Rusty patched bumble bees (Bombus affinis) are native to the Nearctic region. Their historic range encompassed 186 counties in 31 U.S. states and 2 Canadian provinces across 15 ecoregions. In Canada, their historic range extended as far as southwest Ontario, continuing east along the southern edge of Ontario and Quebec, likely as far east as Montréal, Quebec. In the continental United States, rusty patched bumble bees inhabited areas as far west as Minnesota, eastern Iowa, and the junction of North and South Dakota, near their shared border with Minnesota. Their range extended east, through the Great Lakes Region and New England, as far as central Maine. The historic range of rusty patched bumble bees extended southward from Maine, along the Atlantic Coast. From Maryland, their range extended west through West Virginia, Ohio, Indiana, and the northern half of Illinois. Their distribution also extended south of Maryland and West Virginia, but only to areas in and around the Appalachian Mountain range. This southernmost portion of their historic range included central and western Virginia and North Carolina, the easternmost sections of Kentucky and Tennessee, and the northern tip of Georgia.
Despite their large historic range, the current distribution of rusty patched bumble bees consists of disjunct populations throughout the Midwestern and eastern United States. They currently inhabit only 42 counties in 10 U.S. states across 6 ecoregions. Rusty patched bumble bees are presumed absent from Ontario and Quebec, Canada. They are considered extirpated from much of Wisconsin, with only a few sightings in southern WI since 2012. There have also been fewer reported observations in northern Illinois. Sightings of rusty patched bumbles bees have historically been noted throughout much of the Appalachian Mountains in Virginia, but they have only been recently observed in 5 VA counties: Augusta, Bath, Fauquier, Highland, and Rockingham. There are also recent observations of rusty patched bumble bees in southern Maine and in Tennessee, around the Great Smoky Mountains. Currently, the largest known populations of rusty patched bumble bees are southwest of Lake Michigan, in Indiana, Ohio, and Illinois. However, these populations are experiencing rapid declines. ("Distribution and habitat use of the rusty-patched bumble bee (Bombus affinis) and the yellow‐banded bumble bee (Bombus terricola) in Ohio", 2019; Hatfield, et al., 2015; "Monitoring and habitat assessment of declining bumble bees in roadsides in the Twin Cities metro area of Minnesota", 2019; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016; Wood, et al., 2021)
Rusty patched bumble bees live in nests underground, often in the abandoned burrows of small mammals such as chipmunks or squirrels (family Sciuridae) and mice or voles (family Muridae). Rusty patched bumble bees are most commonly found in burrows as deep as 1.2 m below the soil surface. They dig their own entrance and exit holes, which are around 2 to 6 cm in diameter. Rusty patched bumble bees build their nests in unused, undisturbed burrows. They tend to select burrows that are well insulated and surrounded by high levels of floral diversity. Rusty patched bumble bees are habitat generalists, using a variety of landcover types so long as their nests are within 10 km of native flowers from April to September. There is no known information regarding the range of elevations at which rusty patched bumble bees live.
Rusty patched bumble bees build nests with openings that may be obscured by pieces of grass, moss, or stones. Their nests appear unstructured compared to the highly organized nests of species such as European honeybees (Apis mellifera). Rusty patched bumble bee nests are comprised of wax cells connected to each other in bunches. Their cells are beige and typically spherical, with an opening on either the top or bottom. Rusty patched bumble bee queens lay one egg in each cell. Larvae develop and pupate in these cells and emerge as adults. Cells are around 1 cm in diameter, but vary in length depending on the size of the larvae. Cells that contain developing workers and drones are an average of 1 cm long, whereas cells containing developing reproductive females (also called gynes) are an average of 2 cm long. Rusty patched bumble bees also build wax honey pots, which look almost identical to larval cells. Honey pot cells are filled with digested nectar that are used as food supplies for queens and developing larvae. During early spring, rusty patched bumble bee gynes first establish honey pots to feed themselves and their first brood of developing eggs.
Rusty patched bumble bees rarely form nests above ground, although colonies in urban and suburban areas have been observed to nest in grass clumps in open fields, or in the concrete foundations of houses. Rusty patched bumble bee gynes overwinter in shallow holes, detritus piles, or fallen logs in woodland areas, and seek out new nesting sites in early spring. Gynes often select nesting sites along ecotones between forests and native grasslands. As a result, high quality habitat for rusty patched bumble bees consists of woodlands for overwintering gynes and grasslands for colonies active between spring and fall.
Rusty patched bumble bees build their nests in loose, rich, well-drained soils that protect colonies from harsh weather and low temperatures. Rusty patched bumble bees are adapted to temperate climates; they cannot endure prolonged periods with temperatures above 35 ºC. They usually nest in shaded areas, where the ground is not exposed to as much solar radiation. Rusty patched bumble bees occasionally nest in marshes, wet woodlands, or suburban gardens. They are experiencing habitat loss throughout their range as urban and agricultural development replaces native prairies. Consequently, an increasing number of rusty patched bumble bee colonies are located in urban and suburban areas. For example, a 2019 study from Minnesota found that the landcover within 1 km of rusty patched bumble bee nests is comprised of 75 to 100% developed land, 5 to 8% forest cover, and 1 to 5% native grassland. In Ohio, an estimated 60% of nest sites are located in forest reserves or parks, while the remaining 40% are distributed along roadsides, on residential properties, or on grassy fields maintained by humans (e.g., golf courses, athletic fields). (Boone, et al., 2022; "Distribution and habitat use of the rusty-patched bumble bee (Bombus affinis) and the yellow‐banded bumble bee (Bombus terricola) in Ohio", 2019; Mola, et al., 2021; "Monitoring and habitat assessment of declining bumble bees in roadsides in the Twin Cities metro area of Minnesota", 2019; "Pollination ecology at Loyola University Retreat and Ecology Campus (LUREC) and at other Monarch waystations", 2017; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016)
Rusty patched bumble bees range in body mass from 0.02 to 0.80 g. Body mass is directly related to body size, which varies depending on age, sex, and social role. Rusty patched bumble bee queens are 19 to 23 mm long and 9.5 to 11 mm wide, whereas female drones are 10 to 15mm long and 5 to 9 mm wide, and males are 13 to 17 mm long and 5 to 7 mm wide. Data on the wingspan length of rusty patched bumble bees is limited, and measurement methods are variable, leading to inconsistent results.
