Metallactus minax Suffrian 1866
Creators: name: Sassi, Davide
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Chrysomelidae
Metallactus
Metallactus minax

description: Metallactus minax Suffrian, 1866
(Figs 1; 4a–d; 5a–b; 6a)
Metallactus minax Suffrian, 1866: 249; Clavareau, 1913: 93 (catalogue); Blackwelder, 1946: 641 (catalogue). = Metallactus mosei Schöller, 2003: 71 s yn. nov.
Types. Suffrian (1866) did not mention the number of the studied specimens, but he stated that they all came both from Berlin Museum and from Deyrolle’s and Clark’s collections, both of them at present hosted in BMNH. Three putative syntypes, one male and two females, were tracked down in BMNH and five specimens, all females, were available in MNHUB. All these specimens match the original description of the colour pattern and its variation. Suffrian clearly stated that he had only females available for the study. However, as mentioned above, one of the specimens from London is a male. This would suggest excluding at least this specimen from the type series. Nevertheless, certain circumstances led me to a different decision, and this specimen has instead been designated the lectotype of the species. The reasons are as follows. In the species group under study, sexual dimorphism is very reduced. Specifically, the interocular distance is only slightly different when comparing males and females. Additionally, males do not exhibit any easily evident development of the tarsi or anterior tibiae. Furthermore, of notable importance, the fifth anal sternite in males has an unusually deep depression at the apex, curiously similar to that typically observed in females of the majority of Cryptocephalinae. Again, in the original description, Suffrian focuses on the characteristics of the reddish spot in the basal region of the elytra, stating: “ Die Farbe schwarz, ein die schwarz bleibende Schulterbeule umziehender, den Seitenlappen mit einschliessender, nach Innen bis an den dritten Zwischenraum reichender Schulterfleck und die ziemlich breite Spitze, letztere in noch bleicherer Färbung, ziegelroth ”. This description, particularly the detail of the brick-red shoulder spot separated from the apical spot and encircling the black humeral callus, corresponds only to the two specimens from the Clark collection. Besides, only the male exhibits the pronotal coloration that Suffrian describes as "typical", specifically black with lateral margins and part of the anterior margin yellow. No other specimens from London or Berlin display this combination of colours on the pronotum. Furthermore, the male from the Clark collection has the typical handwritten note “a D. Suffrian. determinat.”, which is commonly found on the material studied by Suffrian in the preparation of his monograph (1866). As a matter of fact, there is also a further handwritten note “S Paul” that Suffrian does not mention. However, it should be noted that Suffrian was often not very precise in recording all the collection data, as can be seen in many other instances (see, for example, Sassi 2018, 2022, 2024). Therefore, the most reasonable interpretation of the observed situation is that Suffrian overlooked the presence of a male among the materials he studied. This interpretation is supported by the fact that the German entomologist made the same mistake on other occasions; see, for example, the treatment of the following species and what was stated in the designation of the lectotypes of Metallactus insitivus Suffrian, 1866 and M.taeniatellus Suffrian 1866 (Sassi 2022). For all these reasons, the typification has been made as follows. LECTOTYPE: ♂, glued, aedeagus extracted and glued on the same label bearing the specimen, abdomen glued on a separate label, // “250” [blue label, handwritten] // “S Paul” [one second unreadable word, white label, handwritten] // “E. Coll Chevt.” [white label, printed] // “65.56” [white label, printed] // “a D. Suffrian. determinat.” [white label, printed] // “ Met minax ” [white label, handwritten] // “ Syntype ” [rounded white label with blue margin, printed] // “ Metallactus minax Suffrian, 1866 LECTOTYPUS D. Sassi des.” [red label, printed] // (BMNH). PARALECTOTYPES: 1♀, pinned // ” Metallactus minax Suffr Brazil ” [white label, handwritten) // “Type Suffr Coll. Deyrolle” [white label, handwritten] // “Baly Coll.” [white label, printed] // “ Syntype ” [white label with blue border, printed] // (BMNH); 1♀, pinned // “ Para ” [white label, handwritten) // “ Met. minax ” [white label, handwritten] // "E Coll Laferté" [white label, printed] // "67.56" [white label, printed] // "116" [blue label, printed] // " Syntype " [white with blue border, printed] // (BMNH); 4♀, pinned // “23948” [white label, printed] // “minax Suffr. * c. variet. Brasil C. Sell.” [blue label, handwritten] // (MNHUB); 1♀, pinned // “23949” [white label, printed] // “minax var. Suffr.* Brasil C. Sell.” [blue label, handwritten] // (MNHUB). The label information for these last five specimens matches the registration data from the old catalogue of the MNHUB (“23948 [Metallactus] minax Suffr. * 4. Brasil Sello.” and “23949 [Metallactus minax] var. Suffr.* 1. [Brasil Sello].”). All paralectotypes labelled: “ Metallactus minax Suffrian, 1866 PARALECTOTYPUS D. Sassi det.” [red label, printed].
