rhopalomyia solidaginis, lateral. Scale bars = 300 μm

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.