Rusty patched bumble bees are covered in relatively long hairs compared to other bumble bee species (genus Bombus). These hairs insulate them and allow them to tolerate cold temperatures in early April and late September. The hairs on their heads are entirely black, and the lateral and dorsal hairs on their thoraxes are pale yellow, with a brownish or blackish patch between their wings. Rusty patched bumble bee abdomens have 6 sections, denoted as T1 to T6 from anterior to posterior, respectively. Worker bees (non-reproductive females) vary slightly in their abdominal colors; their T1 to T3 regions may be entirely yellow, yellow with an orange band through the T2 region, or entirely reddish orange. However, all drones have solid black coloration in the T4 to T6 regions. Queens lack reddish-brown coloration on their T1 to T3 regions and instead are dusty yellow with black T4 to T6 regions. Male drones have longer, thinner bodies that are more ovoid than spherical in shape. Their abdomens are colored almost identically to worker bees, ranging from entirely dusty yellow to entirely reddish orange in the T1 to T3 regions and completely black through the T4 to T6 regions. However, the most common color morph among rusty patched bumble bee workers and drones is dusty yellow on the T1 and T3 regions, with a reddish-orange band running dorsally along the T2 abdominal region and black T4 to T6 regions.
Rusty patched bumble bees have short, stout heads with short tongues. They have two large, compound eyes on either side of their heads and three simple eyes, called ocelli, in a line on the anterior side of their heads. Rusty patched bumble bees have a pair of bent antennae comprised of 3 main parts: the scape, located at the base, the pedicel, where the genicular bend occurs, and the flagellum, which is approximately twice the length of the scape and consists of repeating segmented units. Females have 10 flagella segments whereas males have 11. Compared to other bumble bee species, rusty patched bumble bees have relatively large clypei (plural of clypeus, a large facial plate just dorsal to the mandibles). Rusty patched bumble bees have thoraxes with two large forewings, two small hindwings, and three legs on either side. On their hind legs, the medial sides of their tibias lack hair and are grooved. These areas are called corbiculae, or pollen baskets, and function to transport pollen from flowers back to nests.
Rusty patched bumble bees exist in sympatry with other bumble bee species that are similar in appearance, including common eastern bumble bees (Bombus impatiens) and American bumble bees (Bombus pensylvanicus). Common eastern bumble bees are approximately the same size as rusty patched bumble bees and also have abdomens with dusty yellow T1 to T3 and black T4 to T6 abdominal regions. However, common eastern bumble bees lack reddish-orange coloration on the T2 region, which is present in most rusty patched bumble bees. Furthermore, while both species have dark bands across the thorax between the bases of their wings, these dark bands are more prominent and “V”-shaped in rusty patched bumble bees. American bumble bees are also similar in size compared to rusty patched bumble bees, but they have noticeably different coloration; their thoraxes and their T1, T5, and T6 abdominal regions are fully black. American bumble bees also have yellow on their T2 to T4 abdominal regions and lack reddish-orange coloration on their bodies. (Colla and Packer, 2008; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016; Williams, et al., 2014)
Rusty patched bumble bees live in eusocial colonies, with one female that is responsible for laying eggs (queen) and many females that do not reproduce (workers). Individuals exhibit complete metamorphosis, hatching as larvae and pupating before developing into their adult stage. Rusty patched bumble bees exhibit haplodiploidy, meaning members of the colony can have one set of chromosomes (males) or two sets of chromosomes (females). Queens mate with males in the fall and store sperm over winter, to be used the following spring and summer. Queens can lay fertilized eggs, which develop into females, or unfertilized eggs, which develop into males. Queens lay fertilized eggs that develop into workers throughout spring and summer. Later in summer, queens lay fertilized eggs that instead develop into new queens (gynes) and they also lay unfertilized eggs that develop into males. By late summer and early fall, gynes and males disperse from nests to mate with individuals from other colonies. By winter, all colony members die, with the exception of gynes, which enter diapause throughout winter and establish new colonies in the spring.
Rusty patched bumble bee queens lay their eggs inside wax cells, which provide protection during the larval and pupal stages of development. Between 3 to 5 days after being laid, larvae hatch from eggs and must be promptly provided with nectar and pollen. Pollen is important during larval stages, as the proteins in pollen are essential for growth. The amount of pollen that larvae receive are directly related to their maximum size as fully developed adults. Growing larvae depend on workers to feed them pollen from pollen reserves and nectar pots, although queen bees are responsible for feeding their first brood of larvae in the spring. Larvae have white, cylindrical bodies covered in wrinkles and they lack eyes, legs, and wings. Larvae develop through 4 instars over the course of around 2 weeks, during which they grow in size and develop a functioning digestive system. As larvae begin to pupate, the openings of their wax cells are sealed by worker bees. Larvae take around 7 to 10 days to pupate, depending on their future role in the colony (i.e., male, worker female, gyne).
