Phytomyza triostevena Eiseman & Lonsdale 2021, spec. nov.
Creators: name: Eiseman, Charles S.
name: Lonsdale, Owen
name: Linden, John Van Der
name: Feldman, Tracy S.
name: Palmer, Michael W.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Agromyzidae
Phytomyza
Phytomyza triostevena

description: Phytomyza triostevena Eiseman & Lonsdale, spec. nov.
(Figs. 53–56, 86, 154–158)
Holotype. USA. IOWA: Allamakee Co., 5.ix.2017, puparium removed from midrib 26.ix.2017, adult em. by spring 2018, J. van der Linden, ex Triosteum, # CSE4663, CNC1144064 (1♁).
Etymology. The specific epithet is a noun in apposition, a portmanteau referring to the position of the larval mines in the veins and midribs of leaves of Triosteum L. (L. vena —a vein).
Host. Caprifoliaceae: Triosteum L.; similar leaf mines have been found on T. aurantiacum E.P.Bicknell (Mews 2019a).
Leaf mine. (Fig. 86) The larva initially forms a narrow, serpentine mine in the leaf blade. It soon enters a lateral vein and follows this to the midrib, in which it feeds until mature.
Puparium. (Fig. 56) Brown; formed within the midrib, near the base of the leaf.
Phenology and voltinism. Leaf mines have been observed beginning in early September, with adults probably not emerging until the following spring.
Distribution. USA: IA; similar leaf mines have been found in Canada: ON (Mews 2019a).
Adult description. Wing length 1.8 mm (♁). Female unknown. Vein dm-m absent. Eye height divided by gena height: 3.5. First flagellomere rounded, as long as high. Orbital plate well-defined, pruinose, narrowing anteriorly. Frontal vitta minutely pitted, appearing darker. Cheek well-developed. Thorax subshining.
Chaetotaxy: Two ori (anterior seta slightly shorter and positioned closer to eye margin); one ors. Ocellar seta subequal to anterior ori; postvertical subequal to ors. Four dorsocentral setae, decreasing in length anteriorly, with anterior two much shorter (less than half length of first seta). Approximately four to five irregular rows of acrostichal setulae.
Coloration: (Figs. 53–55) Setae dark brown. Body dark brown to black; with thick greyish pruinosity on thorax that is more distinct on scutum; gena, parafacial and lunule brown; inner margin of orbital plate beige; halter whitish-yellow. Calypter yellow, hairs light brown.
Genitalia: (Figs. 154–158) Surstylus small, rounded, fused to venter of epandrium, curved posteriorly with dense apical cluster of short setae. Cercus small. Hypandrium broadly rounded; inner lobe V-shaped with two medial setae. Postgonite simple and narrow with one seta. Phallophorus cylindrical with anterodorsal margin lengthened to reach base of basiphallus; lateral lobe simple, narrow. Basiphallus consisting of one pair of long, narrow plates with irregular margins and narrower apices; right plate with base positioned dorsally, left plate with base wrapping around venter. Hypophallus (one pair of lateral sclerites) small, irregular-ovate in outline. Mesophallus not evident. Paraphallus very small, with irregular subovate outline. Distiphallus sharply angled dorsally, thick with apex narrower and slightly curved; seen “ventrally”, outline X-shaped with short arms and long middle section, with apical arms shorter, irregular and less well-defined, each ending in its own small membranous lobe. Ejaculatory apodeme not found.
Comments. This is the second agromyzid to be reared from Triosteum, after Aulagromyza orbitalis. Also in Iowa, we have found mines representing two other Phytomyza species, presumably likewise in the periclymeni superspecies. One is an entirely linear mine in the leaf blade, with frass in closely spaced grains and with a brown puparium formed at the end; the other is digitate and centered on the midrib, similar to those of P. chamaemetabola (Griffiths) and P. gregaria Frick on Lonicera involucrata (Richardson) Banks ex Spreng. (Griffiths 1974).
Phytomyza triostevena is a modestly sized and almost entirely dark species with one ors and pale greyish-blue pruinosity on the thorax. Among the Caprifoliaceae mining Phytomyza, it can be differentiated by having numerous rows of acrostichal setulae, and a small pair of lateral sclerites on the hypophallus that are irregularly ovate in outline and positioned distal to the end of the basiphallus; this combination of characters will key it approximately to P. nigrilineata (Griffiths) in Griffiths (1974). The small, upturned distiphallus must be examined for confident diagnosis; in lateral view, it is relatively stout with the apex narrowed and curved, and in ventral view, is more than twice as long as wide with shallow bifurcations at either end, appearing somewhat X-shaped; the distal points are shallower, somewhat ill-defined and annulated.
description: Published as part of Eiseman, Charles S., Lonsdale, Owen, Linden, John Van Der, Feldman, Tracy S. & Palmer, Michael W., 2021, Thirteen new species of Agromyzidae (Diptera) from the United States, with new host and distribution records for 32 additional species, pp. 1-68 in Zootaxa 4931 (1) on pages 39-40, DOI: 10.11646/zootaxa.4931.1.1, http://zenodo.org/record/4545337