Buff-tailed Bumble Bee

Appearance

"B. terrestris" are pollen-storing bees that generally feed and forage on nectar and pollen. The queen is between 20 and 22 mm long, males range from 14 to 16 mm, and workers from 11 to 17 mm. Workers have white-ended abdomens, and look just like workers of the white-tailed bumblebee, "B. lucorum", a close relative, apart from the yellowish bands of "B. terrestris" being darker in direct comparison. The queens of "B. terrestris" have the namesake buff-white abdomen tip; this area is white as in the workers in "B. lucorum." "B. terrestris" is unique compared to other bees in that their caste of workers exhibit a wide variation in worker size, with thorax sizes ranging from 2.3 to 6.9 mm in length and masses ranging from 68 to 754 mg.

Naming

Female Bee Moths prefer to lay their eggs in the nests of bumblebees. The "A. sociella" larvae will then hatch and feed on the eggs, larvae, and pupae left unprotected by the bees, sometimes destroying large parts of the nest as they tunnel throughout looking for food.While native to Europe, "B. terrestris" has been introduced as a greenhouse pollinator into many foreign ecosystems. The presence of "B. terrestris" is becoming an ecological concern in many communities in which it is not native. It is classified as an "invasive alien species" in Japan. For example, "B. terrestris" has a large niche overlap with local Japanese bee species in terms of flower resources and nest sites. "B. terrestris" queens competing for local underground nest sites are displacing "B. hypocrita sapporoensis". However, "B. pseudobaicalensis", which visits similar flowers but only forms nests above ground, has not seen a rapid decline in population numbers.

In 2008, the Australian government banned the live import of "B. terrestris" into Australia on the grounds that it would present a significant risk of becoming a feral species and thereby present a threat to native fauna and flora. In 2004, this bumblebee was classified as a 'Key Threatening Process' by the Scientific Committee of the New South Wales Department of Environment.

This species was introduced to Chile in 1998. It has since crossed into Argentina, and is spreading at about 275 km per year. Its spread has been detrimental to populations of "Bombus dahlbomii", which is the only bumblebee species native to southern South America. "Bombus terrestris" populations facilitated such massive and immediate population decline of "Bombus dahlbomii" through competition and pathogen introduction/spillover. "Bombus ruderatus", a bee previously introduced in 1982, is also seriously affected. The cause is thought to be the parasite "Apicystis bombi", an organism carried by the buff-tails, but which has no adverse effect on that species.

Distribution

"B. terrestris" is most commonly found throughout Europe and generally occupies temperate climates. Because it can survive in a wide variety of habitats, there are populations in the Near East, the Mediterranean Islands, and Northern Africa as well. Additionally, it has escaped captivity after being introduced as a greenhouse pollinator in countries where it is not native, so this bee is now considered an invasive species in many of these places, including Japan, Chile, Argentina, and Tasmania. Nests are usually found underground, such as in abandoned rodent dens. Colonies form comb-like nest structures with egg cells each containing several eggs. The queen will lay egg cells on top of one another. Colonies produce between 300 and 400 bees on average, with a large variation in the number of workers.

Behavior

Like in most social bees"," there are three main social caste divisions in "B. terrestris." This ensures a division of labor and efficient colony functioning. Queens become the main female individual to reproduce in a future colony. There is only one per colony. Her sole responsibility is to lay eggs after she founds a nest. This fate is determined for larvae that receive more food, have longer instar stages, and higher levels of juvenile hormone biosynthesis. Workers, an entirely female caste, mainly forage for food, defend the colony, and tend to the growing larvae. They are usually sterile for most of the colony cycle and do not raise their own young. Unlike queens and workers, which develop from fertilized diploid eggs, drones, or male bees, are born from unfertilized, haploid eggs. Drones leave the colony shortly after reaching adulthood to find a mate outside the nest. Mating is their sole role in the colony.A solitary queen hatched from her abandoned colony initiates the colony cycle when she mates with a male and finds a nest. She will stay in this nest over winter and then will lay a small batch of diploid eggs in the spring. Once these hatch, she tends the larvae, feeding them with nectar and pollen. When the larvae are grown, they pupate, and about two weeks later, the first workers emerge. This is known as the initiation phase of the colony. Workers forage for nectar and pollen for the colony and tend later generations of larvae. The workers are smaller than the queen, and usually die while foraging in the jaws of predators like birds or robberflies. The foraging range and frequency of workers depends on the quality and distribution of available food, but most workers forage within a few hundred meters of their nest.

