Anthrax trimaculatus Macquart 1848

Anthrax trimaculatus Macquart

Anthrax trimaculatus Macquart, 1848, p. 194 [trimaculata].—Kertész 1909, p. 56.—Marston, 1964, p. 104.

Argyramoeba imitans Schiner, 1868, p. 122.—Van der Wulp, 1882, p. 86.—Kertész, 1909, p. 64.

Anthrax imitans.—Painter, 1933, p. 5 [initans].

MALE.—Body generally black, tibiae, margins of apical abdominal segments, and sometimes femora and margins of proximal abdominal segments red orange. First antennal segment inverted conical, about 1.5 times apical width; second segment buttonlike, about one-half wider than long; bulbous basal part of third segment slightly narrower than second segment, attenuating to styliform part, which is about as long as base and twice as long as style. Front with black setae and scattered, linear, yellow scales; face with black and white setae along oral and lateral margins, bare on upper half below antennae. Occiput with black setae and linear gold scales on upper third, with white setae and scales below; fringe of pile on posterior margin black or yellow on upper third, white below and behind vertex.

Disc of mesonotum with fine black setae and linear scales, white in posteriorly bifurcate medial stripe and transversely in front of bases of wings, light yellow to gold elsewhere, submedial spots of black scales present posteriorly on specimens with gold scales; lateral and posterior margins with long, linear, semirecumbent white or white and yellow scales and black setae and macrochaetae. Scutellum with black setae and linear scales varying from yellow on disc and white on margins to black on disc and gold on margins. Sternopleuron, mesopleuron, and anterior part of pteropleuron with fine white setae and linear white scales, some black and gold macrochaetae present dorsally on last two. Propleuron, prostemum, and anterior margin of mesonotum with white or yellowish-white pile, some black setae on latter. Postalar tuft of pile white or yellowish white. Metapleuron bare or with few linear white scales just above coxa. Coxae with black, gold and white bristles and linear and lanceolate white scales.

Wing (Plate 6c) hyaline with light or dark brown spots at bases of cells R2+3, R5, 1M2, Cu1, postmedially in cell R1, and below base of cell R1 in cell R; spots varying from small and distinct to large and confluent; base of cell 2M2 with very small spot in darker specimens. Bases of cells R2+3 and R4 with basal spurs about as long as basal sections of veins. R–m crossvein at basal two-fifths of cell 1M2, vein R2+3 arising opposite; contact of cells 1M2 and Cu1 about 1.5 times longer than width of base of cell Cu1. Cell 2A 1.0 to 1.5 times as wide as cell 1A; alula well developed with posterior margin distinctly convex. Calypter unpigmented, fringe of hair white. Stem of halter light to dark brown, knob dark brown basally, yellow apically.

Anterior sides of femora with black and dark brown scales apically and yellow to gold scales basally, posterior sides with white scales. Fore and middle tibiae with black scales anteroventrally and white scales elsewhere; hind tibiae with mixed black, white, and yellow scales. Middle femur with anteroventral row of macrochaetae; hind femur with anteroventral and posteroventral rows.

First abdominal tergum with white or yellowish-white pile laterally, some black hairs on darker specimens; posterior margin with long, curly, lanceolate white scales. Lateral margins of terga with long, erect, black pile, lanceolate scales and setae medially on two, and anteriorly on three, four, and sometimes five; remainder of lateral margins with black and white setae, and lanceolate and ovate, white, yellow, and sometimes gold scales. Discs of terga two through seven with fine black setae and linear scales, black in medially interrupted transverse bands or spots of varying extent, white along meson, and medially and laterally along posterior margins of all but three and four, yellowish white to reddish brown over remainder. Venter with white or yellowish-white setae and sparse white scales.

MALE GENITALIA (Figure 132).—Gonocoxites broad basally, bilobed apically; apical lobes membranous laterally, separated mesally by deep sulcus; dense, fine hair on lobes and mesally before bases of lobes. Basal segment of gonostylus simple, slightly convex dorsally, with fine hairs apically. Distal segment of gonostylus projecting apicolaterally, with flat basal section from which the apical section curves dorsally and laterally; apex of dorsal section acute or flat and rounded, dorsal margin flat, with ridges, or with preapical tooth; preapical ventral tooth on one specimen. Dorsal part of apex of epiphallus flat, acute basally in lateral view, sharply angled basally in dorsal view; apex broadly rounded in dorsal view, right angled dorsally and broadly rounded ventrally in lateral view. Ventrolateral part of apex of epiphallus extending downward and backward from dorsal part, with sharp ridge curving upward and apically from point below proximal end of dorsal part. Dorsal band unmodified. Base of aedeagus tubular, tapering gradually to junction with ventral bands. Epandrium simple with irregular margins. Cerci narrow, with few setae, with sharp ventral lobe.