As regard Metallactus mosei, Schöller (2003) described it based on 44 (47?) specimens. The description was made comparing the external habitus of the specimens with the syntypes of M. minax hosted in MNHUB (which included only females) and highlighting a series of differences primarily in the colour pattern. Unfortunately, the material of the historical collection in MNHUB did not provide a complete picture of the variation range of M. minax, and the lack of male specimens prevented a comparison of the male genitalia. I had the opportunity to study paratypes (of both sexes) of M. mosei and I did not find any significative differences between the two species. For this reason, the following synonymy is here proposed: Metallactus minax Suffrian, 1866 = Metallactus mosei Schöller, 2003 syn. nov.
Type locality. São Paulo (Brazil).
Additional material examined. ARGENTINA: Misiones: Santa Ana I.1952 (1, USNMNH); 12 km SW Santa Ana 21.I.1989 (1, BYU); BRAZIL: Mato Grosso: Maracaju II.1937 (1, USNMNH). Paraná: Jaguariaiva 29.I.1974 (1, AMNH). São Paulo: “ São Paulo ” (15, NMPC & MNHN); Piracicaba II.2002 Lab. Rearing on Eucalyptus urophylla (3, DSPC, LT of Metallactus mosei). PARAGUAY: Amambay: Cerro Cora National Park 19–21.I.2001 (1, NMPC). Asunción: 1891 (7, MNHN). Caaguazú: Caaguazú XII.1943 (1, USNMNH). Central: Capiatá II.1995 (1, MSNM); “Central” 1885 (1, MNHN). Concepción: 120 km NEE Concepción 2–3-II.2008 175 m (5, NMPC & DSPC); Serranía San Luis 23.I.2001 (4, JPPC & MSNG); Concepción (1, HNHMB); “Concepción Corocò” II.1997 (3, DSPC); Orquela Pochon (Horqueta?) I.1936 (1, NHMB). Cordillera: Naranjo II.1995 (3, MSNM); Altos III.1991 (2, DSPC); San Bernardino (3, NMV & MNHUB). Paraguarí: 5 Km W La Colmena 200m 21–22, II.2008 (2, MMPC); Sapucai 1903 (3, BMNH & USNMNH). San Pedro: 5 km N Taquati III.1989 (1, DSPC). “Paraguay” (15, MNHUB & NHMB).
Additional data from literature. BRAZIL: São Paulo: Boa Esperança do Sul (Schöller 2003, locus typicus of M. mosei).
Distribution. Argentina, Brazil, Paraguay. New for Argentina and Paraguay. In my opinion, the indication “Para” on the label of one of the females housed in BMNH would require further confirmation.
Comparative notes. Based on the available material, compared to the other two species in the group, the dorsal black coloration of this species is more extensive, predominantly featuring a pattern with a black pronotum and yellow elytra with a common, large, elliptical black spot in the center. However, this black pattern is often reduced and fragmented, and the pronotum can also be extensively yellow. Due to the elliptical elytral spot and the black coloration of the legs, Metallactus minax could resemble some species of Griburius in the posticatus group (Sassi 2024), such as G. ephippiatus Suffrian, 1866, and G. posticatus Suffrian, 1866. Nevertheless, M. minax can be easily distinguished from them by its more cylindrical profile, which is not dorsally flattened as seen in the typical Griburius habitus of the aforementioned species. Additionally, M. minax is clearly distinct in terms of aedeagal morphology and the shape of the spermatheca, where the ductus, contrary to what is generally observed in Griburius, is long, frail and tightly coiled.
Description of male. Habitus in figs 1a–b (HT). BL = 4.8–5.7 mm, BW = 2.9–3.4 mm, PL = 1.5–2.0 mm, PW = 2.5–3.1 mm. Interocular distance 12.3–14.6 % of BL.
Head: usually completely black, occasionally with small, burred round yellow spot on frontoclypeal suture. Labrum light yellow. Surface of upper frons and vertex quite convex, head punctation sparse but well impressed on vertex, denser on clypeus and along inner rim of eyes, setosity almost missing on vertex and frons, but, again, thick and adpressed along lower part of inner eye margins. Mid-cranial suture apparent between upper half of eyes. Upper lobes of eyes well separated along median line. Ocular lines narrow, strictly adhering to ocular rim, marked by rows of small punctures. Ocular canthus rounded, scarcely setose. Antennae rather long, slender, blackish with first five antennomeres partly yellowish, 3–5 bright, subcylindrical, the subsequent ones dull, moderately flattened and more diffusedly setose.
Pronotum: black, often with longitudinal median yellow stripe extended from anterior to posterior margin, slightly larger posteriorly, spotted with small black marking just in front of scutellum. Lateral margins and external part of anterior and posterior ones yellow as well. Often yellow median stripe can be reduced so not attaining anterior and posterior margins. At times yellow pattern coalesces so black colour reduced to couple of large, oblique, wavy markings at sides of midline. In single specimen from Jaguariaíva (Paraná, Brazil) pronotum totally black (Fig. 1n). Pronotal outline transverse, regularly convex. Lateral margins narrow, regularly curved with maximum width just behind half of length. Posterolateral impression short, shallow. Surface moderately lustrous with scattered, well-impressed punctation, denser on sides, almost obliterated on central part of disc.
