Youngomyia podophyllae, FELT, 1907

Dorchin, Netta, Joy, Jeffrey B., Hilke, Lukas K., Wise, Michael J. & Abrahamson, Warren G., 2015, Taxonomy and phylogeny of the Asphondylia species (Diptera: Cecidomyiidae) of North American goldenrods: challenging morphology, complex host associations, and cryptic speciation, Zoological Journal of the Linnean Society 174 (2), pp. 265-304 : 293-298

YOUNGOMYIA PODOPHYLLAE FELT, 1907

Dicrodiplosis podophyllae Felt, 1907: 30 .

Hosts and biology

The six species in this genus are inquilines, or possibly predators, in galls of various cecidomyiids in the Nearctic, Neotropical, and Oriental regions ( Gagné, 1989; Gagné & Jaschhof, 2014). Two species are currently known from North America, Youngomyia quercina Felt, 1911 from Quercus in California and Y. podophyllae , which is particularly associated with Asphondyliini galls on Asteraceae host plants in the north-eastern US. In the present study, the large and very active larvae of Y. podophyllae were regularly found in groups of between three and five in galls of all the surveyed Asphondylia species , but were especially common in A. pseudorosa sp. nov. and A. monacha galls. It is unclear whether they actually prey on the gall inducer’s larva, or kill it indirectly by feeding on gall tissue, because feeding behaviour has not been observed directly. Youngomyia podophyllae larvae were abundant in galls from June to September, and the species probably completes at least two generations during this time. The larvae leave the gall to pupate in the ground, and those of the last (fall) generation most probably overwinter in the soil as third instars.

Adult

General colour brownish orange.

Head ( Fig. 88 ): Eye facets round–hexagonal. Palpus foursegmented, with distinct palpiger; segment 1 slightly longer than wide, segment 2 about 3.5 times as long as segment 1, segments 3–4 about 0.75 times as long as segment 2; all segments with several strong setae and otherwise covered by microtrichia. Face with two or three short setae on each side. Labrum and labella elongate, pointed, and strongly setose. Antenna: 12 flagellomeres in both sexes; first two flagellomeres fused. Male flagellomeres 1–11 trinodal ( Figs 93–95 ): first node setulose, with basal whorl of strong setae and distal whorl of long-looped circumfila, followed by long, bare neck; second node setulose, with one median circumfilar whorl, followed by short setulose neck; third node setulose, with basal whorl of strong setae and whorl of long-looped circumfila, followed by long, bare neck. Flagellomere 12 ( Fig. 95 ) with third node followed by smaller, vestigial setulose appendage bearing few setae, ending in short, apically rounded neck; both proximal and distal flagellomere necks longer in distal flagellomeres than in proximal ones ( Figs 93, 94 ): neck 1 to node 1 ratio 0.67–1.34 for flagellomere 3 (N = 17), 1.13–1.98 for flagellomere 10 (N = 10); neck 2 to nodes 2 + 3 ratio 0.44–0.54 for flagellomere 3 (N = 17), 0.54–0.79 for flagellomere 10 (N = 10). Female flagellomeres cylindrical, setose and setulose, with simple circumfila and short, setulose necks of same relative length throughout antenna ( Fig. 89 ): neck to node ratio for flagellomere 5, 0.24–0.28 (N = 5). Flagellomere 12 with short vestigial appendage, setose and setulose, rounded apically ( Fig. 90 ).

Thorax: Legs: very long and slender. Tarsal claws curved close to base, with long, thin tooth and a tiny, barely visible proximal second tooth ( Fig. 91 ); empodia much shorter than bend in claw. Wing ( Fig. 92 ): transpar- ent, covered by hair-like microtrichia; length 2.47– 3.70 mm in male (N = 19), 2.49–4.22 in female (N = 17). R1 joins C at third of wing length, R5 joins C far beyond wing apex, Rs incomplete, situated slightly beyond midlength of R1; M weak, CuA forked.

Female abdomen ( Fig. 98 ): Sclerites rectangular, weakly sclerotized, with posterior row of setae, several scat- tered setae on mid-proximal part, and pair of proximal trichoid sensilla. Abdomen not protractible. Cerci large and bulbous, bearing evenly scattered setae and densely covered by short, peg-like setulae.

Male abdomen: Tergites 1–7 rectangular, with posteri- or row of setae, a group of setae at mid-proximal part, and pair of proximal trichoid sensilla; tergite 8 completely undifferentiated from surrounding membrane. Sternites 2–7 rectangular, with posterior row of setae, numerous setae on proximal half, and a pair of closely adjacent trichoid sensilla. Sternite 8 smaller and more setose than preceding sternite.

