Zethus (Zethoides) thoracicus Fox, 1899

Lopes, Rogério Botion & Melo, Gabriel A. R., 2025, New nests of Zethus reveal unexpected architecture variation in the olmecus species group (Hymenoptera, Vespidae), Revista Brasileira de Entomologia (e 20240126) 69, pp. 1-9 : 3-5

Zethus (Zethoides) thoracicus Fox, 1899

Nest 1

Collecting data: collected in 24.viii. 1991 in the Reserva Ducke, Manaus. The nest was found suspended by a fine root in a small earth bank. There were six females in the nest at the time of collecting. Cell content was not examined.

Overall aspect ( Figs.4 A-4C): The nest consisted of an approximate spherical structure, bearing a dome made of cut leaves on the upper part. Unfortunately, no details about the dome were taken at the time of collecting and desiccation of the leaves led to its rapid fragmentation. The lower portion of the nest remained mostly intact and comprised a group of vertically oriented and adjacent brood cells, all aligned parallel to the root, with their opening directed upwards. Laterally and in the bottom, the cell set was surrounded by layers of leaf fragments, similar to those making up the dome.

Fixation: the nest used a ramified root as substrate, with two more robust segments and several thin, more delicate segments which were broken, but previously continued into the nest. The more robust portions appear to be the main support of the nest, one in each side of an outermost cell of the cluster (third cell of the second row). The root reemerged from the nest below, making a loop under it.

Brood cells: total of 25 cells, arranged in six rows with 3, 3, 7, 5, 4 and 3 cells. This arrangement in rows is indicated here simply for mapping purpose and does not imply the order in which they were built. The second row presents a cavity that superficially resembles a cell, but closer examination reveals it is not, as it does not possess the typical concentric walls and it is much shallower than the cells. Cell openings are circular to ellipsoid. Cell walls are built with a finely macerated material ( Fig. 4D ), which is impossible to determine foliar structure beyond some sparse trichomes. Borders of some openings may present small leaf fragments.

Cover: we refer here basically to the layers covering the lower portion of the nest around the cell set. It comprised of cuttings of foliage arranged in several layers. Leaf fragments were majorly strips with few fragments presenting short and/or irregularly shapes ( Fig. 4E ). The material presents leaves of different morphology regarding trichomes, which when present can be restricted to veins or along the whole fragment. Also, coloration and vein pattern of leaves vary. Most fragments present one serrated margin, usually along the length of the fragment, that indicates where the leaves were cut by the wasp. The “teeth” of these serrations are curved. Leaf fragments appear to be randomly arranged, glued together only at some points, rather than the entire extent and so leaving wide spaces between each strip.

Measurements: Root: length above nest = 9 cm; ramification until nest attachment = 4.43 cm; length inside nest = 2.61 cm. Nest: greatest length = 47.53 mm; greatest height = 37.49 mm. Cell area: greatest length = 51.94 mm; greatest width = 29.43 mm. Cell depth = 18.16 mm ± 2.16 mm; cell opening diameter = 3.92 mm ± 0.27 mm. Leaf cover of variable width: greatest width = 18.07 mm; smallest width = 3.36 mm. Leaf fragments: greatest length 9.1mm; smallest length = 3.3 mm; greatest width = 2.9 mm; smallest width = 0.8 mm. Length/width ratio of leaf fragments: greatest = 9.1; smallest = 2.5.

Figures

Figure 4. Nest of Zethus thorcacicus. A) Overhead view. B) Oblique view. C) Lateral view. D) Closeup of nest, showing finely macerated matter comprisinf cells (left) and larger leaf fragments comprising the cover (right).E) Examples of leaf fragments detached from the nest:without trichomes (left);completely covered in trichomes (middle); trichomes only on midrib (right).