Orange-belted bumblebee, Tricolored bumblebee
Bombus ternarius, commonly known as the orange-belted bumblebee or tricolored bumblebee, is a yellow, orange and black bumblebee. It is a ground-nesting social insect whose colony cycle lasts only one season, common throughout the northeastern United States and much of Canada. The orange-belted bumblebee forages on Rubus, goldenrods, Vaccinium, and milkweeds found throughout the colony's range. Like many other members of the genus, Bombus ternarius exhibits complex social structure with a reproductive queen caste and a multitude of sister workers with labor such as foraging, nursing, and nest maintenance divided among the subordinates.
Bombus ternarius was first named by Thomas Say in 1837. Bombus is Latin for buzzing, and refers to the sound the insects make. The specific name ternarius refers to the number three, which refers to the bumblebees' three colors.
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TerrestrialTerrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, snails), as compared with aquatic animals, which liv...
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OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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starts withB. ternarius is a small, fairly slender bumblebee. The queen is 17–19 mm (0.67–0.75 in) long and the breadth of the abdomen is 8.5–9 mm (0.33–0.35 in). The workers are 8–13 mm (0.31–0.51 in), and the drones are 9.5–13 mm (0.37–0.51 in) in length. Both the worker and the drone have abdomens about 4.5–5.5 mm (0.18–0.22 in) in breadth.
The queen and workers have black heads, with a few pale yellow hairs. The anterior and posterior thorax and the first and fourth abdominal segments are yellow, abdominal segments 2 to 3 are orange, and the terminal segments are black. The queen and the workers are close in resemblance, and the most striking difference between them is in the size of their fat deposits. Workers have very little fat, particularly in their abdomen, leaving plenty of room for the honey stomach, an enlargement of the oesophagus in which nectar can be stored on foraging trips. In contrast, in young queens, the abdomen is largely full of fat. This leads to queens being heavier for their size than workers.
The drone has a yellow head with a few black hairs. The coloration of the thorax and abdomen is similar to that of the females, with the exception that the last abdominal segments are yellow on the sides. The fur of the drone is longer than that of the females.
B. huntii, another species of bumblebee common throughout the western United States, is nearly identical in coloration to B. ternarius, though it has primarily yellow facial hairs rather than black.
B. ternarius mainly ranges in the northern parts of the US and much of Canada. Their range extends from the Yukon to Newfoundland and Labrador and British Columbia. Their United States territory extends from New York and Pennsylvania to Michigan, Washington, Wyoming, Utah and Montana. The bumblebees are most successful in the northern, temperate climate, but they can rarely be found farther south.
B. ternarius, like most members of its genus, are seasonal, meaning the queen comes out of hibernation in late April to start a new colony. The bumblebee workers fly from May to October when the entire colony dies (except hibernating queens) to start the cycle again.
In late April, the queen comes out of hibernation from under a few inches of loose soil or leaf litter, and begins to search for a nesting site. Bombus ternarius prefer to nest underground in small and shallow cavities like rodent burrows or natural crevices. She flies low to the ground, stopping often to investigate holes in the earth, and once a satisfactory nest site is found, she forages for pollen and nectar to support her future offspring. Next, the queen secretes a protective waxy coating and builds a grove where she lays fertilized eggs destined to be the first of the new workers. The queen straddles the eggs, allowing for close contact between the ventral surface of her abdomen and thorax and the eggs. This close contact allows the queen to incubate her brood with the heat she generates by pulsing contractions in her abdomen.
These eggs progress through four lifecycle stages starting as an egg, then larva, pupa, and after about a month after laying the egg, the adult workers emerge. Considering that the entire lifecycle of a colony is only about a season long, incubation is necessary because it hastens the development of the first workers. However, the generation of such vast amounts of heat is incredibly costly for the queen. The queen uses an estimated 600 mg of sugar per day to incubate her brood. To obtain this amount of energy, she may need to visit as many as 6,000 flowers. Naturally, during her absence, the brood cools rapidly, so the availability of plentiful and rewarding flowers near the nest site is vital.
The newly hatched workers take over the duty of foraging and expanding the nest. The workers also assist in incubation of the eggs and larvae. B. ternarius nests rarely exceed more than 200 individuals.
In late summer, the queen switches to laying unfertilized eggs, which develop into male drones that are meant for reproduction. Towards the end of her life, the queen reverts to laying fertilized eggs. These eggs give rise to new female queens. The new adult queens forage for food. They use the nest for shelter, but the new queens do not contribute to the nests food reserves. During this time, the new queens mate with roaming male drones, build up reserves of body fat, and fill their nectar crop with honey to survive winter hibernation. The rest of the colony, including the old queen, dies in mid-autumn.