Male terminalia ( Figs 96, 97 ): Gonocoxites slender, widely splayed, with numerous very strong setae on distal half, a prominent angular lobe basoventrally, and conspicuous setose lobe basodorsally. Gonostylus long, slender, evenly arched, with numerous setae on distal twothirds, bearing small apical tooth. Aedeagus wide, almost heart-shaped at apex, extending far beyond hypoproct. Hypoproct conspicuously and densely covered by short, blunt setae, rounded at apex. Cerci thin, deeply separated and splayed, with several strong setae along posterior margin, setulose throughout.

Larva (third instar) ( Fig. 100 )

Bright orange, very long and slender. Length 2.19– 5.14 mm (N = 19). Integument covered by tiny spicules, spiracles conspicuously protruding above body surface. Antennae about 1.5 times as long as wide; cephalic apodeme much longer than head capsule. Spatula ( Figs 99, 100 ) long and robust, with two large triangular teeth and long shaft, on each side with two groups of three tiny lateral papillae; two setose, one asetose in each group. Terminal segment on each side with four setiform papillae on slightly elevated bases.

Pupa ( Fig. 101 )

Small pointed antennal horns; no facial horns. Face on each side with pair of papillae medially, one setose, one asetose, and a group of three asetose papillae laterally. Prothoracic spiracle conspicuously long, pointed and strongly sclerotized; trachea ends at apex. Abdominal segments, except for first and last, each with one proximal row of long and slender barbed spikes, and otherwise covered by tiny spicules.

Notes

Several larvae of this species were found in Felt’s slidemounted collection, in which they were attributed to Asphondylia because they were taken from Asphondylia galls; however, larvae of the two genera can be easily distinguished from each other and the labels on the relevant specimens were therefore amended.

Material examined

1 larva, USA, NY, Albany, 26 August 1907, EP. Felt, ex gall on Solidago patula (USNM) ; 1 larva, USA, NY, Albany, 26 August 1907, E.P. Felt, ex gall on Solidago odora (USNM) ; 1 larva, USA, MA, Magnolia, 26 August 1908, EP. Felt, ex Asphondylia gall on Aster sp. (Felt no. 1891) (USNM); 2 larvae, USA, MD, Wheaton Pk. 15 July 1968, R.J Gagné, ex. gall on Solidago altissima (USNM) ; 2 larvae, USA, MD, Wheaton Pk., 22 August 1970, R.J. Gagné, ex Asphondylia monacha gall on Solidago juncea (USNM) ; 12 larvae, USA, PA, Lewisburg, 8 August 2005, N. Dorchin, ex Asphondylia monacha galls on S. juncea ; 10♂, 4♀, USA, PA, White Deer Creek, 4 July 2007, N. Dorchin and D. Ryan, ex Asphondylia pseudorosa sp. nov. galls on Euthamia graminifolia ; 5♂, 7♀, USA, PA, Mauses Creek, 4 July 2007, N. Dorchin and D. Ryan, ex Asphondylia pseudorosa sp. nov. galls on Euthamia graminifolia ; 3♂, 2♀, USA, PA, Millersburg, 4 July 2007, N. Dorchin and D. Ryan, ex Asphondylia pseudorosa sp. nov. galls on Euthamia graminifolia ; 5 exuviae, 1♂, 5♀, USA, PA, Bucknell University Chillisquaque Creek Natural Area, 15 July 2012, N. Dorchin, ex Asphondylia pseudorosa sp. nov. galls on Euthamia graminifolia .

PHYLOGENETIC ANALYSIS

The complete molecular data set of cytochrome c oxidase subunit I (COI, 53 sequences) and elongation factor 1 alpha (EF-1α, 33 sequences) consisted of 1047 positions (690 COI and 357 EF-1α). All sequences are deposited in GenBank (http://www.ncbi.nlm.nih.gov/) and accession numbers are provided in Table 1. Tree topologies inferred from the mitochondrial COI and from the nuclear EF-1α genes are largely compatible (Figs 102, 103). The combined phylogenetic analysis yielded five well-supported clades representing at least six species of Asphondylia on goldenords ( Fig. 104 ). The previously described species A. monacha and A. solidaginis , and the newly described species A. pseudorosa sp. nov., A. rosulata sp. nov., and A. silva sp. nov., are well supported in this analysis, corroborating inferences drawn from morphological and life-history data. A fifth, early branching clade includes individuals from three different Solidago hosts as well as Asphondylia recondita from Aster novaeangliae . This clade requires further morphological and molecular sampling before systematic conclusions can be reached; the taxa represented by this clade are therefore not described in the present paper.

