Metallactus kollari (Perty, 1832)

Sassi, Davide, 2018, Revision of the Metallactus kollari species-group with a new diagnosis of the genus (Coleoptera: Chrysomelidae: Cryptocephalinae), Zootaxa 4413 (1), pp. 57-110 : 64-65

Metallactus kollari species-group

The species-group is characterized by the following shared traits. Metallactus of medium to large size, with some kind of “ Clytra ”-like look. Verified BL range is 4.3–6.4 mm in males and 5.2–7.8 mm in females. Dorsal surface yellow with a transverse, sometimes interrupted pronotal black pattern and elytral black spots or stripes typically arranged in three transverse groups, the first one near the anterior margin, the second near the middle and the third, generally smaller, on apex. However, dorsal black pattern widely varying even within species, being sometimes largely coalescent, sometimes almost obliterated.

Antennae rather similar in shape and length among species ( Fig. 13n ) with few exceptions in which antennomeres in males are characteristically elongated ( Figs 12n , 15n ). Posterolateral impressions on pronotum are generally detectable, having importance to some degree in the diagnosis of some species.

The median lobe of aedeagus, contrary to what is observed in different groups of Cryptocephalinae in general, and also in some monophyla of Neotropical Pachybrachina (Sassi, in preparation), in all the species of the present group, with the exception of M. longicornis , does not show any glaring diagnostic characters, having as a whole a rather simplified structure. In fact, the shape is basically cylindrical, with a short, triangular apex; the surface looks smooth, sublucid, devoid of particular ornamentation or structures, except for two slightly depressed scarcely delimited, sometimes barely visible hairy dents bearing sparse whitish erected setae. Hairy dents are constantly weakly defined, shallow, roughly elliptical or subtriangular. Ostium is delimited by two triangular to subrectangular frenula ( Leonardi & Sassi, 2001) separated by a membranous area. In lateral view the ventral profile appears more or less convex, without ever looking really swollen. The apex is constantly weakly bent ventrally. The colour of median aedeagal lobe is generally brownish, but in many cases light yellow. The aedeagal characters described above show a certain degree of variability, and it is not always possible to identify specific diagnostic differences. Therefore, in many cases the mere examination of the median lobe of aedeagus does not result in a secure specific determination.

Legs are devoid of any particular diagnostic characters, basically similar in all of the studied species with the exception of colour pattern, which sometimes provides useful information (see description of the respective species, and identification key). Apex of median and posterior tibia sometimes bearing a tiny spur.

Females are basically very similar to males, with the exception of the biometrical measures, and abdomen markedly more swollen. Dorsal chromatic pattern is variable in the same way and neither the shape of the fore legs nor the length of the antennomeres show remarkable sexual dimorphism. The few exceptions are pointed out in the descriptions of the respective species. Spermatheca is normally sickle-shaped. Spermathecal duct is long, slender, poorly sclerotized, coiled with coils more or less thick. Length of duct and thickness of coils have some diagnostic interest at species level. Rectal apparatus with dorsal sclerites arranged in a transverse line, generally tapered towards the midline. Transverse connection of dorsal sclerites across dorsal fold thin, sinuate in middle. Ventral sclerite large, generally ribbon-like, tapered on sides, less pigmented in middle, with rounded, crenulate apodemes wider than rectum. Lateral fold barely pigmented, devoid of sclerotizations.

Setosity of ventral part has some significance in delimiting sub-groups of species, being far more developed in M. kollari and M. longicornis .

Compared to most other species of Metallactus , the large size, the similarity in the colour pattern and the simplified, tubular shape of the aedeagus allow to delimit quite easily the present species-group. However, given the strong intraspecific variability of the dorsal colour design, it turns out to be difficult to distinguish the species from each other on the basis of the external habitus alone. Of some significance is the colour of the lower parts and legs that, when totally or almost totally black, tends to be constant within a species, thus giving some help in the identification.

Basically, Metallactus kollari species-group matches Suffrian's groups 10 + 11 of his monograph (1866), where 4 and 8 species had been included in groups 10 and 11, respectively. Quoting Suffrian (1866), the species in the two groups are, as reported above, “somehow isolated” and share the following features: “quite large and stout, basically cylindrical in shape; dorsal colour pattern light yellow with a rather variable black pattern”. Besides, Suffrian pointed out that species in the group 10 are different from those in group 11 for a slightly slimmer and more conical pronotum. Moreover, in group 10 the black pattern is generally in the form of roughly rounded points, while in group 11 it tends to form transverse bands. In addition to these remarks, it is observed here that in Suffrian's group 10 the pronotal black pattern tends to be more angular and obliterated in the middle. When the black pronotal pattern is reduced to two spots, these are often more longitudinally arranged. On the contrary, in group 11 the black pronotal pattern is more transverse, less angular and, if reduced to two separated spots, these turn out to be more transversally arranged. However, all the differences listed above, which in some cases can help in the discrimination of some species, are in fact rather uncertain in the delimitation of two distinct groups. Therefore, even though this distinction has been used in the specific diagnoses for practical purpose, it has not been considered neither sufficiently corroborated nor particularly useful to keep these two groups separated from each other in a formal taxonomic frame.

