SPECIES: Scientific [common] Bombus suckleyi [Suckley’s cuckoo bumble ] Forest: Salmon-Challis National Forest Forest Reviewer: Mary Friberg Date of Review: 12/28/2017 Forest concurrence (or Yes recommendation if new) for inclusion of species on list of potential SCC: (Enter Yes or No)

FOREST REVIEW RESULTS:

1. The Forest concurs or recommends the species for inclusion on the list of potential SCC: Yes__X_ No___

2. Rationale for not concurring is based on (check all that apply): Species is not native to the plan area ______Species is not known to occur in the plan area ______Species persistence in the plan area is not of substantial concern ______

FOREST REVIEW INFORMATION:

1. Is the Species Native to the Plan Area? Yes_X__ No___

If no, provide explanation and stop assessment.

2. Is the Species Known to Occur within the Planning Area? Yes_X__ No___

If no, stop assessment. Table 1. All Known Occurrences, Years, and Frequency within the Planning Area Year Number of Location of Observations (USFS Source of Information Observed Individuals District, Town, River, Road Intersection, HUC etc.) 1960 10 Gibbonsville, ID (Lemhi County) The Global Biodiversity Information Facility Occurrence Download (October 2017) 1957 1 North Fork, ID (Lemhi County) The Global Biodiversity Information Facility Occurrence Download (October 2017)

a. Are all Species Occurrences Only Accidental or Transient?

Yes___ No_X__

If yes, document source for determination and stop assessment.

b. For species with known occurrences on the Forest since 1990, based on the number of observations and/or year of last observation, can the species be presumed to be established or becoming established in the plan area?

Yes___ No___

If no, provide explanation and stop assessment

N/A – no occurrences have been documented since 1990

c. For species with known occurrences on the Forest predating 1990, does the weight of evidence suggest the species still occurs in the plan area?

Yes_X__ No___

Provide explanation for determination

Suckley’s cuckoo bumble bee is widely distributed on and around the Forest (see Map 1). The host species (the Western bumble bee) is still extant on the Forest (see Criterion 1), presumably at low densities. Parasitic species typically exist at lower abundances than their host species (see Criterion 4), and due to their life history are likely to be underrepresented in surveys (see Criterion 1), so it is possible that Suckley’s cuckoo bumble bee exists in low numbers on the Forest.

If determination is no, stop assessment

d. Map 1, Suckley’s cuckoo bumble bee range in Idaho (IDFG 2017a)

IDFG (Idaho Department of Fish and Game). 2017. Suckley’s bumble bee (Bombus suckleyi). Internet website: https://idfg.idaho.gov/species/taxa/1475541. Accessed on October 23, 2017. e. Map 2, Suckley’s bumble bee occurrences on the Salmon-Challis National Forest (Idaho Fish and Wildlife Information System [January

2017]) 3. Is There Substantial Concern for the Species’ Capability to persist Over the Long-term in the Plan Area Based on Best Available Scientific Information?

Table 2. Status summary based on existing conservation assessments

Entity Status/Rank (include definition if Other)

NatureServe G1G3- Critically imperiled/Vulnerable (At very high risk of extinction due to extreme rarity (often 5 or fewer populations), very Global Rank steep declines, or other factors/At moderate risk of extinction due to a restricted range, relatively few populations (often 80 or fewer), recent and widespread declines, or other factors) NatureServe S2- Imperiled (At high risk of extinction due to a very restricted range, very few populations (often 20 or fewer), steep declines, State Rank or other factors) State List IDAPA- Status SGCN- Tier 1 (Highest priority for the SWAP; represents species with the most critical conservation needs, i.e., an early-warning list of taxa that may be heading toward extirpation) USDA Forest Not Region 1 Sensitive Service Not Region 4 Sensitive

USDI FWS No records found Other Not BLM Type 2 Not ranked by the Xerces Society

Table 3. Status summary based on best available scientific information.

