Phytomyza lactuca Frost, 1924

Lonsdale, Owen, 2021, Manual of North American Agromyzidae (Diptera, Schizophora), with revision of the fauna of the " Delmarva " states, ZooKeys 1051, pp. 1-481 : 1

Phytomyza lactuca Frost

Figs 802-804

Phytomyza lactuca Frost, 1924: 85. Frost 1928: 77; Spencer 1969: 249; Winkler et al. 2009: 284; Scheffer and Lonsdale 2018: 88.

Chromatomyia lactuca . Griffiths, 1974: 37, 1977: 336; Spencer 1981: 442; Spencer and Steyskal 1986b: 191; Scheffer et al. 2007: 772.

Description.

Wing length 2.2-2.6 mm (♂), 2.1-2.6 mm (♀). Vein dm-m absent. Eye height divided by gena height: 2.3-2.9. First flagellomere large with distal margin rounded; shape variable; larger in female, sometimes circular but usually slightly clavate with anterodorsal region swollen; smaller in male, sometimes with dorsal and ventral margins nearly parallel; hairs very conspicuously elongate, length at least 3 × width of base of arista, becoming longer anterodorsally. Fronto-orbital plate shallowly produced dorsally, smaller than narrow “cheek”.

Chaetotaxy: Two ori with anterior seta either absent or very thin and not more than 1/2 length posterior ori; two ors. Single row of orbital setulae straight to irregular. Ocellar and postocellar setae at least as long as fronto-orbitals. Eye with very sparse short hairs. Two strong rows of acrostichal setulae to midpoint of scutum. Intra-alar setulae relatively few, at least with one well-developed setula in front and behind suture. Four dorsocentrals, decreasing in length anteriorly. Small additional medial presutural supra-alar present.

Colouration: Head light yellow with ocellar tubercle and posterolateral margin of frons dark brown to region between vertical setae or to base or inner vertical; pedicel, first flagellomere, palpus and back of head dark brown; clypeus brown. Thorax dark brown with dense greyish pruinosity that is thicker dorsally and also faintly seen elsewhere on body. Halter white. Calypter margin and hairs brown. Legs dark brown with base of tibiae narrowly yellow and apex of femora yellow for length equal to width of femur at spot. Abdomen brown with posterior margin of tergites 2-6 sometimes yellow.

Genitalia: (Figs 802-804 ) Hypandrium very short and stout; inner lobe with several anterior setae and broad membranous extension that is broadly fused to postgonite. Phallophorus small, shallow; lateral paired sclerites short, dark, slightly pointed apically. Postgonite broad, flat and with several outer setae; apex rounded with dorsal subapical point. Halves of basiphallus crossing at base; left sclerite with ventrobasal process wrapping around shaft, right sclerite with broad laterobasal lobe-like extension. Paraphallus absent. Hypophallus narrow and U-shaped with arms darker and parallel, and distal arch broadly and more weakly sclerotised. Mesophallus not evident. Distiphallus dark, tubular, narrow, and angled ventrally but slightly upcurved, nearly as long as hypophallus. Ejaculatory apodeme small, finger-like; sperm pump small.

Host.

Asteraceae - Crepis , Lactuca , Sonchus , Taraxacum ( Spencer and Steyskal 1986b).

Distribution.

Canada: AB, NL*, ON, PE*, SK*. USA: CA, MD, MI, NC, NY, PA, WV*.

Type material.

Holotype: USA. PA: Arendtville, reared ex. Lactuca scarola var. integrata (1♂, USNM). [Lost]

Material examined.

Canada. NL: Pistolet Bay , 10.viii.1982, G. Cuff, Lot 83-69, 64, CNC480102 (1♂, CNC), ON: Ottawa, 695 Malibu Tr., 45°22'N, 75°43'W, leaf mine Sonchus oleraceus , 3.vii.2015, O. Lonsdale, em. 7.vii.2015, CNC454633-454635 (1♂ 2♀, CNC), Ottawa, 2.vii.2015, O. Lonsdale, leaf mine unknown host, em. 7.vii.2015, CNC454639 (1♂, CNC), Ottawa, 4.ix.1956, G.G. Lewis, serpentine leaf mine in Lactuca canadensis , CNC480104-480106 (1♀, 1♂ 1♀ [same pin], 2 empty puparia [gel capsule], CNC), PE: O’Leary, v.1975, L.S. Thompson, 75-332, CNC480101 (1♀, CNC), SK: Regina, 4.x.1973, M.G. Maw, hand collected, ex Sonchus oleraceus 73-216- Sask, So-R-10, CNC480103 (1♂, CNC) . USA. MD: Bethseda , 28.vi.1980, G.C. Steyskal, ex. Lactuca sp. (3♂ 2♀ [with puparia], USNM), MI: Battle Creek, 25.iv.1936, C.W. Sabrosky (1♂, USNM), WV: Parkersburg, 21.vi.1970, G. Steyskal (1♂, USNM) .

Comments.

The enlarged first flagellomere and very elongate hairs on the first flagellomere are highly diagnostic of this species. As noted in Griffiths (1977), the male genitalia are similar to those in the Phytomyza syngenesiae group, including the pestiferous P. horticola , but the distiphallus of this species is proclinate, and the hypophallus and distiphallus are darker and stouter.

Figures

Figures 802 - 804. Phytomyza lactuca Frost, male genitalia 802 hypandrium and postgonite, ventral 803 hypandrial complex, left lateral 804 phallus, ventral.