Notes on two nests of Ancistrocerus oviventris (Wesmael, 1836), with new records of its prey and brood parasites (Hymenoptera: Vespidae: Eumeninae)

Abstract Two nests of Ancistrocerus oviventris (Wesmael, 1836) are described. One nest from Poland was attached to a concrete fence and consisted of 10 mud cells. The second nest from the Crimea was attached to a stone and consisted of three mud cells covered with an additional layer of mud and gravel particles. Females provisioned their cells with moth caterpillars of the families Crambidae and Depressariidae; 5–13 caterpillars were stored per cell. A chalcid wasp Monodontomerus aeneus (Fonscolombe, 1832) was recorded as a parasitoid while a cuckoo wasp Chrysis rutiliventris Abeille, 1879 and a sarcophagid fly Amobia sp. were recorded as kleptoparasites.


Material and methods
The first nest was found in the town of Kowalewo Pomorskie in Poland (53°10'05"N, 18°52'15"E) and observed on 9-22 June 2022 during sunny and warm days. The site in Kowalewo Pomorskie comprised a backyard surrounded by fallow land overgrown with herbaceous vegetation (see Olszewski et al. 2021 for details). Another nest was found in the Kanaka Reserve in the Crimea (44°46′28″N, 34°37′01″E) on 8 June 2015. This site was a stony beach at the coast of the Black Sea. Species identification was done after catching females with an entomological net. Nesting biology was analysed based on direct observations and on-site notes. Photographs were taken with a Canon EOS M50 and a Canon PowerShot SX160 IS cameras; in addition, a Raynox M-250 macro converter was used. The contents of the cells were collected after detaching the nests from the substrates on 22 June in 2022 and 8 June in 2015.

Results
The nest from Kowalewo Pomorskie consisted of 10 mud cells placed in a milled recess on a concrete fence ( Figure 1). Nine cells were arranged in three rows of three cells each ( Figure 2); the 10 th cell was incomplete and corresponded to the beginning of the fourth row (the nest was not finished). The female of A. oviventris observed at this nest was usually building a new cell from mud (soil mixed with regurgitated water and saliva) in the afternoon (until approximately 4 pm) so that the provisioning happened mostly in the morning. After a cell had been sealed with a mud plug, the female constructed the next cell in the same row or began a new row of cells. The cells were 7-8 mm in inner diameter and 9-10 mm in inner length. The female provisioned cells with moth caterpillars of the subfamily Crambinae (Lepidoptera: Crambidae) (Figure 3), 6-13 caterpillars were stored per cell depending on their size (10 on average). The female carried them to the nest by flight at intervals of about 12-25 min. While the female was away from the nest, a cuckoo wasp belonging to the Chrysis ignita-group was observed entering a cell (Figure 7), but its progeny were not found in the nest. During the nest inspection on 22 June 2022, a total of six A. oviventris larvae at different stages of development were collected from six cells ( Figure 5). Three remaining complete cells were infested with numerous pupae and imagoes of Monodontomerus aeneus (Fonscolombe, 1832) (Hymenoptera: Torymidae) (Figures 8, 9).
The nest from the Kanaka Reserve was located in a crevice of a medium sized stone. This nest contained three irregularly arranged mud cells covered with an additional layer of mud and gravel particles ( Figure 6). The female of A. oviventris was observed only in the moment when she finished this additional covering. The cells were 7 mm in inner diameter and 14-20 mm in inner length. The first (the most inner) cell contained four maggots of a kleptoparasitic fly Amobia sp. (Diptera: Sarcophagidae). The second cell contained seven stored moth caterpillars, a dead  wasp egg, and a young larva of a cuckoo wasp (Hymenoptera: Chrysididae). The third cell contained five stored caterpillars and a wasp egg. The caterpillars were of the family Depressariidae (Lepidoptera) with predomination of two species tentatively identified as Agonopterix pallorella (Zeller, 1839) and Exaeretia stramentella (Eversmann, 1844) ( Figure 4). The cuckoo wasp reared from the second cell was identified as Chrysis rutiliventris Abeille, 1879.

Discussion
The results of the presented research are largely consistent with the literature. Particularly, the structure of the nests of A. oviventris observed in this study corresponds to earlier descriptions (e.g., Mjöberg 1909;Micheli 1930;Nielsen 1932). Our data, however, specified the taxonomic composition of the prey of this species: previous researchers suggested that it was (unspecified) moth caterpillars (Ferton 1895;Nielsen 1932;Bonelli 1970) or caterpillars of the family Tortricidae (Mjöberg 1909;Micheli 1930) while we found them belonging to Crambidae and Depressariidae. Supposedly, the earlier researchers merely did not separate two latter families from the family Tortricidae in the broad sense. However, it is also highly possible that A. oviventris can hunt for the true Tortricidae as well. When analysing the prey of A. oviventris, we can also suppose that females of this species hunt for caterpillars at the grass level. Both tentative prey species identified from the Crimea, A. pallorella and E. stramentella, are confined to herbaceous Asteraceae: Centaurea spp. and Tanacetum spp., respectively (V.V. Savchuk, personal communication). Reports of beetle larvae (both Curculionidae and Chrysomelidae) as the provision of A. oviventris by Borries (1897) and Blüthgen (1961) seem erroneous due to misidentified wasps. Ancistrocerus oviventris was reported as a host of C. rutiliventris by Morgan (1984). However, this species of cuckoo wasps is replaced in the Great Britain by the closely related C. vanlithi Linsenmaier, 1959 (P. Rosa, personal communication). Therefore, the report by Morgan (1984) referred to C. vanlithi but not to C. rutiliventris. Thus, our record of the host-parasite relationships between A. oviventris and C. rutiliventris is actually new. Since the larva of this cuckoo wasp apparently  killed the host egg and then was observed feeding on the stored provision, it can be assumed that this species acts as a kleptoparasite (= inquiline) (see the classification in Martynova & Fateryga 2015).
In this study, we recorded Amobia sp. and M. aeneus for the first time as brood parasites of A. oviventris. The first species fed mostly on the prey and thus, similarly to C. rutiliventris, is a kleptoparasite. Monodontomerus aeneus fed on the host prepupae and thus is a parasitoid. In the literature to date, M. aeneus has apparently only been mentioned among parasitoids of the bees in the families Apidae and Megachilidae (Grissell 2007).