Species (Scientific and Common Name): Bombus suckleyi [Suckley’s cuckoo bumble bee]

Criteria Rank Rationale Literature Citations 1 A1 Suckley’s cuckoo bumble bee is known on the Forest from two historic The Global Biodiversity Information Distribution on occurrence records in the North Fork Ranger District (see Table 1). The Facility Occurrence Download Salmon-Challis most recent occurrence record is from 1960 (see Table 1). However, its (October 2017). National Forest host (the Western bumble bee) was sighted in 2017 near North Fork (see PSCC for Western bumble bee), which is also the location of one of the Thorp, R. W., D. S. Horning, and L. L. two historic records of Suckley’s cuckoo bumble bee. It is possible that Dunning. 1983. Bumble and host populations have remained stable in areas with historic records of cuckoo bumble bees of Suckley’s cuckoo bumble bee (see Criterion 6). In addition, cuckoo (: ). Bulletin of bumble bees do not produce workers, so adults would only be the California Survey: Vol. encountered above ground during host searching and mating flights 23. making surveys for Suckley’s cuckoo bumble bee challenging (Thorp, Horning, and Dunning 1983). Therefore, Suckley’s cuckoo bumble bee could still be extant on the Forest despite the lack of current occurrence records.

Due to presumed declines in abundance of its host (see PSCC for Western bumble bee), the narrow range of recorded historical occurrences, and low dispersal ability (see Criterion 3), we predict that habitat is widely distributed but isolated and scarce across the Forest, increasing the potential of local extirpations (Rank A1). Confidence is low due to lack of recent occurrence data for Suckley’s cuckoo bumble bee and uncertainty of the current distribution and abundance of the Western bumble bee on the Forest.

Confidence in Rank: High, Medium, or Low 2 C Suckley’s cuckoo bumble bee distribution is centered in western North Hatfield, R., Jepsen, S., Thorp, R., Distribution in America (Hatfield et al. 2015). Its historic range includes the Mountain Richardson, L. & Colla, S. surrounding West from northern California to Alaska, and extends east to New 2015. Bombus suckleyi. The IUCN geographic area Mexico, Colorado, and Dakotas (Hatfield et al. 2015). There is also a Red List of Threatened Species historic isolated population in the northeastern United States (Hatfield et 2015: e.T44937699A46440241. al. 2015). Current surveys indicate that Suckley’s cuckoo bumble bee is extant from Northern California to New Mexico, extending north to IDFG (Idaho Department of Fish portions of southern Alberta and British Columbia (Hatfield et al. 2015). and Game). 2017b. Idaho State Few occurrence records exist for Suckley’s cuckoo bumble bee in Idaho Wildlife Action Plan, 2015. Boise, (IDFG 2017b), but surveys conducted between 2002-2012 documented ID. occurrences in northern Idaho, Montana, and northwest Wyoming near the borders of Idaho and Montana (Hatfield et al. 2015). Based on surveys and historical records, the current range of Suckley’s cuckoo bumble bee (post-2002) encompasses only 43% of its historic range (Hatfield et al. 2015).

Recent surveys indicate Suckley’s cuckoo bee has a wide distribution outside the Salmon-Challis National Forest (Rank C), although it is experiencing range contraction.

Confidence in Rank: High, Medium, or Low 3 B Although nonparasitic bumble bee queens can disperse up to several Erler, S., and H. M. G. Lattorff. Dispersal kilometers while searching for nest sites, genetic studies of Bombus 2010. The degree of parasitism of Capability vestalis indicate that parasitic bumble bee queens do not disperse long the () distances (Erler and Lattorff 2010). Therefore, Suckley’s cuckoo bumble by cuckoo (Bombus bee probably only disperses through suitable habitat (Rank B). () vestalis). Insectes Confidence in this rank is low due to the lack of species-specific data on Sociaux: Vol. 57: No. 4. the specie’s dispersal capability.