This first phase can last a variable amount of time in "B. terrestris", after which a switch point is reached, and the queen begins to lay some unfertilized eggs, which develop into males. When the male drones emerge from the nest, they do not return, foraging only for themselves. They seek out emerging queens and mate with them. The remaining diploid eggs hatch into larvae that receive extra food and pupate to become new queens. The queen can use pheromones to discourage the workers' inclination to invest more in these larvae, thereby ensuring that not too many become queens. The resolution of this worker/queen conflict can be complex and is discussed below. The colony persists until fall in temperate zones and then workers begin to lay unfertilized eggs that if they mature will become males. At this point, outright aggression among workers and between the queen and workers begins. This is a predictable time point that occurs about 30 days into the colony cycle in very temperate climates.

Usually, the worker-queen conflict will force the queen out and the new workers will become queenless. A "false queen" might take control of the colony for a short period. The newly emerged queens sometimes act as workers and help to raise another brood of queens. During this time they daily leave the nest looking for food, during which time they may mate. Eventually they find a site to dig a “hibernaculum” where they will hibernate until the next spring, when they emerge, seek food — primarily to build up their ovaries — and soon seek a site to found a new nest. Almost always the old colony will have died out, and if the site is free of parasites one of the new queens will return and reuse that site.Newly emerged workers start out at the bottom of the dominance hierarchy in the social colony. As they age, they move closer to the position of queen. Queen-side workers are often egg layers and interact more frequently with the queen. This social position may pay off later, after the competition point is reached. When the queen is overthrown by the aggression of the workers, the most dominant worker will have the best likelihood of contributing more eggs to the colony brood and will perhaps climb to the position of “false queen.” The queen appears to maintain a constant distance of social dominance from her workers at all points in the cycle, suggesting that she is displaced by the sheer number of workers later in the cycle."B. terrestris" generally forage on a large variety of flower species. Their highest activity is in the morning, with their peak time being noted at around 7-8 am. This is likely because it gets progressively warmer in the afternoon, and foragers prefer ambient temperatures of around 25 °C during nectar and pollen collection.While bees often forage alone, experiments demonstrate that young foragers might learn what flowers provide the most nectar more quickly when foraging with older workers. "B. terrestris" individuals have a faster learning curve for visiting unfamiliar, yet rewarding flowers, when they can see a conspecific foraging on the same species. The discovery of this type of associative learning is a novel insight into bee behavior and may supplement learning via color reward association.

Habitat

"B. terrestris" is most commonly found throughout Europe and generally occupies temperate climates. Because it can survive in a wide variety of habitats, there are populations in the Near East, the Mediterranean Islands, and Northern Africa as well. Additionally, it has escaped captivity after being introduced as a greenhouse pollinator in countries where it is not native, so this bee is now considered an invasive species in many of these places, including Japan, Chile, Argentina, and Tasmania. Nests are usually found underground, such as in abandoned rodent dens. Colonies form comb-like nest structures with egg cells each containing several eggs. The queen will lay egg cells on top of one another. Colonies produce between 300 and 400 bees on average, with a large variation in the number of workers.In temperate areas, variable climates and environmental conditions occur during changing seasons. Lack of available food due to these unpredictable circumstances can often negatively affect colony growth, reproduction, and resistance to parasites. In poor environments with limited food, the few workers born are smaller than average. However, it appears that "B. terrestris" is well adapted to a changing environment, considering colony growth is higher under variable feeding conditions than under stable feeding conditions. Workers and reproductives are also heavier with a variable food supply when compared to stable food availability. This might indicate an adaptive strategy of increased provisioning to save for days it is hard to find food.

Food

Individuals who return from the nest after a foraging run often recruit other bees in the colony to leave the nest and search for food. In "B. terrestris", successful foragers will return to the nest and run around frantically and without a measurable pattern, unlike the ritualized dance of the honeybee. Although the mechanism by which this recruitment strategy functions is unclear, it is hypothesized that running around likely spreads a pheromone that encourages other bees to exit and forage by indicating the location and odor of food nearby. Colonies with lower food stores will often be more responsive to this foraging pheromone. Conversely, in colonies with ample food reserves bees will be less responsive to these pheromones likely to save time and energy from unnecessary foraging.

Predators

Deformed wing virus is normally a honey bee pathogen that results in reduced and crumpled wings, making those individuals inviable. This virus is thought to have spread to "B. terrestris," and in 2004, as many as 10% of queen bees bred commercially in Europe were found dead with deformed wings. This was confirmed as DWV when "B. terrestris" colonies tested positive for the presence of DWV RNA. This could indicate that DWV is a broad range pathogen among bees, or perhaps it has recently been infecting new hosts after transmission from honey bees.