Scutellum: completely black, moderately raised. Apex truncated in a straight line or mildly rounded. Surface smooth, minutely and sparsely punctured, with few, short, whitish setae above all on basal half.
Elytra: yellow with common, large, transverse, elliptical black spot at middle of disc. Such black spot can be reduced or broken into separate smaller markings or, as in lectotype, prolonged along suture in broad stripe reaching anterior margin. In single studied specimen (Fig. 1n) from Jaguariaíva (Paraná, Brazil) black pattern extended to cover most of elytral surface leaving yellow colour only on humeral area and apex. Humeral callus always spotted with black even in lighter specimens. Elytral outline cylindrical with sides almost parallel. Lateral margins narrow, scarcely visible from above. Scutellar area not raised. Humeral callus scarcely prominent, not punctured. Elytral punctation fine and weak, rather close, irregularly arranged on anterior half, but hints of more regular rows toward apex. Intervals flat. Epipleura flat or slightly convex, with smooth, impunctate surface.
Pygidium: black, smooth, covered by thick, adpressed, whitish setae and sparse shallow punctures.
Underside: ventral surface black, matt, covered with long, thick, adpressed, yellowish setae, except shiny, scarcely setose, sparsely punctured posterior part of hypomera. Prosternal process narrow, fairly impressed at middle, with apex roughly triangular, slightly raised at tip. Surface of prosternal process covered with long, thick, semi-erect whitish setae. Fifth abdominal ventrite with deep, heart-shaped, bald, impunctate median depression and deeply notched posterior margin.
Legs: black with yellow stripe along anterior margin of anterior femora.
Male genitalia. Median lobe of aedeagus (Fig. 4a–d) subcylindrical with apex blunt, flattened, spoon-shaped in ventral and dorsal view, almost straight in lateral view. Setose depressions shifted to very lateral border of ventral surface, in form of narrow, lengthened callosities, with short, scattered, barely visible setae. Ventral surface just below apex raised in large, squat, pointed median bulge whose distal margin, in lateral view, is fairly concave. At times, such bulge showing two symmetrical indentations (sd in fig. 4d) on apical side so that its base connected to apex by short carina. This pattern is not always evident, and in many cases, surface regularly slanted (Fig. 4a). Endophallus (Fig. 5a) with sclerite I well developed, with large straight-directed denticule. Dorsal spicule well developed, finger-like, with well pigmented apex. Sclerite II slender, slightly convex. Sclerite III robust, sickle shaped. Branches of sclerite IV with surface minutely wrinkled, shorter than sclerite III in folded-up structure, parallel-sided with rounded apex and long sharp process at base.
Female. BL = 6.1–7.1 mm, BW = 3.9–4.3 mm, PL = 2.0– 2.3 mm, PW = 3.3–3.8 mm. Interocular distance 16.9–18.0 % of BL.
Female differs in the larger interocular distance, in the pronotal colouration, which is usually totally black, reduced and finer punctation on the frontoclypeal surface. Additionally, often the ventral yellowish setosity is not as gaudy as in male and does not hide the surface of inferior parts. Besides, the anterior tarsi are slightly narrower.
The fifth abdominal ventrite in females has a large and deep pit. The bottom of the pit is glabrous, matt, impunctate but covered by tiny wrinkles. The vasculum of the spermatheca (Fig. 5b) is moderately pigmented, sickle-shaped with slightly twisted, not swollen proximal lobe. The distal lobe is rather short, slender, tapered with an acute apex slightly bent downwards. The ampulla is not pigmented, short, sitting just at the basal apex of the vasculum. The duct and the sperm gland insertions are perceptibly distinct. The duct is very long, uniform in size, slender, floppy, strictly coiled, with its insertion on the bursa copulatrix forming a rigid, well pigmented sleeve.
Biological notes. Schöller (2003) reported some specimens of the type series of M. mosei to be reared on Psidium guajava (Myrtaceae) and Eucalyptus urophylla (Myrtaceae) (see also Agrain et al. 2024 for the evaluation of the degree in host plant association).
Remarks. Regarding the variability mentioned above, concerning the appearance of the ventral surface of the aedeagal median lobe (Figs 4a and 4d), careful comparisons have revealed that this variability is distributed rather randomly and shows no correlation with either the external coloration or possible partitions of the distribution range. Additionally, different intermediate forms are present, which cannot be attributed to distinct alternative patterns. Based on current knowledge, it does not seem possible to assign taxonomic significance to the variations in this structure within this taxon.
description: Published as part of Sassi, Davide, 2025, Revision of the Metallactus minax Suffrian, 1866 species-group (Coleoptera: Chrysomelidae: Cryptocephalinae), pp. 71-86 in Zootaxa 5583 (1) on pages 73-77, DOI: 10.11646/zootaxa.5583.1.3, http://zenodo.org/record/14798002