Species (Scientific and Common Name): Bombus suckleyi [Suckley’s cuckoo bumble bee]

Criteria Rank Rationale Literature Citations Confidence in Rank: High, Medium, or Low

4 A There is no information for abundance or population density of Suckley’s Erler, S., and H. M. G. Lattorff. Abundance on the cuckoo bumble bee on the Forest (IDFG 2017b). Based on available 2010. The degree of parasitism of Salmon-Challis information, its host is probably uncommon on the Forest (see PSCC for the bumblebee (Bombus terrestris) National Forest Western bumble bee). Cuckoo bumble bees are typically more rare than by cuckoo bumblebees (Bombus their host species (Erler and Lattorff 2010). Rangewide, Suckley’s cuckoo (Psithyrus) vestalis). Insectes bumble bee has decreased in relative abundance by about 10% when Sociaux: Vol. 57: No. 4. comparing survey data from before and after 2002, and has been experiencing significant decreases in relative abundance in the past 50 Hatfield, R., Jepsen, S., Thorp, R., years (Hatfield et al. 2015). Richardson, L. & Colla, S. 2015. Bombus suckleyi. The IUCN Based on rangewide relative abundance trends and the estimated Red List of Threatened Species abundance of its host on the Forest, Suckley’s cuckoo bumble bee is 2015: e.T44937699A46440241. probably rare on the Forest (Rank A). Confidence is low due to lack of Forest-specific data on either Suckley’s cuckoo bumble bee or the Western bumble bee. IDFG (Idaho Department of Fish and Game). 2017b. Idaho State Confidence in Rank: High, Medium, or Low Wildlife Action Plan, 2015. Boise, ID. 5 A There is no Forest-specific information on population trends of Suckley’s Dolan, A. C., C. M. Delphia, K. M. Population Trend cuckoo bumble bee. Across its range, it is estimated that Suckley’s O’Neill, and M. A. Ivie. 2017. on the Salmon- cuckoo bumble bee populations have declined by 77% when comparing Bumble bees (Hymenoptera: Challis National historic (pre-2002) and current occurrence data (Hatfield et al. 2015). If Apidae) of Montana. Annals of the Forest its current trajectory continues, relative abundance of Suckley’s cuckoo Entomological Society of America: bumble bee is predicted to drop to zero within the next 10 years Vol. 110: No. 2. (Hatfield et al. 2015). Patterns of decline in Suckley’s cuckoo bumble bee follow declines observed in its host (see PSCC for Western bumble bee). Hatfield, R., Jepsen, S., Thorp, R., Analysis of historic occurrence records and current (2015) surveys in Richardson, L. & Colla, S. Montana provide evidence that Suckley’s cuckoo bumble bee is also in 2015. Bombus suckleyi. The IUCN decline in this region despite the fact that the most severe declines of its Red List of Threatened Species host are reported further west (Dolan et al. 2017). 2015: e.T44937699A46440241.

Based on rangewide and nearby population trends, Suckley’s cuckoo bumble bee populations are likely to be in decline on the Forest (Rank A). Confidence is medium due to lack of Forest-specific data.

Confidence in Rank: High, Medium, or Low 6 A With regard to floral resources, above ground adults, which are active Montana Field Guide. Suckley Habitat Trend on from roughly May through October, have also been observed visiting a cuckoo bumble bee: Bombus the Salmon-Challis variety of composites, , and Penstemon, presumably to collect suckleyi. Accessed October 2017. nectar to fuel flight activity (Thorp et al. 1983). Specific vegetation types in which Suckley’s cuckoo bumble bee occurs have not been documented Thorp, R. W., D. S. Horning, and L. L. on the Forest, but in other regions Suckley’s cuckoo bumble bee has Dunning. 1983. Bumble bees and been observed in a variety of vegetation types, including grassland, shrub cuckoo bumble bees of California steppe, and montane and subalpine meadows (Montana Field Guide (Hymenoptera: Apidae). Bulletin of 2017). In general, the host of Suckley’s cuckoo bumble bee relies on the the California Insect Survey: Vol. presence of abundant and stable floral resources, overwintering sites, 23. and underground cavities such as abandoned rodent burrows (see USFS 2017). For further description see USFS (2017). In summary, information USFS (United States Department of on trends in floral resources are scarce, but broad habitat specificity, Agriculture, Forest Service). 2017. abundance of potentially suitable habitat, and trends in their quantity Bombus occidentalis (Western and quality suggest Suckley’s cuckoo bumble bee foraging habitat on the bumble bee) assessment for Forest is likely stable. potential species of conservation concern. On file, Salmon-Challis However, the most important habitat requirement of Suckley’s cuckoo National Forest, Salmon, ID. bumble bee is the presence of its host, the Western bumble bee. Abundance and populations of the Western bumble bee appear to be declining on the Forest (USFS 2017), thus a rank of A. Confidence is low due the lack of Forest-specific information on abundance and population trends of the Western bumble bee.

