Key to the species of Macrostomus in Peru

1 Thorax yellow on mesopleuron, sometimes darker on scutum, scutellum and mediotergite or scutum with black mid-longitudinal stripes........................................................................................... 2

- Thorax mainly black, sometimes with prosternum, postpronotal and postalar lobes partially yellow.................... 8

2 Wing distinctly with brown to black infuscation at level of crossveins r-m and dm-m (Fig. 5A). Female with pinnate setae dorsally and ventrally on mid femur (Fig. 5E) and a few short pinnate setae on basal fourth of mid tibia ventrally and hind femur and tibia with pinnate setae dorsally and ventrally (Fig. 5F) (Bolivia, Peru)...................... M. pictipennis (Bezzi)

- Wing without dark infuscation at level of crossveins r-m and dm-m (Figs 3A, B, 10A). Female with pinnate setae restricted to hind tibia or absent................................................................................... 3

3 Thorax with one mid-longitudinal black dorsal stripe between dorsocentral setae (Fig. 13B).......................... 4

- Thorax without mid-longitudinal black dorsal stripe......................................................... 5

4 Thorax with wide mid-longitudinal stripe, as wide as area between dorsocentral setae (Fig. 13B). Male: hind tibia with tuft of some 15 slender and longer dorsal setae (Fig. 13A). Tergite 8 (Fig. 13D) in dorsal view with elongate projection notched medially. Female: Genital fork wide with U-shaped mid-distal cleft (Fig. 14D). Genital chamber membranous with two small sclerites (Fig. 14D) (Peru)............................................................ M. unilineatus sp. nov.

- Thorax with narrow mid-longitudinal stripe, narrower than area between dorsocentral setae (Fig. 12B). Male: hind tibia with four dorsal setae (Fig. 12A). Tergite 8 (Fig. 12D) with bifid distal projection. Hypandrium (Fig. 12M) with a few posterior setae basally and distinct process medially. Female: Genital fork (Fig. 12Q) with indistinct V-shaped cleft distally. Genital chamber membranous (Fig. 12Q) (Ecuador, Peru) ... M. lineatus Rafael & Cumming

5 Female hind tarsus at least with tarsomere 1 whitish to silvery (Fig. 2). Wing (Fig. 2) distinctly brown infuscated. Male unknown (Bolivia and Peru)............................................................ M. argyrotarsis (Bezzi)

- Hind tarsus entirely brown to black. Wing normally without brown infuscation.................................... 6

6 Two pairs of ocellar setae. Male hind femur not crooked, with slightly short stouter setae not concentrated medially (Fig. 10A). Female: hind tibia with short dorsal pinnate setae; sternite 8 (Fig. 10G) with subapical paired sclerotized protuberance, medially with longitudinal, somewhat membranous line, laterally less sclerotized. Genital fork (Figs 10F, G) Y-shaped (Brazil, Ecuador, Peru)................................................................... M. ciliaticosta Rafael & Cumming

- One pair of ocellar setae. Male hind femur distinctly crooked (sinuose) (Figs 3A, C) or clavate (Figs 8A, B). Female unknown............................................................................................. 7

7 Thorax entirely shiny yellow (Figs 3A, B). Hind femur distinctly crooked (sinuose), with dorsal and ventral setae at curved area denser (Figs 3A, C). Mid femur slightly clavate, mainly in dorsal view, with short posteroventral row of spines at distal third (Peru)............................................................................. M. contortus sp. nov.

- Thorax yellow laterally, shiny brown to black on pronotum, mesonotum and scutellum (Fig. 8A). Hind femur clavate, without dorsal and ventral setae as above (Fig. 8B). Mid and hind femora and tibiae slightly curved (Fig. 8B) (Peru)............................................................................................... M. chelicercus sp. nov.

8 Two pairs of ocellar setae.............................................................................. 9

- One pair of ocellar setae.............................................................................. 10

9 Tergite 8 humped with microspinulose lateral expansion (Figs 6B, C); posterior cercus enlarged distally (Figs 6E, F); cell dm slightly projected posteriorly (Fig. 6A). Hypandrium (Fig. 6J) somewhat same diameter along entire length, with posterior setae. Female sternite 8 narrow and split at basal fourth (Figs 6L, M). Genital chamber well sclerotized (Fig. 6M) (Bolivia, Brazil, Ecuador, Peru)..................................................................... M. limbipennis (Bezzi)

- Tergite 8 (Figs 7A–B) not humped, without microspinulose lateral expansion. Posterior cercus same diameter along entire length (Fig. 7C); cell dm truncate posteriorly; Hypandrium (Fig. 7D) somewhat thin, slightly wider distally, without posterior setae. Female sternite 8 (Figs 7E, F) wide and complete. Genital chamber membranous (Ecuador, Peru)............................................................................................. M. penai Rafael & Cumming

10 Wing (Fig. 11A) entirely hyaline; distal section of vein M 4 3X longer than vein dm-m; cell dm short. Abdomen with blue reflection at certain angles (Fig. 11B). Tergite 8 (Figs 11C, D) with short, rounded distal projection, hat-shaped in lateral view (Fig. 11C). Female unknown (Peru)......................................................... M. hyalopteryx sp. nov.

- Wing brown infuscate on apex, notably on pterostigma (Figs 1C, 4B, I); distal section of vein M 4 2X longer than vein dm-m. Cell dm elongate. Abdomen without blue reflection at certain angles. Tergite 8 (Fig. 4C, know only for M. melanothorax) with thin acute distal projection............................................................................. 11

11 Male: tergite 8 (Fig. 4C) with thin acute distal projection. Female: sternite 8 higher laterally on posterior third, ventrally with two less sclerotized spots at distal quarter (Figs 4J, K); genital fork (Fig. 4L) small, somewhat T-shaped (Brazil, Peru)........................................................................... M. melanothorax Rafael & Cumming

- Male unknown. Female terminalia undescribed (probably as above) (Peru)........................ M. apicalis (Bezzi)