FEMALE.—Similar to male.

FEMALE GENITALIA (Figure 125).—Tenth tergum with ten spines on each side. Ventral arm of ninth tergum broad, S-shaped distally, with small, dactylate ventral projection. Dorsal part of sclerite on each side of gonopore produced dorsolaterally as a broad, flat plate with blunt dorsomedial angle, sharp dorsal angle, and broadly rounded ventrolateral angle; ventral arm narrow and curved mesad at tip. Each duct of spermathecae slightly longer than bulb; first section short, clear; second section about as long as bulb, covered with granular pubescence; third section very short; bulb elongate oval, tapering basally to junction with duct.

DISTRIBUTION AND ECOLOGY.—Anthrax trimaculatus has been collected east of the Andes Mountains from Uruguay and northern Argentina to Panama (Map 25). It occurs in a wide variety of habitats, from the caatinga of northeastern Brazil to the grasslands of southern Brazil and the tropical rain forest of Panama. Specimens were collected by the author throughout much of eastern Brazil, usually along paths or near soil or clay banks where bees were nesting.

BIOLOGY.—One reared specimen of this species has been studied. It was reared from the nest of a species of Diadasia (Hymenoptera: Apoidae) by Pe. Jesus S. Moure. The pupa was described previously (Marston, 1964).

TYPES.—The type male of Anthrax trimaculatus Macquart is in the Bigot collection in the British Museum. According to notes by R. H. and E. M. Painter, the right wing and third antennal segments are missing, the head is glued on, and some fungus is present. It carries the label “Anthrax trimaculata nov. sp. Brasil Macq. D. Ex. nom. +.” A photograph and redescription of the type made by the Painters agrees well with specimens from northeastern Brazil. The type-locality given by Macquart is “Brasil.”

The type male of Argyramoeba imitans Schiner is in the Vienna Museum. R. H. and E. M. Painter found it “in good condition except that it is greasy.” It is labeled “Lindig 1864 Venezuela” and “imitans Schin. Alte Sammlung.” A specimen from Corazal, Canal Zone, Panama, agrees with the redescription made by the Painters. They also labeled a specimen from Paraiba, Brazil, as a homotype.

Anthrax trimaculatus Group

The trimaculatus group is a heterogeneous assemblage of species confined to South America, except for one specimen of trimaculatus Macquart collected at Barro Colorado Island, Canal Zone, Panama. Most species may be readily separated from those of the cephus group by absence of setae on the upper half of the face just below the antennae. The one species that has such setae, plurinotus (Bigot), has distinct spots at the bases of cells R4 and M1 (Plate 6a), while those spots are absent in species of the cephus group. The Neotropical species of the oedipus group differ by having short spurs at the medial angles of vein R4 and the m crossvein of the wing, and by having numerous spots along the veins other than at the bases of cells. The species of the tigrinus group may be readily distinguished by the distinctive crossvein between the m crossvein and vein Cu1 on the wing.

No good characters separate the trimaculatus and the albofasciatus groups, but each species of the former has some distinctive characters not found in the latter. Rather than risk confusion by a long statement of variable characters, the group key simply separates the two groups on a geographical basis. They appear to have been derived from a common early Pleistocenic ancestor and to have evolved differences in a variety of characters.

No comprehensive studies of the trimaculatus group have been reported previously, although Edwards (1930) discussed the Chilean species and Stuardo Ortiz (1946) listed them in his catalog of the Chilean Diptera. Nine species are separated in this group; three, baliopteros, latibasis, and caatingensis, are described as new.

Although collections of most major museums in North and South America have been borrowed, only 96 specimens of the trimaculatus group have been obtained, of which 79 are trimaculatus. Thus, all notes regarding distributions and geographic variation are tentative. With further collecting, new species probably will be discovered in areas such as Bolivia, Argentina, and Chile.