Newly metamorphosed adult rusty patched bumble bees remain in their enclosed cells until the hairs on their legs, called setae, have fully dried. Adults are considered to be in their "callow stage" upon emerging from their wax cells. During the callow stage, adults move slowly, are not aggressive, and cannot use their wings. Callow adults remain in their nests to feed and gain energy. After 1 to 3 days, they are considered fully-fledged adults and begin to perform typical adult functions, depending on their role in the colony. Adult rusty patched bumble bees do not shed their exoskeletons, and thus do not grow further once they reach adulthood. The size of growing pupae has not been specifically measured, but adult workers measure 10 to 16 mm long, queens measure 20 to 22 mm long, and males measure 13 to 17 mm long.
There are 17 major pupal stages, defined as P0 to P16, that all true bumble bees (genus Bombus) undergo before emerging as adults. Although variation in pigmentation and size is species-specific, the characteristics of pupal stages are relatively consistent across all Bombus species. The process of pupation lasts around 160 to 180 hours for workers, 189 hours for males, and 243 hours for gynes. Each pupal stage lasts roughly 10 hours for workers, 13 hours for males, and 15 hours for gynes. However, larval size and incubation temperature (ideally 32 ºC) also impacts the duration of pupation. During the first stage of pupation (P0), new pupae possess the basic characteristics of adult bees including heads, thoraxes, and abdomens. During P0, abdominal segments 8 to 10 begin to retract. This retraction differentiates the two sexes based on the presence of stingers (females only) and genitalia located in the hypogastric region. Their thoraxes also begin to fuse with their first abdominal segments to form propodea: large sclerite plates that give bumble bees their distinctive tapered "waist". In the second stage (P1), abdominal segments 8 to 10 finish retracting and the propodeum fully forms. At this point, female pupae have six segments in their abdomens whereas males have seven. In the third stage (P2), the most distal region of their legs, called basitarsi, flatten and darken from their previously clear and cylindrical appearance. This basitarsal flattening creates recognizable shapes on the hind legs, which eventually function to collect and press pollen into pellets for food. In the fourth stage (P3), bumble bee pupae gain pigmentation in their eyes, which are white or pale yellow beforehand. Eye pigmentation begins to develop as small specks, which range from orange to brown in color. In the fifth stage (P4), pupae also develop orangish-pink coloration in their eyes. In the sixth stage (P5), the individual eyes (ommatidia) within their compound eyes develop a hexagonal structure and their compound eyes develop an overall darker orange coloration. In the seventh stage (P6), pupae have eye pigmentation that is dark orange or red in appearance. In the eighth stage (P7), the reddish eyes darken to attain a maroon pigmentation. The P7 stage is considered one of the longest stages of the pupation process, although few external changes occur. In the ninth stage (P8), larvae develop pinkish hues in their thoracic region, also called the mesosoma. Their compound eyes also become uniformly dark brown in coloration and become uniformly black in the tenth stage (P9). Pupae also develop more body pigmentation in the P9 stage; the pinkish hue of the mesosoma intensifies and becomes red in color, visually separating it from the abdominal region, also called the metasoma. Pupae develop an orangish-tan coloration on their tarsal claws, wing bases, proboscises, and mandibles, as well as other regions of their body. Pupae reach the P9 stage after around 90 hours, which marks the halfway point of bumble bee pupation. In the eleventh stage (P10), the metasoma starts to melanize, turning a darkish peppered color. Stripes begin to appear on pupal sternite (ventral) plates and, by the twelfth stage (P11), pupae gain prominent stripes across their entire metasomal regions, including the tergite (dorsal) and sternite (ventral) regions. The frontal lines across their heads also become speckled during P11. In the thirteenth stage (P12), pupae have prominent stripes that wrap around their bodies. They also develop black pigmentation in their setae. In the fourteenth stage (P13), larvae develop darker pigmentation on their proboscises and antennae. Their heads also continue to melanize and their metasomal region is fully pigmented, with melanization covering at least half of their tergites and sternites. In the fifteenth stage (P14), pupae develop dark coloration on the entirety of their heads, including their antenna, mandibles, clypei, and para-ocular regions. In the sixteenth stage (P15), pupae have developed adult coloration in all parts of their bodies except their legs and proboscises, which remain a dark orangish color. In the seventeenth stage (P16), their legs begin to twitch and their pupal cuticle begins to wrinkle on their heads, mandibles, and mesosomal regions. The pupal cuticle degrades around their legs and metasomal regions, revealing their adult cuticle underneath. By the end of the P16 stage, pupae molt their entire cuticle and are considered fully developed adults. (Cnaani, et al., 2002; Tian and Hines, 2018)
Rusty patched bumble bee queens are solitary from late fall to early spring and form eusocial colonies through spring and summer. Starting in mid-to-late summer, queens lay eggs that develop into reproductive males (drones) and new queens (gynes), both of which leave their nests to mate with individuals from different colonies. Before gynes and drones mate, they perform a courtship dance and then perform a copulatory flight, during which insemination occurs. After successfully mating, gynes store sperm from drones and enter diapause through the winter. When temperatures warm in spring, gynes locate nest sites, construct nests, and establish preliminary stores of pollen and nectar. They then use stored sperm to internally fertilize their eggs and rear their first brood of workers. Once workers develop into adults, the queen lays more eggs while the workers care for larvae and forage for more pollen and nectar.
