Two nests of Celonites jousseaumei were found at Ait Daoud (WGS 84: 29°36.977'N, 08°59.009'W), 15 km south of Tafraout in the Antiatlas in Morocco, situated at a height of 1140 m a.s.l. The climate of the area is arid with a mean annual precipitation of 235 mm and a mean annual temperature of 16.6 °C (data from Tafraout, AM ONLINE Project). The habitat consisted of a richly flowering roadside (Fig. 1b) with adjacent former terraces of almond orchards that were left fallow since approximately ten years because of increasing aridity (Fig. 1a). The stony area was heavily grazed and somewhat polluted with rubbish, i.e. along little dry drainage channels.

In the area Celonites jousseaumei and C. pictus were recorded. Imagines of both species were exclusively observed to visit flowers of Heliotropium crispum Desf. (number of sightings at H. crispum flowers: C. jousseaumei 1♂ 3♀, C. pictus 66♀), although other plants were flowering at the site, for example Cladanthus arabicus (L.) Cass., Centaurea calcitrapa L., Pallenis spinosa (L.) Cass., Senecio glaucus subsp. coronopifolius (Maire) C. Alexander (all Asteraceae), Echium horridum Batt. (Boraginaceae), Lotus sp. (Fabaceae) and Convolvulus trabutianus Schweinf. & Muschl. (Convolvulaceae).

Figure 1. 

a, b habitat of Celonites jousseaumei at Ait Daoud, 15 km south of Tafraout, Morocco a nest site b foraging area c exterior view of nest B d, e stones used as base for nests of C. jousseaumei d nest N e nest B.

Both nests were situated at the steep edge of a 0.5 m high terrace with an exposure of 70° to the north (ENE) (Fig. 1a). The site was approximately 10 m away from large patches of Heliotropium crispum flowering on the embankment of the road (Fig. 1b). Both nests were attached to almost vertical surfaces of medium sized stones (Table 1, Fig. 1d, e), 6 cm and 29 cm respectively above the foot of the terrace. The distance between the nests was 75 cm.

The nests were made of fine clayey soil with a small proportion of tiny stones and consisted of 2 or 3 cells (Table 1). The cells were arranged in a longitudinal row in which each subsequent cell abutted with its basal end onto the apical end of the completed preceding cell. The resulting almost vertical or diagonal linear construction was 15.5 mm or 20.9 mm long, with the apical ends of the cells oriented downward (Figs 1c, 2a). An additional nest covering was not present. This exclusively linear arrangement of the brood cells is in congruence with the fragmentary nest description of Celonites jousseaumei senegalensis by Richards (1962). Linearly arranged brood cells were also observed in a few nests of C. abbreviatus (Lichtenstein 1869) and C. fischeri (Mauss & Müller, 2014), but in these nests at least a single cell was also attached longitudinally to the others in addition. Moreover, in most nests of C. abbreviatus (Bellmann 1984) and C. fischeri (Mauss & Müller, 2014) the cells are only attached longitudinally to each other, which is also the case in all of the few known nests of other members of the C. abbreviatus-group, in particular C. tauricus (Mauss et al. 2016) and C. mayeti Richards, 1962 (Lichtenstein 1875). Therefore, the observed exclusively linear arrangement of the brood cells of C. jousseaumei is of note.

The brood cells were cylindrical with almost parallel sides, rounded at the basal and truncate at the apical end (Fig. 2b, c). The median dimensions of the cells were: outer length 7.3 mm (n = 5), outer diameter 3.6 mm (n = 5), inner length 6.3 mm (n = 4), inner diameter at the cell opening 3.4 mm (n = 4) (Table 2). The outer cell surface showed a distinct “fish scale” pattern (Figs 1c, 2a) while the inner surface was smooth (Fig. 2c). Towards the stone it was attached to, the cell wall was not completely constructed resulting in a few spots in the median axis where the surface of the stone formed the boundary of the cell (Fig. 2c). The outer cell wall continued between adjacent cells laterally covering the small hollow space between them that resulted from the existence of two separate cell walls that is the transversal apical wall of the basal cell and the rounded basal wall of the apical cell (Fig. 2b, c). At the apical end of the nest the outer wall of the last cell was produced into a small rim protruding the apical transversal cell wall by 2.1 mm (Fig. 2b). The wall of the rim had one or two deep notches and was slightly bent outwards (Fig. 1c). Within this short tube-like entrance, the nest was sealed by a circular, curved, circa 0.2–0.3 mm thick mud plug (Fig. 2b). This nest seal was positioned about 0.2 mm above the apical wall of the last cell and 1 mm inwards from the edge of the nest opening resembling the bottom of a new cell in form, position and structure.

Figure 2. 

