Chelostoma

Taxonomy

Family: Megachilidae
Subfamily: Megachilinae
Tribe: Osmiini
Genus: Chelostoma Latreille, 1809
Subgenera: Chelostoma, Eochelostoma, Foveosmia, Gyrodromella, Prochelostoma
Common name: none

Overview

Chelostoma are small to moderately sized bees with slender, elongated bodies, and overall black coloration (Michener 2007). Species native to North America range in body length from 3.4–9 mm, but some Eurasian species reach a length of 14 mm (Michener 2007).

Diversity

Chelostoma contains 54 described species in 5 subgenera worldwide (Michener) and at least 7 undescribed species (Müller 2018b). 11 species within 3 subgenera: Foveosmia, Prochelostoma, Gyrodromella occur in the U.S. and Canada (Michener 2007).

Diagnostic characteristics

(modified from Michener 2007)

May be confused with

Chelostoma may resemble Hoplitis because of the elongated appearance. Chelostoma tends to have a longer scutum than Hoplitis. In addition, the labrums of Chelostoma females have few and inconspicuous erect setae, and S6 of the male is usually exposed (Michener 2007).

Known invasives

Chelostoma campanularum is native to Europe and the Near East and was introduced to the U.S. in the 1960-70’s. It has a limited range, including upstate New York and Connecticut, and may be common in southern Ontario, Canada metropolitan areas (Buck et al. 2005).

Chelostoma rapunculi is native to Europe and the Near East and was probably introduced around the same time as C. campanularum. Chelostoma rapunculi is adventive to most of the same areas as C. campanularum, occurring in upstate New York and southern Ontario, but may not be as common (Buck et al. 2005).

Host associations

Chelostoma, apart from 2 species, consists of species that florally specialize at either the family or genus level (Sedivy et al. 2008). The families that Chelostoma specialize on are diverse and include Amaryllidaceae (1 species), Campanulaceae (13 species), Hydrophyllaceae (6 species), Ranunculaceae (4 species), Dipsacaceae (2 species), Asteraceae (2 species), Brassicaceae (2 species), Asparagaceae (1 species), Hydrangeaceae (1 species), Theaceae (1 species). Sedivy et al. (2008) provides host associations for 35 Chelostoma species.

Nesting behavior

Chelostoma are solitary bees that nest in preexisting cavities such as dead wood, hollow stems, and holes made by wood-boring beetles. Nests are not lined, but partitions and nest plug are made with a mixture of mud or sand mixed with nectar and saliva (Michener 2007). Some species also include small particulates, such as tiny pebbles, in their cell partitions and nest plug (Müller 2018).

Distribution

Chelostoma have a Holarctic distribution, except for China and Japan. In North America, eight of the native species occur in California with a few of these species occurring north to Washington. One species, C. minutum, is distributed in the Intermountain West in Utah and Idaho. The only native species known to occur in central and eastern North America is C. philadelphi. Two additional species of adventive Chelostoma, C. (Foveosmia) campanularum and C. (Gyrodromella) rapunculi, occur in the Northeast (Michener 2007).

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<p><em>Chelostoma californicum </em>female abdomen, photo: C. Ritner</p>
Chelostoma californicum female abdomen, photo: C. Ritner
<p><em>Chelostoma californicum </em>female lateral habitus, photo: C. Ritner</p>
Chelostoma californicum female lateral habitus, photo: C. Ritner
<p><em>Chelostoma californicum </em>female abdomen, photo: T. Brady</p>
Chelostoma californicum female abdomen, photo: T. Brady
<p><em>Chelostoma campanularum </em>male face, photo: S. Adams</p>
Chelostoma campanularum male face, photo: S. Adams
<p><em>Chelostoma campanularum </em>male lateral habitus, photo: S. Adams</p>
Chelostoma campanularum male lateral habitus, photo: S. Adams
<p><em>Chelostoma campanularum </em>male dorsal habitus, photo: S. Adams</p>
Chelostoma campanularum male dorsal habitus, photo: S. Adams
<p><em>Chelostoma campanularum </em>male apical terga, photo: S. Adams</p>
Chelostoma campanularum male apical terga, photo: S. Adams
<p><em>Chelostoma phaceliae</em> female mesopleuron longer than scutum, photo: C. Ritner</p>
Chelostoma phaceliae female mesopleuron longer than scutum, photo: C. Ritner