Rusty patched bumble bee queens secrete chemicals from their labial glands to prevent workers from laying eggs. In cases where colonies lose their queen, workers are capable of producing viable eggs, since the chemicals that restrict oocyte development are no longer present. However, since they never participate in copulatory flights, workers can only lay unfertilized eggs, which develop into haploid males. In the absence of a queen, workers can lay eggs as soon as 8 days after emerging from their pupal stage. Queens maintain a reproductive monopoly until mid-to-late summer, at which point successful colonies can consist of several hundred individuals. Queens begin to lay unfertilized eggs to produce drones and downregulate the production of certain chemicals, which restrict worker reproduction and prevent fertilized eggs from developing into gynes. By late summer or early fall, gynes and drones begin to develop and hatch, and some workers also begin to exhibit reproductive activity and lay unfertilized eggs.
All insects in the order Hymenoptera (i.e., bees, wasps, sawflies, ants) possess labial glands that aid in chemical signaling. Little is known about the specific role of labial glands in rusty patched bumble bees. Much of the information on labial gland function in bumble bees (genus Bombus) originates from research on buff-tailed bumble bees (Bombus terrestris). In this species, the labial glands of infertile females produce more fatty ester compounds compared to fertile females. Is is possible that, by production higher amounts of esters, females can signal that they are infertile and thus avoid aggression from competitive, fertile females.
The function of labial glands in bumble bee males (drones) has been more widely studied compared to their function in females. Drones release pheromones from their labial glands, which they use to mark territories and attract mates. The chemical composition and concentration of male pheromones varies among bumble bee species, suggesting they are used for intraspecific interactions. Drones exhibit distinctive copulatory behaviors in late summer and fall. These behaviors include pheromone marking, patrolling specific flight paths, and waiting by nest entrances for gynes. Across all bumble bee species, male pheromones can disperse across long distances and play key roles in species-specific reproductive behavior. Drones mark their flight paths with pheromones between morning and midday, and then regularly patrol their flight paths throughout the day. Their pheromones contain volatile chemicals, which attract unmated gynes of the same species. Once gynes detect these pheromone paths, they come to rest on nearby landmark sites, such as stones, stumps, fences, or other prominent geographical features. Male pheromones are not solely responsible for copulation behavior; females release pheromones that are also essential for sex recognition, and species-specific copulatory behaviors.
Each species of bumble bee secretes pheromones with a specific blend of compounds, which prevents interspecific breeding. There is little information on the chemical composition of reproductive pheromones in rusty patched bumble bees specifically. However, the pheromones of buff-tailed bumble bees have been thoroughly analyzed, and may share some similarities with the compounds used by rusty patched bumble bees. The pheromones of buff-tailed bumble bee females consist of 79 compounds, 53 of which have been identified and 26 of which remain unidentified. Female pheromones are mostly comprised of fatty compounds and hydrocarbons, with carbon chains ranging in length from 21 to 33 atoms. However, the chemical composition of female pheromones varies intraspecifically depending on age, and role in the colony (i.e., queen, worker, gyne). The hydrocarbon known as pentacosane (C25) potentially plays a major role in promoting worker sterility. In studies on buff-tailed bumblebees, workers exposed to pentacosane showed higher rates of oocyte resorption, defined as the absorption of egg cells back into the body. Therefore, workers exposed to high levels of pentacosane exhibit less egg development. The presence of queen bumble bees negatively affects the ovary and oocyte development of workers, suggesting the compounds that queens release from their labial glands include pentacosane and possibly other chemicals that reduce ovary development. (Krieger, et al., 2006; Padilla, et al., 2016; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016; Valterová, et al., 2019)
Rusty patched bumble bees are semelparous and monogamous. Between late July and late October, males (drones) and newly hatched queens (gynes) depart their nests to copulate with individuals from other colonies. Drones die soon after mating, whereas gynes seek out thermally stable locations and enter diapause for the winter. Gynes store sperm from males in specialized organs, called spermathecas, and use stored sperm the following spring and summer. Gynes are the only individuals to enter diapause throughout the winter; old queens, workers, and drones all die by the end of fall. Overwintering gynes resume activity around mid-March, when temperatures begin to warm. They search for nesting sites where they can establish a colony, then spend early spring stockpiling pollen and nectar. Gynes then use stored sperm to fertilize their eggs and lay their first brood. The new queens use stored pollen and nectar to rear their first brood, which develop into worker females that then perform the tasks of foraging for food and rearing successive broods. The number of eggs that queens lay in each brood varies depending on the health of the colony. Factors that can affect brood size include the amount of food and space available, age of the colony, and nest temperature.