Confidence in Rank: High, Medium, or Low 7 B Since suitable habitat for Suckley’s cuckoo bumble bee is determined by Vulnerability of the presence of its host, habitat for Suckley’s cuckoo bee shares the IDFG (Idaho Department of Fish Habitats on the same vulnerabilities as habitat for the Western bumble bee (IDFG 2017). and Game). 2017b. Idaho State Salmon-Challis For details see the Western bumble bee vulnerability assessment (USFS Wildlife Action Plan, 2015. Boise, National Forest 2017). In summary, declines in Western bumble bee populations appear ID. to be tied more to its life history and demographics than habitat loss. However, they may be moderately vulnerable to modification of habitat USFS (United States Department of

Species (Scientific and Common Name): Bombus suckleyi [Suckley’s cuckoo bumble bee]

Criteria Rank Rationale Literature Citations by spread and control of invasive weeds, global changes in climate, and Agriculture, Forest Service). 2017. unrestricted grazing. The Western bumble bee has an annual life cycle, Bombus occidentalis (Western and variability in reproductive success is high. Additionally, genetic bumble bee) assessment for factors, competition with honey bees, and parasite/pathogen potential species of conservation relationships all contribute to the high vulnerability of the species (Rank concern. On file, Salmon-Challis A). Confidence in this rank is medium because the actual reproductive National Forest, Salmon, ID. capacity of the Western bumble bee is unknown, and there is no Forest- specific data on reproduction and disease rates. Since Suckley’s cuckoo bumble bee relies on the Western bumble bee as a host, its habitat is also expected to undergo substantial modification (Rank A). Confidence is also medium.

Confidence in Rank: High, Medium, or Low 8 A Cuckoo bumble bee queens emerge later than queens of their host Erler, S., and H. M. G. Lattorff. Life History and species (Goulson 2003). They reproduce by usurping established host 2010. The degree of parasitism of Demographics nests (Goulson 2003). Host queens are either killed or subdued, and the bumblebee (Bombus terrestris) worker bumble bees are conscripted to rear cuckoo bumble bee offspring by cuckoo bumblebees (Bombus (Goulson 2003). Unlike their hosts, cuckoo bumble bees only produce (Psithyrus) vestalis). Insectes reproductive offspring (Goulson 2003). Sociaux: Vol. 57: No. 4.

