1	Frons and notum entirely brown. Surstylus with three anterior tubercle-like setae (Fig. 609)	L.galiivora (Spencer)
–	Frons predominantly yellow (Figs 108–115). Notum with most of notopleuron, postpronotum and scutellum yellow (scutellum mostly or entirely brown in some L.violivora). Surstylus usually only with one or two apical tubercle-like setae (L.quadrivittata with numerous minute setae), but not as above	2
2	Scutum yellow in front of scutellum, either broadly (Fig. 108) or narrowly	3
–	Scutum dark in front of scutellum, with yellow markings restricted to lateral and sometimes posterolateral margins	5
3	Eye sparsely short-haired. Posteromedial setulae on scutum inclinate. Mid tibia with two small posteromedial setae. Third dorsocentral (of four) reduced. Surstylus with dark, elongate, apical process (Fig. 584). Epandrium yellow; posterodistal margin with dark bar on inner face. Apex of phallus bifid with tubules spinulose on inner surface (Figs 586, 587)	L.blechi Spencer
–	Eye bare. Posteromedial setulae on scutum reclinate. Mid tibia without posteromedial setae. Four well-developed dorsocentrals, decreasing in height anteriorly. Surstylus with or without spine-like setae. Epandrium brown; posterodistal margin produced into small dark spine. Apex of phallus cup-like	4
4	Anepisternum with small brown spot. Clypeus brownish. Ocellar tubercle brown. Abdomen brown when viewed dorsally. Wing length 1.6–1.7 mm. Height of eye divided by height of gena 4.3. Length of ultimate section of vein M4 divided by penultimate 2.1–4.0. Surstylus tapering apically and with two apical spines (Fig. 598)	L.eupatoriella Spencer
–	Anepisternum yellow. Clypeus yellow. Ocellar tubercle yellow with brown lines radiating from inner margins of ocelli. Abdomen yellow with ill-defined brownish medial stripe dorsally. Wing length 1.8–2.3 mm. Height of eye divided by height of gena 4.6–4.8. Length of ultimate section of vein M4 divided by penultimate 2.0–2.3. Surstylus with curled distal process and no spines (Figs 612, 613)	L.philadelphivora Spencer
5	Parafacial strongly projecting anterior to eye when viewed laterally. At least three ori on each side of frons. One ors	L.deceptiva (Malloch)
–	Parafacial only barely extending past eye when viewed laterally. Two ori, sometimes with third present on one side. Two or (less commonly) one ors	6
6	Both vertical setae surrounded by yellow. (Fig. 111) Two to four (some L.trifolii) rows of acrostichal setulae. Scutum with light dusting of greyish pruinosity	7
–	Outer vertical setae surrounded by dark brown, inner vertical either enclosed or bordering on brown (Fig. 110); some L.brassicae with only vestiges of pigment around base of vertical setae. Always four rows of acrostichal setulae. Scutum shiny to subshiny	8
7	Femora sometimes brown at base on mid and hind legs, and fore femur sometimes also with extensive dorsal mottling. Spot on anepisternum long and rectangular, ~ 1/2 length of sclerite, but sometimes larger (Fig. 112). Posterior margin of tergites (1)2–6 entirely yellow. Acrostichal setulae usually in four rows (sometimes two or three). Surstylus tapering and somewhat truncated apically, with one strong distal spine (Fig. 637). Distiphallus narrow and weakly sclerotised (Figs 638, 639)	L.trifolii (Burgess)
–	Femora entirely yellow. Spot on anepisternum small to absent. Posteromedial margin of tergites brown. Acrostichal setulae in two or (less commonly) three rows. Surstylus broadly lobate and with one strong apical and one weak subapical spine (Fig. 604). Distiphallus large, globular and minutely tuberculate (Figs 606, 607)	L.fricki Spencer
8	Palpus and face brown. Scutellum usually mostly to entirely brown with medial yellow stripe atrophied. Surstylus without spines (Fig. 645–648). Paraphallus widened apically, recurved to fuse with mesophallus medially (Figs 650, 651)	L.violivora (Spencer)
–	Palpus and face yellow. Scutellum with distinct medial yellow stripe. Surstylus with one or two spines. Paraphallus various, but not as above. Only males can be identified further	9
9	Surstylus with two spines. Distiphallus sometimes pale and cup-like, but usually either entirely split medially or very dark and subcylindrical	10
–	Surstylus with one spine. Distiphallus always pale and cup-like	12
10	Anepisternum yellow on dorsal quarter or less. Paraphallus triangular, conspicuous and held out wing-like laterally. Distiphallus composed of two short, separate tubules (Figs 634, 635)	L.trifoliearum Spencer
–	Anepisternum yellow on dorsal 1/2. Paraphallus pale, narrow. Distiphallus undivided	11
11	Wing length 1.2–1.8 mm. Lateral margin of frons sometimes with narrow brown margin. Distiphallus very dark and cylindrical with slight medial constriction (Figs 593, 594)	L.brassicae (Riley)
–	Wing length 2.1–2.7 mm. Fronto-orbital plate entirely yellow. Distiphallus pale, cup-like (Figs 628–631)	L.temperata Spencer
12	Mesophallus fused to distiphallus, which is narrow with wider apical chamber (Figs 642–644). Paraphallus subrectangular and usually much broader apically	L.helianthi Spencer (in part)
–	Mesophallus separate from broader distiphallus. Paraphallus not wider apically	13
13	Wing length 1.7–2.2 mm. Eye height divided by gena height 3.0–4.4. Distiphallus relatively large and broad (seen ventrally), with base wide and truncated (Figs 601, 602)	L.eupatorii (Kaltenbach)
–	Wing length 1.3–1.8 mm. Eye height divided by gena height 4.4–5.8 (Fig. 109). Distiphallus smaller, base slender and rounded; apical, basal, and ventral surfaces better-sclerotised, forming weak C-shape in profile (Figs 624, 625)	L.sativae Blanchard