Describing M. bifasciatus Jacoby (1878) suggested a close relationship with the species discussed in the present contribution, however, M. bifasciatus is clearly different and rather close to the M. fricator species-group (unpublished data). Additionally, it should be reported that Jacoby (1907) described a species from Brazil which he reckoned to belong to the genus Griburius , namely G. nigritarsis , but which actually ought to be placed in the M. kollari species-group. Only a single type of this species is housed in BMNH. Having been able to examine that specimen and to compare it with the syntypes of M. dodecastictus , I am utterly convinced that G. nigritarsis is actually conspecific to M. dodecastictus .

M. kollari species-group has an ascertained distribution spanning from central and southern Brazil to northern and central Argentina, including Uruguay and Paraguay ( Figs 20–36 ).

Finally, little is known about the biology of the species of M. kollari species-group. However, some biological remarks were supplied for some taxa ( M. patagonicus , M. albipes ) in connection with their suitability for biocontrol of Baccharis halimifolia L. in Australia, an invasive alien shrub in cattle pastures ( White 1975; Riding 1983; McFayden 1987).

Figures

FIGURES 13–14. M. rileyi (13), M. bellatrix (14). 13a–b: habitus; 13c–e: median lobe of aedeagus in ventral (c), dorsal (d) and lateral (e) view [1.0 mm]; 13f: sclerites II–III–IV of endophallus [0.6 mm]; 13g: sclerite I and dorsal spicule of endophallus [0.9 mm]; 13h: spermatheca [0.8 mm]; 13k–m: rectal apparatus in dorsal (k) and ventral (m) view [0.9 mm]; 13n: antenna [1.5 mm]. 14a–b: habitus; 14h: spermatheca [0.7 mm]; 14k–m: rectal apparatus in dorsal (k) and ventral (m) view [0.9 mm]. 13a–b: holotype; 14a–b: holotype. Square brackets: length of scale segment.

FIGURES 11–12. M. dodecastictus (11), M. pollens (12). 11a–b: habitus; 11h: spermatheca [1.1 mm]; 11k–m: rectal apparatus in dorsal (k) and ventral (m) view [1.1 mm]. 12a–b: habitus; 12c–e: median lobe of aedeagus in ventral (c), dorsal (d) and lateral (e) view [1.1 mm]; 12f: sclerites II–III–IV of endophallus [0.7 mm]; 12g: sclerite I and dorsal spicule of endophallus [0.9 mm]; 12h: spermatheca [1.1 mm]; 12k–m: rectal apparatus in dorsal (k) and ventral (m) view [1.3 mm]; 11n: antenna [2.2 mm]. 11a–b: lectotype; 12a–b: lectotype. Square brackets: length of scale segment.

FIGURES 15–16. M. longicornis (15), M. londonpridei (16). 15a–b/a1: habitus; 15c–e: median lobe of aedeagus in ventral (c), dorsal (d) and lateral (e) view [1.2 mm]; 15f: sclerites II–III–IV of endophallus [0.6 mm]; 15g: sclerite I and dorsal spicule of endophallus [0.6 mm]; 15h: spermatheca [0.9 mm]; 15k–m: rectal apparatus in dorsal (k) and ventral (m) view [1.4 mm]; 15n: antenna [2.2 mm]. 16a–b: habitus; 16c–e: median lobe of aedeagus in ventral (c), dorsal (d) and lateral (e) view [0.9 mm]; 16f: sclerites II–III–IV of endophallus [0.6 mm]; 16g: sclerite I and dorsal spicule of endophallus [0.8 mm]; 16h: spermatheca [0.9 mm]; 16k–m: rectal apparatus in dorsal (k) and ventral (m) view [1.3 mm]. 15a–b: holotype; 15a1: paratype from Cuyaba, Mato Grosso, Brazil); 16a–b: holotype. Square brackets: length of scale segment.

FIGURES 20–28. Distribution maps for Metallactus kollari species-group. M. affinis (20); M. albifrons (21); M. albipes (22); M. bellatrix (23); M. bezoar (24); M. corruptus (25); M. dodecastictus (26); M. guarani (27); M. kollari (28). Grey squares: localities reported in a generic way.

FIGURES 29–36. Distribution maps for Metallactus kollari species-group. M. languidus (29); M. londonpridei (30); M. longicornis (31); M. patagonicus (32); M. pollens (33); M. regalini (34); M. rileyi (35); M. spilotus (36). Grey squares: localities reported in a generic way.