Group Description

Body generally black, femora, tibiae, proximal tarsal segments and margins of abdominal sterna and posterior terga often yellow or red. Pruinosity mostly gray or brown, sometimes blue green; eye margins and front with silver pruinosity. Head globoid; eyes separated by 1.0 to 3.0 times width of ocellar tubercle at vertex; antennal sockets separated mesally by about 0.5 their width and about 0.5 to 1.0 of their width from eye margins. Face and lower part of front produced slightly above eye margins; oral margin obtusely angular. Front covered with fine setae and lanceolate scales; lower half and lateral margins of face with setae, setae sometimes present on upper half extending almost to antennae. Occiput with short, semirecumbent setae and sparse, small, lanceolate scales; fringe of pile on posterior margin white to black, usually with lighter tips, some white hairs often present behind vertex. First antennal segment cylindrical or enlarged mesad apically, varying in length from 0.5 to 1.5 times apical width. Second segment globular or greatly flattened apically. Third segment rounded basally, more or less flattened laterally, tapering abruptly or gradually to styliform part, which varies from 0.5 to 1.5 the length of the base; style 0.2 to 1.5 times the length of the styliform part.

Disc of mesonotum with fine black setae and linear, curly scales; scales mixed yellow and white, or forming complex pattern of spots and stripes of white, gold and black scales; lateral and posterior margins with curly white scales. Scutellum with sparse, black setae and linear or lanceolate scales mat are mixed white and yellow, or more commonly, black in submedial spots, white laterally or anteriorly and at apex, and yellow or gold elsewhere. Macrochaetae black or, rarely, more or less red. Sternopleuron, mesopleuron, and anterior part of pteropleuron with white setae and scales, some black setae and yellow or white pile often present dorsally on mesopleuron and pteropleuron. Prosternum, propleuron, and anterior margin of mesonotum with white or yellow pile, some black setae on latter. Postalar tuft of pile white or yellow. Hypopleuron and posterior part of pteropleuron bare. Metapleuron bare or with white scales in patches dorsally and ventrally or directly behind spiracle. Coxae with black, gold, white or mixed, setae and white scales.

Wing (Plate 6a–i) highly variable, largely hyaline or with discrete or coalesced spots at bases of some or all of major cells; rarely with spots at apices of veins M2, Cu1, and Cu2; postmedial spot often present in cell R1. Sectoral crossvein present or absent; when absent, spur at base of cell R4 0.3 to 2.0 times width of base of cell; spur at base of cell R2+3 absent or as much as 2.0 times longer man width of base of cell. Cell 2A well developed with rounded margin, or greatly narrowed with straight margin. Calypter unpigmented, fringe of hairs white. Stem of halter light brown, knob light or dark brown basally, yellow or white apically.

Scales on femora mostly white, some black, or rarely yellow, scales present anterodorsally toward apices, especially on fore and middle pairs. Scales on tibiae black anteriorly and white posteriorly, or sometimes entirely white. Fore femur with incomplete row of macrochaetae anterodorsally; middle femur with anteroventral row (sometimes incomplete); hind femur with anteroventral and sometimes more or less complete posteroventral rows of macrochaetae; scattered bristles sometimes present dorsally toward apex. Tibiae with rows of macrochaetae at all four angles, except anteroventral angle of fore pair.

Discs of abdominal terga usually with scattered black setae and abundant linear or lanceolate scales, rarely with abundant, long black setae and curly, hairlike scales. Black scales present in most species in mesally interrupted bands medially on two and anteriorly on posterior terga, sometimes absent on five, six, and seven; white scales along posterior margins and sometimes on meson; remainder of scales gold or yellow; black scales in continuous bands in squalidus. Pile on lateral margins of first tergum white or yellow; scales on posterior margin white, sometimes dense and curly. Lateral margins of terga two, three, and rarely four with black setae and with black, hairlike to obovate, short or long scales anteriorly and white or yellow scales posteriorly, black scales rarely absent; posterior terga with black setae and white or yellow scales. Venter with sparse, yellow, white, or black setae and linear to obovate white scales.