Queens lay their second brood soon after their first brood reaches maturity, which takes around 5 weeks. Larvae hatch from eggs approximately 2 days after queens lay them. Larvae remain in wax cells and are fed pollen and nectar for around 2 weeks. Larvae are then sealed into their wax cells and begin the process of pupation, which lasts around 2 weeks. Finally, pupae emerge from their wax cells as callow adults, which spend 1 to 3 more days in their nests before their wings fully develop and they can contribute to the colony. The time it takes for adults to develop from eggs can range from 4 to 6 weeks depending on the conditions in the nest. The ideal incubation temperature for rusty patched bumble bees is between 29 and 32 ºC. Incubation lasts longer at colder temperatures and developing young can die at temperatures above 32 ºC. Nest humidity typically ranges from 50 to 65%, although the effects of changing humidity on larval development are unclear. Incubation speed also depends on larval sex and future role in the colony. Worker development is an average of 4 days shorter than gynes or drones, as workers tend to be smaller and have less complex reproductive anatomy. (Krieger, et al., 2006; Padilla, et al., 2016; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016; Tian and Hines, 2018; Valterová, et al., 2019)
Rusty patched bumble bee males provide no parental investment beyond the act of mating. Queens exhibit extended parental investment, especially for their first brood of eggs. In May, after emerging from diapause, new queens seek out nesting sites and establish their own colonies. Queens forage for food and construct wax cells early in spring, then lay their first brood of fertilized eggs. Queens spend around 5 weeks providing developing larvae with food and maintaining the nest. However, once their first brood reaches maturity, queens provide no parental care for successive broods beyond the act of laying eggs. The first brood of eggs develop into workers, foraging for food and providing care for later broods of eggs. (Krieger, et al., 2006; Tian and Hines, 2018; Valterová, et al., 2019)
Rusty patched bumble bees live around a year at most, although lifespan depends on sex and role in the colony. Queens have the longest lifespan, living around a year if they successfully mate or a month if they are unsuccessful. Rusty patched bumble bee workers life anywhere from a few weeks to a few months, averaging approximately 28 days. Rusty patched bumble bee males live an average of 2 weeks after emerging as adults. They spend their time seeking mates and die shortly after mating.
Rusty patched bumble bees are not kept in captivity, so there is no information on captive lifespans. ("Petition to list the rusty patched bumble bee Bombus affinis (Cresson), 1863 as an endangered species under the U.S. Endangered Species Act", 2013; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016; Tian and Hines, 2018)
Rusty patched bumble bees are eusocial, with a social hierarchy that typically involves one egg-laying queen, many female workers, and reproductive males (drones) and females (gynes) that hatch later in the active season. However, when colonies reach large numbers, workers start to compete with queens for reproductive rights. Competition can begin as soon as a month after queens establish their colonies, depending on the growth rate of the colony. In such cases, workers challenge queens with aggressive behavior, although cases of aggression are rare and not well understood. In particularly small colonies, worker bees may begin to attack their queens while they are laying eggs by biting their legs and bodies. Aggressive workers may even begin to lay eggs that queens destroy and eat if they detect them. If queens die unexpectedly, the lack of queen pheromones that typically restrict worker reproduction are absent, meaning workers are capable of laying eggs. Workers fight amongst themselves for hierarchical rights to lay eggs. They compete by rearing on their hind legs and using their mandibles and forelegs to grapple until one retreats. Following competition, some workers begin laying eggs while other workers continue to raise larvae and forage for food. However, since worker bees do not have stored sperm, they are only capable of producing unfertilized eggs and thus only male offspring.
Rusty patched bumble bee activity is most heavily influenced by ambient air temperatures. They are primarily active between March 15 and October 10, though at colder climates and at latitudes above 42 ºN they exhibit a shorter active season, between April 10 and October 10. Rusty patched bumble bees fly in a range of weather conditions and are able to tolerate colder temperatures compared to other pollinators due to their thick, furry bodies. However, they do not fly in rainy, foggy, or freezing conditions. Rusty patched bumble bees remain active around dawn and dusk at temperatures no lower than 4 ºC in early March and October. Workers cease foraging activities in fall only when native flowers begin to die and food sources become scarcer. (Cnaani, et al., 2002; Colla and Packer, 2008; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016; Wood, et al., 2021)
There is limited information regarding home range or territory sizes of rusty patched bumble bees. Workers forage in a 1 km^2 area, on average, centered on their nests. However, colony ranges have been reported to be as large as 10 km^2. Tracking the flight paths of specific bees across long distances is logistically difficult, and thus there is little information regarding the true home range of rusty patched bumble bees. Home range size varies between colonies depending on nearby floral diversity and land cover types. Rusty patched bumble bees are generally docile and non-aggressive compared to honey bees, wasps, ants, and other hymenopterans (order Hymenoptera). They only defend the territory immediately surrounding their nests and only when provoked by predators or other disturbances. (Cnaani, et al., 2002; Colla and Packer, 2008; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016; Wood, et al., 2021)
Rusty patched bumble bees rely on visual, chemical, tactile, and electrical stimuli to perceive their environment. The surface of the earth and objects on the ground typically carry a negative charge, while the atmosphere carries a positive charge. Because rusty patched bumble bees fly when foraging, they often become positively charged. Their antennae and filiform hairs on their heads allow rusty patched bumble bees to detect the electrical fields that are created when their positively charged bodies approach grounded objects with negative charges. From this, they receive relevant sensory information about their surroundings. Rusty patched bumble bees are even capable of distinguishing the shape and size of stationary objects based on the characteristics of electric fields. The filiform hairs that rusty patched bumble bees have are capable of detecting weak electrical currents, at frequencies as low as 3.8 kHz. Their filiform hairs can also detect vibrations and other pressure gradients in the air. Furthermore, the pedicel regions of their antennae have organs, called Johnston's organs, that allows bumble bees to "hear" vibrations transmitted in the air by detecting oscillations in atmospheric particles.
