Zethus (Zethus) pilosus Zavattari, 1912

Lopes, Rogério Botion, Brozoski, Franciele & Buschini, Maria Luisa Tunes, 2019, Zethus (Zethus) pilosus Zavattari, 1912 (Hymenoptera: Vespidae: Eumeninae) from Southern Brazil: description of the female, the male genitalia, its nest and notes on biology, Zootaxa 4648 (1), pp. 187-193 : 188-192

Zethus (Zethus) pilosus Zavattari, 1912

Zethus pilosus Zavattari, 1912: 10 (key), 64 (male). Bohart & Stange, 1965: 24 (endemic to Southeastern Brazil), 113 (key), 115 (male).

Diagnosis. Dorsum of pronotum punctate, with humeral edge raised and inter-humeral width clearly smaller than inter-tegular width ( Fig. 5 ). Submedian propodeal carina not developed as membrane. Stem of T1 well defined ( Fig. 6 ).

Description. Female. Ground-color black. Yellow markings as follows: basal half of mandibles, one apical and a pair of lateral spots on clypeus, pair of spots above antennal sockets, spot on ocular sinus, pronotal lobe, parategulae and apical bands on S3-6. Reddish markings as follows: ventral surface of F-VI to XII, mandibles apically, posterior margin of pronotum, fore and mid legs, hind tibiae and tarsi, tegulae, lateral spots on metanotum, longitudinal bands on lower half of propodeum, T1 ventrally, apical bands on T1-2, apical band on S2. Wings hyaline with amber costa.

Frons, vertex and scutum strongly striate. Clypeus striato-punctate. Occipital carina complete dorsally and ventrally. Hypostomal carina complete, straight and forming angular junction with occipital carina. Pronotal carina lamellar. Pronotum and mesopleura moderately to densely punctate. Dorsal suture of mesepisternum present. Scutellum and metanotum sparsely punctate. Discoid puncture elongated, surrounded by smooth area. Propodeum coarsely reticulated with complete submedian and lateral carinas and coarse transverse striae medially. Metasomal terga densely micropunctate, T1 with moderate macropunctation. Sub-basal carina absent. Anterior margin of S1 elliptical. Metasomal sterna very sparsely punctate, S2 smooth basally. Gradulus present in T3 and S3.

Clypeal apex straight, as wide as interantennal breadth with no evident teeth. Palpi formula 6:4. Gena wide with margin slightly sinuous. Pronotal carina sinuous in lateral portion. Pronotum with subhumeral area long, over three mid ocellus diameters. Humeri edged anteriorly and forming a raised margin, rounded on posterior third. Pronotum narrower anteriorly in dorsal view. Fore basitarsus with multiple spines on outer surface. Parategula digitiform. Mid tibia without spines and with only one apical spur. Metanotum not tuberculate. Row of spines in hind tibiae. Dorsal propodeal aperture slender, slit-like. Apical propodeal lamella developed, quadrangular. Propodeal orifice oblong. Propodeal valvula rectangular, free apically. T1 with evident stem and expanded portion narrow, not more than twice as wide as stem and apical constriction very weak. Lateral margins of T1 not touching ventrally. S1 flat, not constricted into carina. Stem of T2 very short. S2 regularly convex. Apical lamella developed in T2-5 and S2-5. S6 with crown of spines apically. Fore wing length: 12 mm.

Long, golden and erect pilosity throughout entire body, denser on metasoma, where a shorter, but very thick tomentum is also present.

Variations. The reddish and yellow markings vary, sometimes smaller or absent in some specimens. The female is highly similar to the male, the latter having lighter and more extensive pale markings besides the typical dimorphisms (shape of clypeus, number and shape of flagellomeres and apparent metasomal terga).

Comments. Features of the pronotum are major components in the diagnosis of this species. The punctures of this sclerite ( Fig. 5 ) in Z. pilosus differ from other species that are mainly striate ( Fig. 7 ). The incomplete oblique carina on the pronotum used by Bohart and Stange (1965) does not correspond to an actual carina, but rather the angled (or “bent” used by Bohart and Stange) humerus which is slightly raised, forming a margin ( Fig. 5 ), rather than being a simple edge ( Fig. 7 ). The fact that it is punctate supports the idea of not being a carina. Finally, the widening aspect of the pronotum in dorsal view, making the humeral angles obtuse ( Fig. 5 ), differs from the straightness in other species, where the humeral angles have the same width as the posterior end of the sclerite in dorsal view, making the humeral angles nearly straight ( Fig. 7 ).

The well-defined stem of T1 is apparently shared by only one other species, Z. cataractae Cooper, 2010 , which was not examined, but also serves as a good character to differentiate the taxa, since the other species present a poorly differentiated petiole ( Fig. 8 ).

Male genitalia. Aedeagus ( Figs. 9, 10 ) with basal plate triangular and short, not reaching tip of apodemes. Apodemes with flat base and strong projection on ventral surface of the curvature. Ventral lobe long and rectangular, higher basally, with ventral margin reflexed outwards, more so anteriorly. Head simple, without any indents or indication of bilobation.