Structure of Celonites jousseaumei nest N on 19^th of April: a exterior view b brood cells opened in longitudinal direction c cell content removed. (N1–N3 = brood cell numbers; aw = apical cell wall; bw = basal cell wall; e = egg; hs = hollow space below pollen loaf; l = larva; nr = nest rim; ns = nest seal; p = pollen loaf; pa = papilla on surface of pollen loaf; s = bare stone surface; measurements and cell content summarized in Table 2).

Figure 3. 

Neighbour joining tree of COI-5P sequences of 9 imagines of Celonites (Masarinae) from Morocco, 10 imagines of Spintharina (Chrysididae) and 2 immature stages collected from brood cells of two Celonites nests from Morocco (see text for details).

The content of the brood cells is summarized in Table 2. The provision consisted of a yellowish-white, viscous pollen mass with shining surface forming a pollen loaf. The surface of the loaf was characteristically papillated (Fig. 2b) so that it barely touched the cell walls. Between the apical end of the pollen loaf and the apical wall of the cell remained a hollow space measuring approximately 0.8–0.9 mm (Fig. 2b). Inwards the pollen mass became more sticky and rather liquid, so that it could not be removed as a whole with a pair of tweezers. The provision in the cells of both nests consisted exclusively of Heliotropium pollen indicating narrow oligolecty (sensu Müller and Kuhlmann 2008) of C. jousseaumei at this locality. Both eggs of Celonites jousseaumei were whitish and curved. Each egg was situated on top of the provision close to the basal end of the cell indicating that it was laid by the female prior to brood cell provisioning (Fig. 2b). Small remnants of membranous material attached to one pole of each egg suggested that the eggs had initially been attached to the wall. The small larva from cell N1 was also situated basally on top of the pollen mass, where it fed on the provision (Fig. 2b).

The COI-5P gene sequence of the larva from brood cell N1 was 100% identical (distance of 0) to the sequence of a Celonites jousseaumei female [CECYP037-22] collected northeast of Sidi Ifni at a distance of approximately 100 km from the nest site. Four additional specimens of C. jousseaumei from Morocco were sequenced; the average within-species genetic distance among these specimens was 0.51% (minimum 0, maximum 1.19). The sequence of the larva from brood cell N1 to C. pictus [CECYP004-20] was 24.25%. In the distance-based tree (Fig. 3), the larva N1 clusters together with the imagines of C. jousseaumei. Therefore, it can be concluded that the recorded nests belong to C. jousseaumei. This is in congruence with the cell dimensions that are too small for C. pictus but match the size of C. jousseaumei (median total length of females 7.46 mm (n = 8) in C. pictus versus 5.75 mm (n = 7) in C. jousseaumei).

The pupa from brood cell B2 turned out to belong to a species of Chrysididae, as the obtained COI-5P gene sequence of the pupa closely matched the public sequences of Spintharina versicolor Spinola, 1808 within BOLD database. However, the identity of the sequences was only 92%, indicating that the pupa belongs to a different but related species. After additional sequencing of the reference chrysidid specimens from Morocco, a match was found between the pupa and a specimen of Spintharina innesi collected in Tizourgane [CECYP026-22] (Fig. 3). Three additional specimens of Spintharina innesi were sequenced; the average within-species genetic distance was 0.71% (minimum 0.33, maximum 1.31). The genetic distances between the pupa from brood cell B2 and Spintharina procuprata or Chrysis patruela were 17.20% and 12.13%, respectively. Therefore, it can be concluded that Celonites jousseaumei is a host of Spintharina innesi. Host-parasite associations of Spintharina with Celonites seem to be common. In Europe Spintharina versicolor has been recorded as a brood parasite of Celonites abbreviatus (Blüthgen 1961; Erlandsson 1972), while in the Afrotropical Region Spintharina arnoldi (Brauns, 1928) and Spintharina bispinosa (Mocsáry, 1902) were reared from brood cells of two different Celonites species (Brauns 1913; Gess 1996). Moreover, Pauli et al. (2019) found a close phylogenetic relationship between Spintharina and the Nearctic Chrysurissa, which also appear to parasitize exclusively pollen wasps. This phylogenetic placement indicates that both genera are descendants of a last common ancestor which may already have exploited pollen wasps as hosts, suggesting an old and exclusive association with pollen wasps in this clade. However, the host specificity of numerous Spintharina species is poorly known and it remains to be shown whether Spintharina innesi is restricted to C. jousseaumei or if it may also parasitize brood cells of other species of Celonites or even of other pollen wasp genera. Conversely, there are at least three other species of Spintharina recorded from Morocco that are all suitable in size to fit the brood cells of C. jousseaumei (cf. Linsenmaier 1999, classified as species of the Chrysis versicolor-group), so that this pollen wasp may be parasitized by more than one Spintharina species.