Chelostoma ( Chelostoma ) florisomne (Linnaeus, 1758)

Müller, Andreas, Pisanty, Gideon & Dorchin, Achik, 2025, Western Palaearctic Chelostoma bees of the subgenus Chelostoma (Megachilidae, Osmiini): biology, taxonomy and key to species, Zootaxa 5717 (3), pp. 329-369 : 339-340

Chelostoma ( Chelostoma) florisomne (Linnaeus, 1758)

Apis florisomnis Linnaeus, 1758: 577 . Type material: Lectotype ♂, by designation of Day (1979), “in Europa” ( Sweden), The Linnean Collections of the Linnean Society London. Type species of Chelostoma Latreille.

Apis maxillosa Linnaeus, 1767: 954 . Type material: Holotype ♀, “in Europa” ( Sweden), The Linnean Collections of the Linnean Society London. Synonymy in Kirby (1802).

Chelostoma culmorum Lepeletier, 1841: 408 . Type material: Syntypes ♂ ♀, type depository unknown. Synonymy in Schwarz et al. (1996).

Heriades parumcrinitus Alfken 1932: 113 . Type material: Holotype, ♀, “Ebelsbach am Main” ( Germany), Museum für Naturkunde Berlin. Synonymy with Heriades maxillosus (Linnaeus) in Benoist (1945).

Literature records. Outside Europe: GEORGIA: Kvemo Kartli, Samzche-Dschawachetia, Tbilisi ( Kirkitadze and Japoshvili 2015). TURKEY: Ankara, Artvin, Bolu, Erzurum, Konya, Samsun, Yozgat ( Özbek 2011).

New records. Outside Europe: ARMENIA: Tawusch: Dilidschan , 5.6.1998, 1♂ (leg. Beenai). GEORGIA: Kvemo Kartli: Manglisi, 14.6.2015, 1♂ (leg. M. Snizek) .

Distribution. Almost entire Europe (except for Iceland, Ireland, Scotland, Fennoscandia north of 63° northern latitude as well as all Mediterranean islands, such as Balearic Islands, Corsica, Sardinia, Sicily, Crete or Cyprus), Turkey and Caucasus ( Armenia, Georgia). The species is known from the following European countries: Albania, Andorra, Austria, Belarus, Belgique, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Denmark, Estland, Finland, France, Germany, Greece, Hungary, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Moldova, Netherlands, Norway, Poland, Portugal, Romania, central and southern European Russia, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Ukraine including Crimea, United Kingdom ( Reverté et al. 2023).

Pollen hosts. Oligolectic on Ranunculus ( Ranunculaceae ) ( Westrich 1989; Sedivy et al. 2008). The females collect the pollen of Ranunculus by rapidly tapping their metasomal scopa against the anthers in a sideways body posture. To supply a single brood cell, the entire pollen content of about ten flowers of Ranunculus acris is needed ( Müller et al. 2006). In a capture-recapture study, pollen-collecting females exploited Ranunculus stands up to 650 m away from the nest, crossed forests up to 480 m wide and overcame differences in altitudes of more than 130 m on their flights between nest and feeding habitats; the latter seems particularly impressive as the females had to fly uphill 10–15 times a day to reach the nest with a full load of pollen, which can account for up to a seventh of their entire body weight ( Zurbuchen et al. 2010). In very rare and exceptional cases, the females were observed to collect pollen also on other plants, such as Fragaria and Rosa ( Rosaceae ) or Stellaria ( Caryophyllaceae ) ( Käpylä 1978; Schulze et al. 2012). In fact, experiments showed that the larvae can also develop on pollen of Campanula ( Campanulaceae ) and Brassica ( Brassicaceae ), suggesting a certain flexibility to use other pollen sources when Ranunculus flowers are not available; in contrast, development on the pollen of Tanacetum ( Asteraceae ) proved to be impossible ( Praz et al. 2008).

Nesting biology. C. florisomne nests in narrow linear cavities with a diameter of 3–5.5 mm, such as insect burrows in dead wood, hollow plant stems (e.g. Phragmites ), artificial borings in wood and stems or more rarely in abandoned nests of aculeates in clay walls or in glass tubes ( Bonelli 1967, 1968; Brechtel 1986; Käpylä 1978; Maréchal 1933; Rozen & Praz 2016; Ruszkowski et al. 1995; Van Lith 1957; Westrich 1989). The nests contain 1–10, in exceptional cases up to 27 linearly arranged brood cells, which are often interrupted by short empty spaces. An empty vestibule is usually present between the outermost brood cell and the nest plug. The partitions between the brood cells and the nest plug consist of mud, which is mixed with nectar and possibly also salivary secretions as a binding agent. The construction of the thin cell partitions requires only 3–5 material transport flights and takes only a few minutes. In contrast, several hours may be needed to build the thick nest plug, in which small pebbles, sand grains, small snail shells or other particles are typically embedded on its outside. C. florisomne overwinters as an uncoloured or more rarely as a coloured pupa in a self-spun cocoon within the brood cell. Metamorphosis to the imaginal stage takes place after the first winter with some of the individuals undergoing a twoyear development. Reported larval parasites are Chrysis ignita (L.), Chrysura austriaca (Fabricius) and Trichrysis cyanea (L.) ( Hymenoptera , Chrysididae ), Eurytoma nodularis Boheman ( Hymenoptera , Eurytomidae ), Melittobia acasta Walker ( Hymenoptera , Eulophidae ), species of Ephialtes and Townesia ( Hymenoptera , Ichneumonidae ) and Trichodes alvearius (Fabricius) ( Coleoptera , Cleridae ) ( Maréchal 1933; Berland & Bernard 1938; Van Lith 1957; Westrich 1989). Known food parasites are Monosapyga clavicornis (L.) and Sapyga quinquepunctata (Fabricius) ( Hymenoptera , Sapygidae ) as well as Gasteruption jaculator (L.) ( Hymenoptera , Gasteruptionidae).

Male mating behaviour. The males patrol the flowers of Ranunculus in rapid flight in search of females; at the beginning of the flight period, they also visit (potential) nesting sites in order to mate with hatching females ( Käpylä 1978; Westrich 1989). The males possess a dense tuft of short whitish to yellowish hairs on the lowermost part of the genal area near the mandibular base; this specialised pubescence likely plays a role in mating behaviour, as it is often soaked with a liquid of unknown origin, which might serve to mark flight areas or be used for inter-sexual communication during courtship and mating.

Note. A male from the province Bolu in Turkey (“ Bolu lake env., 28.4.1994, leg. M. Halada”) is morphologically very close to C. florisomne except for the comb of long yellowish bristles along the apical margin of sternum 5, which covers only the central half of the sternal width rather than the entire sternal width as in C. florisomne . This male is tentatively regarded as an aberrant specimen of C. florisomne until further material from northwestern Turkey is available.