Gonocoxite ( Fig. 11 ) approximately 2.7 times as long as wide with rounded apex. Apical half of ventral margin with short (medially) to long (apically) pilosity. Gonostylus long and straight, originating on dorsal margin of gonocoxite in about half of its length.

Volsella ( Fig. 11 ) with crest straight and rather narrow. Digitus with long pilosity, basal lobe wide and long, strongly projected basally and distal lobe also long, but narrow. Cuspis triangular with very long and thin basal projection; root clearly visible, digitiform; medial lobe weakly projected, marked by conules.

The overall structures of the male geniatalia are highly similar to those of Z. strigosus (fig. 290, p. 201 in Bohart and Stange 1965). Still, two main differences stand out for Z. pilosus : the narrower distal lobe of the digitus and the longer ventral lobe of the aedeagus.

Nest. Four nests of Z. pilosus were collected, one of which was in association with a spider-wasp, Auplopus sp. ( Pompilidae , Pepsinae ), where the two posterior-most cells were of Z. pilosus and the three anterior cells used by the pompilid. The female wasps did not nest in any of the bamboo traps, only in blocks with openings of 7.0 and 10.0 mm.

Nests were formed from one to four cells in linear disposition and may present a vestibular cell. Each cell was provisioned with caterpillars and closed by a partition ( Fig. 12 ), which was built in a single layer with a rugose con- cave inner surface and a smooth convex outer surface. These were composed of macerated vegetable fibers mixed with resin, mud and grains of sand. Parts of other insects (apparently ants), such as antennae, heads and legs were also used. The mud varied in coloration, from dark brown to reddish. While building, the female made a partition in the opening of the nest with a small central orifice, just big enough for her to go through ( Fig. 13 ), which was left opened when the nest was concluded. Cocoons of the larvae were nearly translucid, shiny and white, firmly adhered to the nest walls and was woven in a manner such that the meconium was left apart from the pupa ( Fig. 14 ).

The nesting of this species is typical of wasps presenting solitary behavior, occupying pre-existing cavities and mass provisioning, similar to that of Zethus dicomboda ( Claude-Joseph, 1930) . While the biology is known for fewer than 20 species of Zethus , other similarities include the egg being laid in the roof of the cell, as reported for Z. laevinodus and the use of vegetable matter for construction, widespread in the genus ( Bohart & Stange, 1965). However, the division with the central orifice, the use of combined mud and sand (and not just vegetable matter) and use of insect parts are unique when compared to known nests of other members of the genus. The mixture of soil and plant fibers has been reported in the zethines Raphiglossa and Psiliglossa ( Ferton, 1911, 1921), but this is clearly a convergence and not a shared apomorphy.

Biology. Development from egg to adult took an average of 39 days to be completed (considering the day the nest was collected to the emergence of the adults). Nests were founded between late December and early April, leading to two hypotheses: diapause during winter takes place in the adult stage and not in the larval stage; and these wasps are at least bivoltine.

Examined material. 7♀, 2♂.

‘Brasil, PR, Guarapuava\ Vale do Jordão\ 25º26’24”S e 51º26’30”W \ 2018\ Brozoski, F. \\ N 362\ 14/02/2018 \ 12/03/2018 ’[2♂, 2♀, UNICENTRO]. Same data ‘ 25º26’55”S e 51º27’06”\ 2017/2018\ Brozoski, F.\\ N: 960\ 27/12/2017 \ 30/01/2018 ’ [1♀, UNICENTRO]. Same data ‘2018\ Brozoski, F.\\ N 243\ 04/04/2018 \ 04/04/2018 ’ [1♀, UNICENTRO]. Same data ‘N: 569\ 30/01/2018 \ 30/01/2018 ’ [1♀, UNICENTRO]. Same data ‘N: 569\ 30/01/2018 \ 06/03/2018 ’ [1♀, UNICENTRO]. ‘Nova Teutonia\ Santa Catarina \ BRAZIL, Jan 19 66 \ Fritz Plau- mann’ [1♀, AMNH].

Figures

FIGURES 5–8. Diagnostic characters of Zethus pilosus and corresponding traits in Zethus strigosus. 5-6. Zethus pilosus. 7-8. Zethus strigosus. 5, 7. Pronotum (pnt) and mesoscutum (msct), dorsal view. 6, 8. First metasomal tergum, dorsal view. Arrow indicates stem. Scales: 1.0 mm.

FIGURES 9–11. Male genitalia of Zethus pilosus. 9. Aedeagus, ventral view. 10. Aedeagus, lateral view. 11. Gonocoxite, gonostylus and volsella, inner view; cuspis shaded in gray. Scale: 1.0 mm.

FIGURES 12–14. Nest of Zethus pilosus. 12. Overall nest architecture. A. Vestibular cell. B. Part of cocoon adhered to the wall. C. Partition closing the nest. D. First cell containing larva and prey. E. Larva in late developmental stage. 13. Front-end view of nest showing outermost partition with central orifice. 14. Cell presenting meconium (brown) isolated, outside of cocoon (white).