Foraging Behavior of Two Pollen Wasp Species of the Genus <i>Celonites</i> Latreille, 1802 (Hymenoptera: Vespidae: Masarinae), from the Altai Mountains

<i>Celonites kozlovi</i> Kostylev, 1935, and <i>C. sibiricus</i> Gusenleitner, 2007, coexist in semi-deserts of the Altai Mountains. The trophic relationships of these pollen wasp species to flowers are largely unknown. We observed the flower visits and behaviors of wasps on flowers; pollen-collecting structures of females were studied using SEM; the taxonomic position of these two species was ascertained with the barcoding sequence of the mitochondrial COI-5P gene. <i>Celonites kozlovi</i> and <i>C. sibiricus</i> form a clade together with <i>C. hellenicus</i> Gusenleitner, 1997, and <i>C. iranus</i> Gusenleitner, 2018, within the subgenus <i>Eucelonites</i> Richards, 1962. <i>Celonites kozlovi</i> is polylectic in the narrow sense, collecting pollen from flowers of plants belonging to five families (with the predomination of Asteraceae and Lamiaceae) using diverse methods for both pollen and nectar uptake. In addition, this species is a secondary nectar robber, which has not been observed in pollen wasps before. The generalistic foraging strategy of <i>C. kozlovi</i> is correlated with an unspecialized pollen-collecting apparatus on the fore-tarsi. In contrast, <i>C. sibiricus</i> is broadly oligolectic, predominantly collecting pollen from flowers of Lamiaceae. Its specialized foraging strategy is associated with apomorphic behavioral and morphological traits, particularly specialized pollen-collecting setae on the frons, which enable indirect pollen uptake using nototribic anthers. These adaptations in <i>C. sibiricus</i> evolved independently of similar specializations in the <i>Celonites abbreviatus</i>-complex. <i>Celonites kozlovi</i> is re-described, and males are described for the first time.