Analysis of EF-1α (Fig. 102) provides enhanced resolution and support at deeper nodes in the tree, but does not differentiate between A. silva sp. nov. and A. rosulata sp. nov., which form distinct species in the COI tree ( Fig. 103 ), where shallower nodes are

A. clavata 0.9926 A. sp. Gut A. bigeloviabrassicoides A. monacha jun1 A. monacha alt2 0.7178 A. monacha jun2 A. monacha jun3 A. Silva 3 0.9105 A. rosulata gig2 0.3187 A. silva 4 A. rosulata sn2 A. rosulata gig1 1 0.2233 A. rosulata bud4 A. rosulata sn3 0.2726 0.9392 A. rosulata sn1 A. rosulata bud1 A. rosulata bud2 A. rosulata sn4 A. solidaginis bud3 A. solidaginis sn3 0.3981 A. solidaginis sn4 A. solidaginis sn1 0.9325 1 A. solidaginis gig A. solidaginis sn2 A. solidaginis sn5 A. pseudorosa f2 A. pseudorosa b1 0.1705 A. pseudorosa f3 A. pseudorosa f4 A. pseudorosa b2 0.9999 A. pseudorosa f6 A. pseudorosa f5 A. pseudorosa f5 0.5251 A. pseudorosa f1 A. pseudorosa b4 A. pseudorosa b 3 3.0E- 4 Figure 102. Phylogenetic tree of Asphondylia species associated with goldenrods based on Bayesian analysis of partial sequence of the elongation factor 1α (EF-1α) gene. Support values are shown next to nodes. strongly supported. Other discrepancies between the two gene trees include the division in the EF-1α tree to Euthamia -associated and Solidago -associated clades (Fig. 102), whereas in the COI tree the Euthamia clade is nested within the Solidago + Aster clade ( Fig. 103 ). In both trees, A. monacha is most closely related to A. rosulata sp. nov. and A. silva sp. nov., and it is clearly separated from A. solidaginis . Reconstruction of the evolution of host-plant pref- erences among Asphondylia spp. on goldenrods ( Fig. 105 ) reveals a complex history of host-plant use. Maximum- parsimony analyses suggest substantial uncertainty in host-plant usage at deeper nodes in the phylog- eny. Our analyses suggest that S. rugosa is the an- cestral host for the A. rosulata sp. nov. clade with subsequent shifts to S. gigantea , and that A. silva sp. nov. shifted onto and retained S. caesia as its host. The Euthamia -feeding clade shifted onto E. graminifolia early and retained this host, inducing galls in both buds and inflorescences. The history of host use within the A. monacha clade is uncertain, with four different hosts used by the same gall midge species. Our phylogenetic analyses yielded novel insights into contexts of host shifts and the evolution of Asphondylia host–plant relationships in the goldenrod species complex. Further, finer scale patterns of host-plant use (plant-part and gall-type associations) within individ- ual species are revealed with greater granularity ( Fig. 104 ). Asphondylia solidaginis is shown to include individuals from two very different types of galls – a rosette bud gall and a leaf snap – that represent the overlapping spring and summer generations of this species on S. altissima . This species appears to use S. gigantea occasionally as a supplementary host for the leaf snap galls. Asphondylia rosulata sp. nov.

0.002

exhibits a very similar pattern but uses S. rugosa rather than S. altissima as its primary host. Despite the morphological and biological similarity between these two Asphondylia species , they are not closely related. Instead, the sister species to A. rosulata sp. nov. is A. silva sp. nov., which is found exclusively on Soli- dago caesia , on which it completes multiple generations in tiny bud galls throughout the season. The A. monacha clade comprises individuals from complex rosette galls on S. juncea , S. erecta , and S. uliginosa that represent the summer generation of this species. Also included in this clade are individuals from simple bud galls on S. altissima that represent the previously unknown spring generation of A. monacha .

Figures

Figure 103. Phylogenetic tree of Asphondylia species associated with goldenrods based on Bayesian analysis of partial sequence of the cytochrome c oxidase subunit I (COI) mitochondrial gene. Support values are shown next to nodes.

Figure 104. Phylogenetic tree of Asphondylia species associated with goldenrods based on combined Bayesian analysis of the cytochrome c oxidase subunit I (COI) mitochondrial and elongation factor 1α (EF-1α) genes. Support values are shown next to nodes. Colours refer to host-plant species; icons on branches refer to galled plant organ. Rectangular brackets on right indicate species boundaries.

Figure 105. Reconstruction of the evolution of host-plant use by the Asphondylia species associated with goldenrods under maximum parsimony. Branch colours correspond to host species.

Figures 88–95. Youngomyia podophyllae: 88, head; 89, female flagellomere 3; 90, female flagellomere 12; 91, acropod (second tiny tooth on claw not shown); 92, wing; 93, male flagellomere 3; 94, male flagellomere 8; 95, male flagellomere 12. Scale bars: 0.1 mm, except 1 mm for wing.

Figures 96–101. Youngomyia podophyllae: 96, male terminalia, dorsal; 97, male terminalia, inset, ventral; 98, female post-abdomen; 99, proximal part of larval spatula with associated papillae; 100, larval head and prothorax; 101, pupal exuviae, head. Scale bars: 0.1 mm.