Queen and worker bumblebees can sting. Unlike honey bee stingers, a bumblebee's stinger lacks harpoon-like barbs on the end of the stinger, so B. ternarius can sting repeatedly without risk of disemboweling itself and dying. B. ternarius is not normally aggressive, but will sting in defense of its nest or when threatened or provoked.
Major plants visited include Rubus, goldenrods, Vaccinium, and milkweeds. B. ternarius eats and collects both nectar and pollen. The nectar is stored in a special internal pouch called the crop, while pollen collects on the hairs on the bumblebee body. The bumblebee pushes the grains of pollen towards its hind legs, where the pollen is pushed into the pollen basket. At the nest, the contents of the nectar crop is regurgitated, where it is mixed with enzymes and allowed to air dry. As the nectar and enzyme mixture dries, honey is created. Pollen is mixed with the nectar and honey to create a protein-rich larval food.
Before the introduction of western honey bees, bumblebees were the only honey-producing bees in North America; however, only small quantities are produced.
Flight for bumblebees is energy costly. Estimates put bumblebee metabolic rate at extremes surpassing even hummingbird metabolic rates, so efficient foraging and good decision-making is paramount or the workers risk a net loss of energy. Pollen is rich in protein necessary to sustain flight, but is more difficult to collect than nectar. Bumblebees exhibit individual learning. New pollen foragers tend to return lighter from about the first 10 foraging trips, allowing foraging efficiency to increase, until it plateaus at about 30 trips. Furthermore, bumblebees tend to collect pollen when conditions are dry and humidity is lower, presumably because pollen clumps are drier then, making foraging easier. For this reason, more experienced and older workers tend to collect pollen. This approach means inexperienced foragers waste less energy and more pollen is returned to the nest, maximizing the colonies' evolutionary success.
Little is known about its precise foraging range, but bumblebees' range is, on average, up to 6 km (3.7 mi) which can be extended to far away as 20 km (12 mi) when resources are scarce. One would predict that food patches nearest to the nest would be most visited, so would offer the least uncollected nectar and pollen. A trade-off occurs between energy expenditure in flight and the competition between workers. This effect pushes workers to explore further away from the nest to forage. Some propose that bumblebees venture out farther past their nest because foraging near the nest could bring unwanted attention from predators and consequently risk the success of the colony. This predator hypothesis, however, is often dismissed as showing little effect on bumblebee foraging range.
A bumblebees often does not fill its nectar crop to full capacity when foraging. This phenomenon is best explained by the marginal value theorem. The weight of nectar in the nectar crop adds an additional energetic cost to flight, so a heavily loaded bumblebee expends significantly more energy to the point of diminishing returns. Depending on the flight distance, a fully filled crop may cause a bumblebee to burn more energy than a partially filled crop would bring back.
Drones have one function in life: reproduction. They fly in a circuit and deposit a pheromone on prominent places such as tree trunks, rocks, posts, etc., to attract the newly hatched queens. A new queen follows the pheromone trail and mates with the male.
Mating among B. ternarius typically occurs on the ground or in vegetation. The male mounts the female by grabbing her thorax, the queen then extends her stinger and the male inserts his genital capsule. Mating time varies widely from about 10 to 80 minutes, with the sperm being transferred within the first two minutes of copulation. While mating, both the male and female are vulnerable to predators. After the transfer of sperm is complete, the male secretes a sticky substance that hardens into a plug that blocks new sperm for about three days. This prevents other males from impregnating the same queen and competing to fertilize eggs. The plug helps reduce competition and increases the first male's evolutionary success.
Individual colonies have slightly different reproductive strategies. About half of the queens adopt an early switching strategy that produces mostly male drones, and the other half adopt a late switching strategy, giving rise to mostly new queens. Because of this, bumblebee female to male sex ratio differs from the standard Hymenoptera three to one ratio as proposed by the haplodiploidy hypothesis, and sits closer to an even sex ratio. One hypothesis proposes that the reason why bumblebee's sex ratio differ from the characteristic hymenopteran ratio is because of the queen's decision-making. She can decide to adopt an early switching, male-producing strategy, or a late switching, queen-producing strategy. The worker bees have no choice but to go along with the queen's choice. Normally, the workers would work to shift the ratio towards female prevalence, but in the case of B. ternarius, this would disfavor the workers' evolutionary success.
