Overview

Distribution

National Distribution

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (Unknown) The recent range was large, well over a million square miles, but the current range might or might not be much smaller. The Discover Life Website map as of March 2010 indicated a historic range from New Hampshire to Wisconsin, South Dakota, and North Dakota (questionable, beyond likely range of host, and reference not completed) south to Arkansas, where it is the only native bumblebee not encountered by Warriner (2011), and northern Florida. However, Smith et al. (2012) do report it from two counties in Mississippi from 1999 to 2001. It also occurs apparently disjunctly in New Mexico and Arizona as well as Central America from southern Mexico to at least Honduras and Guatemala (see also Williams 2008 [1998]). Recently discovered in central Nebraska (Golig and Ellis, 2006). This is a relatively southern bumblebee and may not reach Canada.

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Ecology

Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Associations

Flowering Plants Visited by Psithyrus variabilis in Illinois

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: Unknown

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Global Abundance

Unknown

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General Ecology

This is an obligate nest parasite (usurper) of other bumble bees. Plath (1922) and Williams (2008b) report what is now Bombus (Thoracobombus) pensylvanicus as the host (victim). Its occurrence in new Mexico and Arizona indicates subspecies or species P. p. sonorus is used. No other host species has been reported, but records of this species in southern Mexico to Honduras indicate a second host since sonorus apparently does not go that far south.

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Bombus variabilis

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 5
Species With Barcodes: 1
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Conservation

Conservation Status

National NatureServe Conservation Status

Canada

Rounded National Status Rank: NU - Unrankable

United States

Rounded National Status Rank: NU - Unrankable

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NatureServe Conservation Status

Rounded Global Status Rank: GU - Unrankable

Reasons: Both subspecies of the only known host (victim) for this obligate nest parasite are declining, but not as rapidly as some other bumblebees, nevertheless this obligate nest parasite has become undetectable in some places wher the host is persisting (Warriner, 2011). B. (P.) variabilis is not suspected to be close to extinction now, although that possibility (or at least exrtirpation in the US) cannot be ruled out, so the only defensible rank is GU to match the known host species, and that is also the rank from Rank Calculator v3.1 August 2012. Grixti et al. (2009) directly document a decline of B. (P.) variabilis. Colla and Packer (2008) documented declines of two closely related species, but this one apparently did not occur in their study area in Ontario. Another confounding issue is that occurrence in southern Mexico, Guatemala, and Honduras imply another host species. Status there is unknown and the taxonomy is questionably resolved at present.

Intrinsic Vulnerability: Highly vulnerable

Comments: Obligate nest parasite on two closely related declining taxa.

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Global Short Term Trend: Decline of 10 to >90%

Comments: Severity of decline in North America is uncertain, but should be at least as severe as for the obligate host. Status in Central America is unknown.

Global Long Term Trend: Decline of 10-90%

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Threats

Degree of Threat: Very high - high

Comments: The only known threat is the significant widespread decline of the only known host species, Bombus pensylvanicus, including subspecies or species sonorus. See ranking account for that species. As with other Psithyrus this one could decline more rapidly than its host if the host becomes scarce enough.

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Management

Global Protection: Unknown whether any occurrences are appropriately protected and managed

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Wikipedia

Bombus variabilis

Bombus variabilis is a species of cuckoo bumblebee.

References[edit]

  1. ^ "Bombus variabilis (Cresson, 1872)". Biolib.cz. Retrieved 3 July 2012. 


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Names and Taxonomy

Taxonomy

Comments: Subgenus: Psithyrus

Williams (2008[1998]) considers the taxa B. (Ps.) sololensis, B. (Ps.) intrudens, B. (Ps.) mysticus, and B. (Ps.) guatemalensis named from Mexico and Central America as conspecific. This circumscription is followed here, and could affect the global rank. If this circumscription is correct, the oldest name for the species would be B. intrudens. As Williams points out that name has not been appplied for this species in any modern literature and therefore we'll continue to use the long-standing name B. variabilis in this database. It might be a good candidate for suppression by ICZN in the interest of stability.

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