Key to the species of the Ambrysus pulchellus species complex 1. Female subgenital plate (SGP) triangular, posterior margin tapered to a rounded apex (Fig. 6F), lateral margins reflexed dorsally; posterior margin of laterosternite VI almost straight (Fig. 6F). Male accessory genitalic process (AGP) capitate, widest apically (Fig. 6B); pseudoparameres straight mesally, with low and inconspicuous rounded apical lobe (Fig. 6C). Both sexes with scutellum with two reniform to ovate dark brown marks (Fig. 6A)..................... Ambrysus vanduzeii Usinger 1'. Female SGP not triangular, posterior margin broad (Figs. 3F, 4F) or with central concavity (Fig. 1F), lateral margins not reflexed; posterior margin of laterosternite VI almost straight (Figs. 1F, 4F) or strongly convex (Fig. 3F). Male AGP wider in distal half, but tapering apically (Fig. 1B) or widest preapically (Fig. 4B), or widest in basal 2/3 (Fig. 3B); pseudoparameres with medial convexity (Figs. 1C, 3C, 4C), tapering to a pointed (Fig. 1C) or narrowly rounded apical lobe (Fig. 4C), or without apical lobe (Fig. 3C). Both sexes with scutellum almost uniformly light brown (Fig. 1A), or uniformly colored (Fig. 4A), or with dendritic pattern (Fig. 3A)........................................................................... 2 2. Female SGP with deep concavity on posterior margin, posterolateral corners slender and posteriorly produced (Fig. 1F). Male AGP uniformly wider in distal half and tapering apically (Fig. 1B); pseudoparameres tapering to a pointed apical lobe (Fig. 1C). Scutellum usually almost uniformly light brown or a heterogeneous pattern of brown tones (Fig. 1A)...................................................................................................... A. buenoi Usinger 2'. Female SGP without deep concavity on posterior margin, posterolateral corners only slightly produced posteriorly (Figs. 3F, 4F). Male AGP widest in basal 2/3 (Fig. 3B) or widest preapically (Fig. 4B); pseudoparameres tapering to a narrowly rounded apical lobe (Fig. 4C) or without an apical lobe (Fig. 3C). Scutellum almost uniformly dark brown (Fig. 4A) or with dark brown dendritic pattern (Fig. 3A)............................................................................... 3 3. Scutellum almost uniformly dark brown (Fig. 4A). Pronotum surface glabrous, body glossy. Female SGP posterior margin rounded and with inconspicuous posterolateral corners (Fig. 4F); posterior margin of laterosternite VI straight (Fig. 4F). Male AGP widest preapically (Fig. 4B); pseudoparameres tapering to a narrowly rounded apical lobe (Fig. 4C).................................................................................................. A. pulchellus Montandon 3'. Scutellum with dark brown dendritic pattern on medium brown background (Fig. 3A). Pronotum surface finely irregular, body not unusually glossy. Female SGP posterior margin with four conspicuous lobes (Fig. 3F); posterior margin of laterosternite VI convex (Fig. 3F). Male AGP widest in basal 2/3 (Fig. 3B); pseudoparameres without apparent apical lobe, posteromesal corners rounded (Fig. 3C)............................................................ A. californicus Montandon

Published as part of Reynoso-Velasco, Daniel & Sites, Robert W., 2018, Revision of the Ambrysus pulchellus Montandon species complex (Heteroptera: Nepomorpha: Naucoridae), pp. 351-377 in Zootaxa 4442 (3) on page 353, DOI: 10.11646/zootaxa.4442.3.1, http://zenodo.org/record/1303687