Franklin's bumblebee (Bombus franklini) is known to be one of the most narrowly distributed bumblebee species, making it a critically endangered bee of the western United States. It is known only from a 190-by-70-mile (310 by 110 km) area in southern Oregon and northern California, between the Coast and Sierra-Cascade mountain ranges. It was last seen in 2006. Franklin's bumblebee is known to collect and nectar pollen from several wildflowers, such as lupine, California poppy, and horsemint, which causes it to be classified as a generalist forager. Neonicotinoids, highly toxic to bees, were used starting in the early 1990s in North America, and were commonly used as systematic insecticides in many regions of the United States for crop and turf pest control. Other pesticides include organophosphates, carbamates, pyrethroids, and spinosad. Bumblebees are susceptible to habitat loss due to limited flight range, long colony cycle, and specific needs for food and nesting. Bumblebees have a special technique in foraging that makes them exclusive pollinators of certain plants. They engage in “buzz pollination” by which they vibrate the flowers with sound to loosen and collect the pollen. Some examples of plants on which they use this method include tomatoes and blueberries. This method of pollination allows them to pollinate crops, and greatly affects the U.S. economy. Bees pollinate crops valued at more than $15 billion a year. These crops include apples, berries, cantaloupes, cucumbers, alfalfa, and almonds.
Franklin's bumblebee is accepted as a distinctive species separate from other species of Bombus and is hard to distinguish because it is very rare, but also because many species of Bombus, including B. franklini, are cryptic, therefore misleading, and almost impossible to identify. However, a member of B. franklini can be distinguished from other bumblebees by its distinctive pattern of yellow on the anterior top of the thorax that extends behind the wing bases to the top of its head. They have a solid black abdomen. Its yellow thorax has black, U-shaped design. Females have black hair on their faces and the vertices, while other bumblebees have yellow. Males of this species are similar except their malar spaces are long and wide. The hair on their faces is also yellow, and tergum 6 has some pale hairs laterally.
The queen and workers of this species can be identified with a round face with an area between the bottom of the compound eye and base of mandible. They also have pitch black hair with some light hairs mixed above and below their antennal bases.
Of any North American bumblebee, Franklin's bumblebee has the smallest range. Few, if any, sightings of this bumblebee have been made in the last decade. Studies and records say this species is already extinct, but records from 2006 indicate an individual sighted in Oregon. Until more concrete evidence is shown, this species was assigned a conservation status rank of G1, which is critically imperiled. Furthermore, the population has decreased drastically since 1998. A reason for the lack of major conservation efforts is the rarity of pesticide toxicity tests on wild bee species. These tests may indicate long-term effects of pesticides on bumblebee colonies' foraging and the effects on adult bees that fed on pesticide-exposed pollen during their larval stage.
- C. M. Pollock & C. Hilton-Taylor (2008). "Bombus franklini". IUCN Red List of Threatened Species. Version 2012.1. International Union for Conservation of Nature. Retrieved September 12, 2012.
- Williams, Paul H.; et al (2012). "Unveiling cryptic species of the bumblebee subgenus Bombus s. str. worldwide with COI barcodes (Hymenoptera: Apidae)". Systematics and Biodiversity 10 (1): 21–56. doi:10.1080/14772000.2012.664574.
- Jeff Barnard (24 June 2010). "Group seeks endangered listing for Franklin's bumblebee". USA Today. Retrieved 12 September 2012.
- Colla, Sheila; Laurence Packer (2008). "Evidence for decline in eastern North American bumblebees (Hymenoptera: Apidae), with special focus on Bombus affinis Cresson". Biodiversity and Conservation. doi:10.1007/s10531-008-9340-5.
- Morandin, Lora, A; et al (2005). "Lethal and sub‐lethal effects of spinosad on bumble bees (Bombus impatiens Cresson)". Pest Management Science 61 (7): 619–626. doi:10.1002/ps.1058.
- Grixti, J.C.; L.T. Wong, S.A. Cameron, C. Favret (2008). "Decline of bumble bees (Bombus) in the North American Midwest". Biological Conversation. doi:10.1016/j.biocon.2008.09.027.
- "Franklin's bumblebee (Bombus franklini) species profile". Environmental Conservation Online System. United States Fish and Wildlife Service.
- Bumble bees: Franklin's bumble bee (Bombus franklini) at Xerces Society website