Abstract
Celonites kozlovi Kostylev, 1935, and C. sibiricus 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. Celonites kozlovi and C. sibiricus form a clade together with C. hellenicus Gusenleitner, 1997, and C. iranus Gusenleitner, 2018, within the subgenus Eucelonites Richards, 1962. Celonites kozlovi 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 C. kozlovi is correlated with an unspecialized pollen-collecting apparatus on the fore-tarsi. In contrast, C. sibiricus 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 C. sibiricus evolved independently of similar specializations in the Celonites abbreviatus-complex. Celonites kozlovi is re-described, and males are described for the first time.