Bombus ashtoni

(Cresson, 1864)

Ashton's cuckoo bumble bee

ashtoni is a cuckoo (subgenus Psithyrus) to North America. Unlike social bumble bees, this does not produce or construct its own nests. Instead, females infiltrate established colonies of other Bombus species and exploit the workers to rear their own offspring. This parasitic lifestyle has been documented specifically with hosts including Bombus affinis, Bombus terricola, and Bombus fervidus. The species is subject to the same concerns affecting its host species, particularly the endangered rusty patched bumble bee (B. affinis).

Bombus (Psithyrus) ashtoni by the Smithsonian. Used under a CC0 license.

Pronunciation

How to pronounce Bombus ashtoni: /ˈbɒm.bəs ˈæʃ.tə.naɪ/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

As a member of the subgenus Psithyrus, B. ashtoni can be distinguished from non-parasitic by the absence of pollen-carrying () on the hind legs of females. Cuckoo also lack the dense body hair typical of social species, appearing relatively sleek. Specific identification to species level requires examination of coloration patterns and microscopic features; B. ashtoni exhibits particular combinations of black, , and sometimes reddish or markings that distinguish it from other Psithyrus species in its range.

Images

Distribution

North America. The has been recorded in the United States and Canada, with its distribution corresponding to that of its species. Specific state and provincial records align with the ranges of affinis (now largely restricted to the upper Midwest), Bombus terricola (northern and montane regions), and Bombus fervidus (transcontinental in northern areas).

Host Associations

Bombus affinis - Primary ; B. affinis is federally endangered in the United States
Bombus terricola - Known
Bombus fervidus - Known

Life Cycle

Females emerge from in spring and seek out established colonies. The cuckoo female kills or subdues the host and assumes reproductive control of the colony. She lays that are tended by host , which also provision the developing cuckoo . Male and female offspring are produced; mated females enter to overwinter and repeat the cycle the following year. No worker is produced—this relies entirely on host workers for colony maintenance.

Behavior

Females engage in aggressive usurpation of colonies, often killing the resident upon entry. This exhibits the cuckoo : females possess a thick, heavily sclerotized and mandibular structures adapted for combat with host queens. Males areas near host colonies seeking mates. The species does not forage for pollen or nectar to provision offspring, though may visit flowers for their own nutritional needs.

Ecological Role

As an obligate , B. ashtoni functions as a regulator of its . Its persistence is entirely dependent on healthy host populations. The species may contribute to local extinction of host colonies, though at natural population levels this is balanced by host and . The decline of host species, particularly B. affinis, threatens the long-term viability of B. ashtoni populations.

Human Relevance

The has no direct economic value, but its status is linked to that of its , including the agriculturally important rusty patched . B. ashtoni serves as an indicator of bumble bee health and intact ecological interactions. Its presence in an area confirms functioning of host species. The species is of interest to conservation biologists studying decline and parasitic .

Similar Taxa

Bombus (Psithyrus) citrinusAnother cuckoo with overlapping eastern range; distinguished by color pattern and associations
Bombus (Psithyrus) insularisWidespread cuckoo with broader range; B. ashtoni more specialized to particular host species
Bombus (Psithyrus) fernaldaeSimilar size and coloration; requires careful examination of abdominal pattern and markings for separation

More Details

Conservation concern

The status of B. ashtoni is directly tied to that of its . The dramatic decline of affinis, which has lost approximately 90% of its historic range and was listed as endangered in 2017, poses a significant threat to B. ashtoni in the upper Midwest. The species may qualify for attention under the logic of host- coextinction risk, though it receives no independent legal protection.