Rusty patched bumble bees rely on their vision to navigate their environment and identify foraging sites. Rusty patched bumble bees have five eyes: two large, compound eyes and three simple eyes, called ocelli. Their two large, compound eyes consist of approximately 6,000 individual optical units, called ommatidia, each of which are around 26 µm in diameter. Each ommatidium consists of hexagonal subunits and translucent light receiving cylinders that contain photopigments. These pigments allow rusty patched bumble bees to perceive blue, green, and UV wavelengths, but not red wavelengths. Because of this limited color vision, bumble bees visit blue and violet flowers more frequently than flowers of other colors. Certain flowers have patterns on their corollas that reflect UV wavelengths that serve as "nectar guides", directing bees and other pollinators to their anthers and stigmas. Rusty patched bumble bees also have a region in their compound eyes called the dorsal rim area (DRA), located along the outer perimeter of each eye. The DRA is responsible for detecting light polarization, although it has unknown practical uses in rusty patched bumble bee foraging behavior. In addition to flower color, rusty patched bumble bees decide which flowers to visit based on flower saturation, size, shape, the contrast of the corollas, and flower cluster density.
Rusty patched bumble bees rely heavily on chemical cues for detecting food sources. Flowers release mixtures of volatile organic compounds (VOCs) that act as chemical signals to bees. The ratios of VOCs released by flowers communicate their relative suitability as a source of nectar and pollen. Rusty patched bumble bees detect VOCs with chemoreceptors in their antennae. Different VOCs communicate different plant properties, such as antimicrobial or antiviral features. Some VOCs also serve to repel or attract certain insects. Rusty patched bumble bees are capable of distinguishing the VOC profiles of plant species that provide suitable foraging resources. For example, the compound geraniol encourages foraging behavior and encourages more rusty patched bumble bee workers to leave the nest, especially when food resources are low.
Rusty patched bumble bees also use chemical stimuli to communicate with conspecifics. Individuals leave unique pheromone trails as they move around. These pheromones are likely secreted from tendon glands, located on their legs, and are used to mark important landmarks, such as nest entrances, flower patches, and mating areas. During the breeding season, rusty patched bumble bee males (drones) repeatedly travel specific paths, which they mark with their unique pheromone signatures. Along their paths, males frequently revisit "buzzing places", which are typically prominent landmarks (e.g., large trees, stumps, rocks, etc.). When reproductive females (gynes) detect the pheromone trail of a drone, they fly until they reach a buzzing place and land, waiting for the drone to return along its path. Gynes also emit their own reproductive pheromones from mandibular glands while they wait at buzzing places, which further attracts nearby drones. In addition to mating communication, rusty patched bumble bees use chemicals to communicate within their colonies. For example, non-reproductive worker females release specific compounds to communicate their infertility and thus avoid competition with queens or reproductive workers. Furthermore, queens release chemicals that, at high concentrations, promote infertility in worker bees and inhibit the development of gynes. (Colla and Packer, 2008; Macior, 1966; Macior, 1967; Meyer-Rochow, 2019; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016; Sutton, et al., 2016)
Rusty patched bumble bees derive all their nutrients from nectar and pollen; nectar provides carbohydrates and pollen provides lipids and proteins. Without a constant and stable supply of nectar, rusty patched bumble bees quickly starve to death. Due to this high demand for nectar, they most frequently forage from flowers with high sugar content and large nectar rewards. Proteins from pollen are also important for rusty patched bumble bees, as pollen provides all the amino acids that they need to survive. Pollen is also a supply of sterols, volatiles, and other organic compounds that aid in hormone production, communication, and protection against pathogens. Different flowers contain different pollen types, each of which contains a different ratio of proteins and lipids (P:L). Rusty patched bumble bees regulate the intake of pollen depending on their dietary demands and the nutritional values of different pollen types. A study from 2016 found that common eastern bumble bees (Bombus impatiens) typically select flowers with a P:L ratio of 10:1 to 14:1 but will adjust to a high-lipid diet to achieve sufficient levels of protein. It is likely that rusty patched bumble bees select flowers with similar P:L ratios. Pollen is essential because the amount of pollen a colony obtains directly impacts the number of queens it can produce. Rusty patched bumble bees actively seek pollen with higher-quality amino acids and ideal P:L ratios. Although the flowers that rusty patched bumble bees select have higher levels of pollen, lipids are also important for the production of beeswax. Rusty patched bumble bees have wax glands on the ventral side of their abdomens that produce beeswax, which is ultimately used to build nests and wax cells to protect larvae.
Rusty patched bumble bees are eusocial, with a caste of workers that forage for the entire colony, storing reserves of nectar and pollen in wax cells. However, queens forage for themselves and their young early in spring, before their first brood of eggs develop into workers. Also, adult males (drones) forage for themselves after they depart the colony to find mates.
Rusty patched bumble bees have a long foraging season compared to other bumble bee species. They are active from April to September and are adapted to foraging at cool temperatures and in low-light conditions (i.e., dusk and dawn). In April, rusty patched bumble bees obtain food from ephemeral spring flowers within 1 km of their nests, often in forested areas. The time that gynes emerge from diapause coincides with the early blooms of flowering plants. Rusty patched bumble bees are classified as short-tongued bees, with an average tongue length of 5 to 6 mm. Because their tongues are relatively short, they cannot reach nectar inside long, tubular flowers with narrow corollas and must obtain nectar from shallow, open flowers. However, rusty patched bumble bees are considered to be generalists and will pollinate a wide variety of plant species with shallow flowers, regardless of whether they are native or introduced. Rusty patched bumble bees are known to feed on plant species and orders, including Virginia bluebells (Mertensia virginica), columbines (genus Aquilegia), beebalms (genus Monarda), nightshades (genus Solanum), giant hyssops (genus Agastache), milkweeds (genus Asclepias), sweet yellow clovers (genus Melilotus), sow thistles (genus Sonchus), tickseeds (genus Coreopsis), bleeding hearts (genus Dicentra), sunflowers (genus Helianthus), willows (genus Salix), asters (family Asteraceae), and peas (family Fabaceae). Rusty patched bumble bees also forage and pollinate a wide variety of commercially and agriculturally important crops, such as tomatoes (Solanum lycopersicum), currants (genus Ribes), cranberries and blueberries (genus Vaccinium), peppers (genus Capsicum), stone fruits (genus Prunus), and squashes (genus Cucurbita).
