Chelostomoides

Taxonomy

Family: Megachilidae
Subfamily: Megachilinae
Tribe: Megachilini
Genus: Chelostomoides Robertson, 1901
Common name: none

Overview

Chelostomoides are narrow bees, often with black integument and contrasting pale apical bands on the terga (Michener 2007). They range in body length from 7–17 mm (Michener 2007). This group was elevated from a subgenus of Megachile to genus status by Gonzalez et al. (2019).

Diagnostic characteristics

(modified from Mitchell 1937b; Michener 2007; Gonzalez 2008)

Female F1 is shorter than the pedicel.
Female mandible is highly variable but lacks a cutting edge.
Female S6 with dense, uniform hairs.
Female tarsal claws without basal teeth.
Female terga basal grooves are covered in pale hairs.
Male mandible is three-toothed.

May be confused with

Chelostomoides may be confused with bees within Megachile (Chelostomoda) due to having similar size, body shape, and postgradular grooves (Michener 2007). Chelostomoides, however, have hairs in the postgradular grooves, lack cutting edges on their mandibles, and the females of some species have a highly modified clypeus (Michener 2007). These bees, while similar morphologically, have very different distributions: Chelostomoides is native to the Americas and Chelostomoda to Australia and Asia.

Host associations

Chelostomoides has been observed visiting flowers within the plant families of Aquifoliaceae, Asteraceae, Boraginaceae, Cactaceae, Campanulaceae, Clethraceae, Eriocaulaceae, Fabaceae, Haemodoraceae, Hypericaceae, Lamiaceae, Malvaceae, Onagraceae, Orobanchaceae, Papaveraceae, Plantaginaceae, Polygalaceae, Polygonaceae, Verbenaceae, and Zygophyllaceae (Mitchell 1937b; Deyrup et al. 2002).

Nesting behavior

Chelostomoides nest in pre-existing cavities; they have been recorded nesting in abandoned beetle burrows, in cavities in wood, twigs, and stems, and in nail holes and holes in walls (Armbrust 2004; Michener 2007). Most of these bees collect plant resins to build their nests, although M. discorhina produces a secretion that it uses as an adhesive instead of using resins (Armbrust 2004). Chelostomoides use a variety of other materials in nest construction, including sand, pebbles, chewed leaves, and small pieces of wood (Armbrust 2004; Michener 2007). The composition of the nest plugs in particular can vary significantly, even between members of the same species (Armbrust 2004; Michener 2007). These plugs create a barrier between the opening of the cavity and the nest cells and can consist of a single layer of resin or a series of several layers of different materials (Armbrust 2004).

Diversity

Chelostomoides contains thirty-three species (Michener 2007; Raw 2007; Gonzalez et al. 2019).

Known invasives

There are no known invasives in the U.S. However, Chelostomoides otomita, which is native to the U.S., has become established in the Canary Islands, a Spanish archipelago off the western coast of Africa (Strudwick and Jacobi 2018).

Distribution

Chelostomoides are native to North America and northern South America. In North America, they have a transcontinental range with the northern boundary extending from British Columbia, Canada to New York (Giles and Ascher 2006; Michener 2007). They are widespread south of this boundary, including throughout the Caribbean Islands, Mexico, and Central America to South America, where they have been recorded in Colombia and Peru (Michener 2007).

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