Gonocoxite of male genitalia (figures 128–137) broad basally, tapering or curving to sharp to broadly rounded apex; apex rounded or flattened, usually with coarse or fine, dense or sparse setae; medial sulcus broad or narrow, with sharp or gradually curved margins. Basal segment of gonostylus simple, platelike, with or without apical setae. Distal segment of gonostylus highly variable, often triangular basally and tapering upward and outward to sharp apex, with various teeth, spines or ridges, sometimes dactylate, ovate and flattened, or with dactylate lateral lobe. Dorsal part of apex of epiphallus highly variable, often with dorsocentral flat plate or spine, deeply emarginate to sharply rounded apically in dorsal view; ventrolateral part broad or narrow, acute or truncate distally; dorsomesal Dorsal band usually with few setae in minimaculatus, with preapical, apically projecting lobe in squalidus. Base of aedeagus bulbous and narrowing abruptly or narrow and gradually tapering to junction with ventral bands before or after junction of dorsal bands. Lateral apodemes of aedeagus open dorsoapically or apically; basal apodeme large, semicircular or circular.

Ninth tergum of female genitalia (figures 122–126) simple, apices of ventral arms acute or slightly expanded with short, curved apical lobe. Tenth tergum with six to ten spines on each side. Sclerite on each side of gonopore hatchet shaped or club shaped; lateral arm broad or narrow, acute or truncate distally; dorsomesal angle sharp, obtuse, rounded or produced as broadly rounded lobe; ventral arm narrow, tapering or parallel sided, and curving slightly mesad. First section of each spermathecal tube short, smooth; second section slightly shorter or slightly longer than bulb, granularly pubescent; third section short, tapering to bulb; bulb oblanceolate or obovate, of equal size.

Taxonomic Characters

The species of the trimaculatus group have undergone a great amount of differentiation so that there are discrete differences between most taxa. The wings of the trimaculatus group (Plate 6a–i) are highly variable between species, ranging from nearly hyaline in squalidus to heavily marked with pigment on the anterobasal portion and at the bases of the posteroapical cells in baliopteros and plurinotus. All species except plurinotus, squalidus, and mystaceus have a distinctive quadrate spot in cell R1 below the tip of vein Sc. Significant variation in the wing pattern has been noted only in trimaculatus and bellulus, but in both it is simply an expansion or contraction of the area of pigment, the extent of which may depend on environmental factors as much as on inherited differences. Specimens of the same species of Anthrax generally have been noted to be darker from wet areas than those from dry areas.

Two species in the trimaculatus group, plurinotus and bellulus, have the posterobasal area of the wing greatly reduced, similar to the species related to argyropygus in the cephus group. The base of cell 2A is almost punctiform and the cell is distinctly narrower than cell 1A; the alula is reduced to a narrow strip of membrane with a straight posterior margin. Again, no species of the albofasciatus group show that character. A complete sectoral crossvein is present in bellulus and latibasis. It often is a somewhat plastic character in other groups, so specimens may lack the crossvein in one or both wings. The sectoral crossvein that Macquart (1840) noted on the wing of mystaceus and that he used as a diagnostic character for the genus Spongostylum is clearly spurious, judging from the figure of the wing. One specimen of mystaceus examined showed the crossvein, and one specimen had a short spur extending anteriorly toward vein R2+3 (Plate 6i) in the same position as the crossvein in Macquart’s figure.

The vesture of the body is similar in all species of the group except squalidus, which has distinctive long black setae on the abdominal dorsum and black and white pile on the sides of the abdomen. Patterns of scales and hairs on the remaining species are essentially similar, although the extent of the colors varies somewhat. However, mystaceus has a distinctive patch of white scales on the metapleuron directly behind the spiracle, and latibasis, bellulus, and minimaculatus have dorsal and ventral patches of white scales on the metapleuron. The alternating tufts of erect, white or yellow and black scales on the sides of abdominal terga two, three, and four are peculiar to trimaculatus, latibasis, minimaculatus, and bellulus.

The male genitalia vary widely interspecifically in the trimaculatus group and are excellent taxonomic characters, as illustrated in figures 128–137. Forms of the apex of the gonocoxite, distal segment of the gonostylus, and the apex of the epiphallus, in particular, are distinctive in each species. Significant variation is found in the structure of the genitalia of trimaculatus, the only species represented by enough specimens to allow a study. The limits, however, are not so wide as to lead to confusion with other species. The female genitalia also vary between species, although less strikingly than in males. Here, the shape of the sclerite on each side of the gonopore is most distinctive. The various structures of the male and female genitalia are named and discussed under the cephus group. The form of the male and female genitalia is not emphasized in keys and diagnoses because there are excellent external characters for separating the species. The externally visible parts of the male genitalia, however, provide an excellent supplementary character to check determinations.