Over the past century, despite the rapid population decline of rusty patched bumble bees, no significant changes in dietary composition have been recorded. (Colla and Packer, 2008; Macior, 1966; Macior, 1967; Macior, 1978; "Petition to list the rusty patched bumble bee Bombus affinis (Cresson), 1863 as an endangered species under the U.S. Endangered Species Act", 2013; "Pollination ecology at Loyola University Retreat and Ecology Campus (LUREC) and at other Monarch waystations", 2017; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016; Simanonok, et al., 2020; Vaudo, et al., 2016; Wood, et al., 2019; Wood, et al., 2021)
Rusty patched bumble bees frequently serve as prey for goldenrod crab spiders (Misumena vatia), which prey on various bumble bees (genus Bombus) and honey bees (genus Apis) that visit goldenrod plants (genus Solidago). Goldenrod crab spiders are camouflaged well with the goldenrod flowers they sit on, which allows them to ambush bees and other goldenrod pollinators. However, research on bumble bees has shown that they can potentially avoid flowers that have crab spiders on them. Through learned behavior, if bumble bees encounter or see crab spiders on certain plants, they visit those plants less frequently.
Another common predator of rusty patched bumble bees are bee-killer wasps, also called beewolves (genus Philanthus), which are capable of attacking around 200 bees each day. Areas with increased beewolf activity tend to have a decreased abundance of bumble bees and a corresponding reduction in pollinated plants. Decreased bumble bee densities are not only due to direct predation by beewolves, but also due to avoidance behaviors exhibited by bumble bees.
Rusty patched bumble bees have aposematic patterns of alternating yellow and black coloration, which deters many potential predators. Certain combinations of light and dark colors, such as black and yellow, are common throughout the animal kingdom as a method of communicating toxicity. For instance, rusty patched bumblebees have stingers at the posterior tip of their abdomens that can inject venom stored in venom sacs. Rusty patched bumble bee venom contains a combination of histamines, proteins, and irritants that directly affect animal skin and circulatory systems. Unlike honey bees, which have barbed stingers, bumble bees possess smooth stingers that do not get stuck in the objects they sting. This allows bumble bees to sting multiple times without dying. (Dukas, 2005; Dukas and Morse, 2003; Morse and Fritz, 1989)
Rusty patched bumble bees eat nectar and pollen, and thus pollinate a variety of flowering species. They are also a source of food for predators, such as goldenrod crab spiders (Misumena vatia) and bee-killer wasps (genus Philanthus).
Rusty patched bumble bee colonies are parasitized by cuckoo bumble bees (Bombus ashtoni), which are not considered "true bumble bees" but rather a social parasite. Cuckoo bumble bees invade the functioning nests of true bumble bee species and take over reproductive control of the colony. Female cuckoo bumble bees locate nests by olfaction (nests with shorter entrance tunnels are more easily discoverable) and kill resident queens. They then lay their own eggs and exploit the true bumble bee workers, relying on them to provide food and rear young. Female cuckoo bees can be identified by their lack of pollen-carrying baskets. True bumble bee workers may identify parasitic queens and attempt to attack them. In other instances, true bumble bee workers raise cuckoo larvae without noticing. If cuckoo queens die, true bumble bee workers stop caring for cuckoo young and begin to lay their own eggs. (Fisher, 1983; Morse and Fritz, 1989)
Rusty patched bumble bees have a large positive impact on local economies, as they pollinate a variety of crops and native plants. Rusty patched bumble bees are plant generalists, and indiscriminately pollinate native and non-native species, making them effective pollinators of non-native crops. Rusty patched bumble bees obtain an estimated 12% of their pollen and nectar from species of peas (family Fabaceae) and act as important pollinators for a variety of other commercially grown crops such as tomatoes (Solanum lycopersicum), currants (genus Ribes), cranberries and blueberries (genus Vaccinium), peppers (genus Capsicum), stone fruits (genus Prunus), and squashes (genus Cucurbita). (Colla and Packer, 2008; "Distribution and habitat use of the rusty-patched bumble bee (Bombus affinis) and the yellow‐banded bumble bee (Bombus terricola) in Ohio", 2019; Macior, 1967; "Petition to list the rusty patched bumble bee Bombus affinis (Cresson), 1863 as an endangered species under the U.S. Endangered Species Act", 2013; "Pollination ecology at Loyola University Retreat and Ecology Campus (LUREC) and at other Monarch waystations", 2017; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016)
Rusty patched bumble bees possess stingers with weak, protein-based venom. Some people are allergic to their venom, although it is rare for anaphylaxis to occur due to their stings. Symptoms of bumble bee venom people who are not allergic include localized redness, swelling, mild pain, and itchiness. However, rusty patched bumble bees pose very little threat to humans, and will not sting unless provoked or their nests are threatened. (Hoffman and Jacobson, 1996)
Rusty patched bumble bees are considered “Critically Endangered” by the IUCN Red List, “Endangered” on the U.S. federal list and the State of Michigan list, but have no special status on the CITES list.
