Phytomyza triangularidis Eiseman & Lonsdale 2018, spec. nov.

Phytomyza triangularidis spec. nov.

(Figs. 55, 57, 212–213, 377–382)

Holotype. IDAHO: Boundary Co., Bonners Ferry, Two Mouth Lakes, 29.ix.2012, em. 30.iv.2013, C.S. Eiseman, ex Senecio triangularis, #CSE394, CNC384816 (1♂[head glued to point]).

Etymology. The specific epithet refers to the host plant, Senecio triangularis Hook.

Host. Asteraceae: Senecio triangularis Hook.

Leaf mine. (Figs. 212–213) Upper surface; long, linear, and whitish, with frass in discrete particles; sometimes quite contorted, forming a secondary blotch.

Puparium. (Fig. 57) Black; formed outside the mine.

Distribution. USA: ID.

Adult description. Wing length 2.9mm (♂). Female unknown. Eye height divided by gena height: 4.1. First flagellomere rounded. Notum pruinose. Vein dm-cu absent.

Chaetotaxy: Two ors (posterior ors thinner, 3/5 length), two ori (anterior ori thinner, 3/5 length). Ocellar seta subequal to anterior ors. Postvertical not visible. Four dorsocentral setae, slightly decreasing in length anteriorly. Acrostichal setulae in approximately four to five scattered rows.

Coloration: (Fig. 55) Setae dark brown. Head mostly yellow; antenna, clypeus, palpus, margin of vertex, posterolateral corner of frons to base of inner vertical seta and back of head dark brown; minute brown spot at base of fronto-orbitals; dark brown ocellar spot slightly larger than tubercle; face irregularly brown to light brown; venter of gena with brown line. Body with light pruinosity that is denser on thorax, where it is partly bluish and somewhat coppery. Thorax dark brown, postpronotum and notopleuron mostly light yellow to whitish, region around posterior spiracle whitish, and anepimeron with whitish medial mottling. Calypter white, hairs brown. Haltere white. Legs dark brown with apices of femora narrowly light yellow, only spot on fore femur as long as wide, base of fore tibia yellowish, and tibiae and tarsi paler brown.

Genitalia: (Figs. 377–382) Surstylus small, rounded, fused to epandrium. Hypandrium with shallow apical apodeme and long basal arms. Postgonite with broadly lobate inner process and apex, with one medial seta and one apical socket. Phallus relatively large with phallophorus small and flanked by one pair of irregular, mottled lateral lobes strengthened by darker medial bar. Basiphallus composed of two very narrow, dark sclerites fused to hypophallus; right sclerite wider and paler at base, with irregular margin distally; left sclerite with dense cluster of small spines past midpoint, base curved around shaft ventrally. Hypophallus large, dark, narrow, U-shaped. Paraphallus a thickened membranous band stretching from base of hypophallus to mesophallus, where a long, irregular sclerotized patch is fused to a thickened ventromedial patch on mesophallus. Mesophallus fused to distiphallus, length apparently twice width, mostly clear with ventromedial and distal regions sclerotized. Distiphallus divided into one pair of relatively wide, dark, parallel tubules several times longer than wide with apex slightly flared and haired. Ejaculatory apodeme small, with short stem and reduced, pale blade; sperm pump clear.

Comments. The mines of Phytomyza triangularidis may not be distinguishable from those of P. alpina Groschke (on other Senecio spp. in Europe and western North America), to which it is clearly most closely related and to which it will key in Griffiths (1974b), but the latter is not known to occur south of extreme northern British Columbia (Griffiths 1972b, 1974b). The adult of the new species differs subtly from P. alpina in having the eye margin yellow along the orbital plate, the notopleuron is mostly whitish-yellow (not dark with limited pale mottling around postpronotum and along margin of notopleuron), the mesophallus is directed apically (not angled dorsally), the straighter hypophallus has a much weaker attachment to the basiphallus, and the paraphallus is longer, paler, more irregularly sclerotized and more closely adjoining the spinulose patch of the basiphallus (Figs. 381, 382).