Although the Suckley’s cuckoo bumble bee has been found in nests of Fisher, R. M. 1988. Observations on several bumble bee species, successful reproduction has only been the behaviours of three European documented in nests of the Western bumble bee (Thorp, Horning, and cuckoo bumble bee species. Dunning 1983). On the Forest, Suckley’s cuckoo bumble bee most likely Insected Sociaux: Vol. 35: No. 4. relies on populations of the Western bumble bee for reproduction. This level of host specialization, combined with host species decline, makes Goulson, D. E. 2003. Bumblebees: Suckley’s cuckoo bee highly vulnerable to extirpation. Threats to the Their Behavior and Ecology. Oxford Western bumble bee include parasites and pathogens, and high variation University Press. in reproductive success (see PSCC for Western bumble bee). Hatfield, R., Jepsen, S., Thorp, R., No species-specific life history or demography data exists for Suckley’s Richardson, L. & Colla, S. cuckoo bumble bee, but some inferences can be made using information 2015. Bombus suckleyi. The IUCN from the life histories of other cuckoo bumble bee species. Cuckoo Red List of Threatened Species bumble bee reproductive success depends on the ability of queens to 2015: e.T44937699A46440241. usurp a host colony and subsequent reproductive capacity. Usurpation success of a European cuckoo bumble bee appears to be very high Lepais et al. 2010. Estimation of (100%) when host colonies are new/small, and decreases as host colony bumblebee queen dispersal age and size increase (Sramkova and Ayasse 2009). Based on anecdotal distances using sibship observations, within the same nest reproduction of three species of reconstruction method. Molecular European cuckoo bumble bees appears to be lower than reproduction of Ecology: Vol. 19. their host species (Fisher 1988). The Western bumble bee appears to have highly variable, and often low, reproductive success (see PSCC for Sramkova, A., and M. Ayasse. 2009. Western bumble bee), so reproduction of Suckley’s cuckoo bumble bee is Chemical ecology involved in probably also low. invasion success of the cuckoo bumblebee Psithyrus vestalis and in Additional direct threats to Suckley’s cuckoo bumble bee include disease survival of workers of its host and low genetic diversity. Suckley’s cuckoo bee can become infected with Bombus terrestris. Chemoecology: the microsporidian , which is prevalent in populations of Vol. 19. the Western bumble bee (see PSCC for Western bumble bee) (Hatfield et al. 2015). Bumble bees are haplodiploid (males only have one set of Thorp, R. W., D. S. Horning, and L. L. chromosomes), and sex is determined by heterozygosity at a single locus Dunning. 1983. Bumble bees and (Lepais et al. 2010). Decreased genetic variation, resulting from cuckoo bumble bees of California population declines, increases the risk of production of homozygous, (Hymenoptera: Apidae). Bulletin of sterile gynes. Genetic variation in the cuckoo bee Bombus vestalis was the California Insect Survey: Vol. significantly lower than in its host, probably due in part to lower dispersal 23. ranges (see Criterion 3) (Erler and Lattorff 2010), which suggests that Suckley’s cuckoo bee probably has low levels of heterozygosity.

Thus, low levels of reproduction and reliance on a declining host species would make recovery of Suckley’s cuckoo bumble bee populations from disturbance events very difficult (Rank A). Decreased genetic variation and pathogen infection are also risk factors for this species. Confidence in this rank is low due to the lack of species-specific data on reproduction, as well as the exact status of the Western bumble bee on the Forest.

Confidence in Rank: High, Medium, or Low Summary and recommendations: Date: 12/28/2017

Suckley’s cuckoo bumble bee (Bombus suckleyi) is widely distributed across western North America, but it has experienced dramatic declines in the past 50 years that mirror declines in its primary host species, the Western bumble bee. Global and statewide conservation assessments indicate substantial concern for this species. It is known on the Forest from two historic occurrence records, although based on current distribution of its host

Species (Scientific and Common Name): Bombus suckleyi [Suckley’s cuckoo bumble bee]

Criteria Rank Rationale Literature Citations species it could still be present on the Forest. Based on rangewide patterns of both Suckley’s cuckoo bumble bee and its host, it is probably rare and in decline on the Forest. The main habitat requirement of Suckley’s cuckoo bumble bee is the presence of the Western bumble bee. Although potential suitable habitat for the Western bumble bee appears to be stable on the Forest, populations are probably in decline due to life history and demographic risk factors. Habitat for Suckley’s cuckoo bumble bee is therefore in decline on the Forest. Indirectly, the species is vulnerable to habitat degradation from unrestricted grazing, noxious weed invasion and suppression, and global changes in climate. Poor dispersal ability, coupled with declining host abundance, are likely to threaten persistence of Suckley’s cuckoo bumble bee populations. Major risk factors for Suckley’s cuckoo bumble bee include its presumed low reproduction rates and reliance on a declining host species population for reproduction. Loss of genetic variation and disease may further affect Suckley’s cuckoo bumble bee.

In summary, Suckley’s cuckoo bumble bee appears to be rare and declining on the Forest. It is at risk of extirpation primarily due to its poor dispersal abilities and reliance on an uncommon and declining host species. Thus, there is substantial concern for the capability of the Suckley’s cuckoo bumble bee to persist over the long-term on the Salmon-Challis and it is recommended as a potential SCC on the Forest.

Evaluator(s): Rei Scampavia and Mary Friberg