According to the IUCN, there was a 92.54% decline in the abundance of rusty-patched bumble bees between the 1990s and 2010s. Rusty patched bumble bee populations are decreasing in size rapidly due to several factors, including urbanization, habitat fragmentation, and climate change. In urban and suburban areas, reports show that areas with increasing proportions of paved surfaces and man-made structures correlate with decreased rusty patched bumble bee nest densities. Rusty patched bumble bees are also threatened by land use for agriculture, including livestock ranching, monoculture farming, and timber harvesting. Livestock grazing poses direct and indirect negative impacts on rusty patched bumble bee populations. Domestic cows (Bos taurus) and sheep (Ovis aries) directly alter potential bumble bee habitat by compressing topsoil, grazing native plants, and trampling nesting sites. Furthermore, agricultural land cover replaces forests, prairies, and grasslands that are more suitable for rusty patched bumble bees. In many cases, agricultural practices also involve genetically modified crops and hybridized flowers. Such hybridized flowers often do not have functional reproductive systems, and thus do not produce the same abundance of pollen sources as unmodified species.
Rusty patched bumble bees are also negatively impacted by monocultural farming practices. Rusty patched bumble bees require areas with a wide diversity of plant species so that there are blooming flowers from spring to fall, so fields with only one plant species fail to provide sufficient resources and reduce colony reproductive success. Furthermore, the dangerous pesticides that some farmers and homeowners use on their crops and gardens can inadvertently harm rusty patched bumble bees. They can be poisoned by pesticides while foraging on sprayed plants, or nests can be affected by contaminated groundwater and acid rain. Climate change also impacts rusty patched bumble bees by increasing the incidence of droughts, flooding, and temperature extremes. Rusty patched bumble bees can drown if their underground nests become waterlogged, and extreme temperatures make it difficult for rusty patched bumble bees to forage, as they are ectothermic and cannot regulate their own body temperature. Additionally, as the timing of frosts in fall and spring shifts, rusty patched bumble bees entering or emerging from diapause may do so prematurely or not soon enough.
There are currently efforts to list rusty patched bumble bees as critically endangered, both nationally and internationally. There are also conservation projects focused on restoring unfragmented habitat for rusty patched bumble bees. Movements to ban dangerous pesticides are based on evidence that they affect rusty patched bumble bees and a large number of other native species and ecosystems. Furthermore, prescribed burns are a potentially viable tool for restoring native grasslands and prairies, which would provide more habitat for rusty patched bumble bees and other pollinators. (Colla and Packer, 2008; "Distribution and habitat use of the rusty-patched bumble bee (Bombus affinis) and the yellow‐banded bumble bee (Bombus terricola) in Ohio", 2019; "Late summer bumble bee species richness and abundance in Bourbonnais Township, Northeastern Illinois", 2016; "Petition to list the rusty patched bumble bee Bombus affinis (Cresson), 1863 as an endangered species under the U.S. Endangered Species Act", 2013; "Pollination ecology at Loyola University Retreat and Ecology Campus (LUREC) and at other Monarch waystations", 2017; "Rusty patched bumble bee (Bombus affinis) species status assessment", 2016)
Rusty patched bumble bees exhibit sex determination based on locus complementation. Usually, heterozygote bumble bees develop from fertilized eggs into diploid females and hemizygote bees develop from unfertilized eggs into males. However, there are unusual cases where diploid females and haploid males copulate but share a common sex-determining allele. Known as “matched mating”, this common allele causes half the resulting progeny to be homozygous and develop into diploid males rather than diploid females. Matched mating is detrimental, as it reinforces low genetic diversity that is already present.
Reproductive males do not provide as much to colonies as reproductive females, so a high number of male offspring ultimately decreases the potential fitness of colonies. Furthermore, colonies with a high number of males have decreased foraging potential, as female workers are responsible for foraging and raising young. Not only do diploid males negatively affect the productivity of colonies, but they also produce unviable offspring. Male diploidy due to inbreeding can further reduce genetic diversity in a positive feedback loop called an "extinction vortex". ("Rusty patched bumble bee (Bombus affinis) species status assessment", 2016)
Alexander McVicker (author), Radford University, Sierra Felty (editor), Radford University, Karen Powers (editor), Radford University, Galen Burrell (editor), Special Projects.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in landscapes dominated by human agriculture.
having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
helpers provide assistance in raising young that are not their own
a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.
a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
uses electric signals to communicate
the condition in which individuals in a group display each of the following three traits: cooperative care of young; some individuals in the group give up reproduction and specialize in care of young; overlap of at least two generations of life stages capable of contributing to colony labor
parental care is carried out by females
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
Referring to a burrowing life-style or behavior, specialized for digging or burrowing.
An animal that eats mainly plants or parts of plants.
the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.
fertilization takes place within the female's body
marshes are wetland areas often dominated by grasses and reeds.
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats nectar from flowers
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
development takes place in an unfertilized egg
chemicals released into air or water that are detected by and responded to by other animals of the same species
an animal which has a substance capable of killing, injuring, or impairing other animals through its chemical action (for example, the skin of poison dart frogs).
light waves that are oriented in particular direction. For example, light reflected off of water has waves vibrating horizontally. Some animals, such as bees, can detect which way light is polarized and use that information. People cannot, unless they use special equipment.
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.
places a food item in a special place to be eaten later. Also called "hoarding"
living in residential areas on the outskirts of large cities or towns.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
living in cities and large towns, landscapes dominated by human structures and activity.
an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
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