Western Bumble Bee

Western bumble bee workers have three main color variations. The first color variation is found from northern California, north to British Columbia, and east to southwest Saskatchewan and Montana. B. occidentalis in these areas have yellow hair on front part of thorax. They are also marked by black hair segments on the basal section of the fourth abdominal segments have black hair and whitish lower edge of the fourth and fifth abdominal segments. In addition, they also have sparse whitish hairs that may appear black on the sixth abdominal segment, and an entirely black head. The second color variation is found along the central coast in California. It has yellow hair on the sides of the second abdominal segment and all of the third abdominal segment and a reddish-brown hair on fifth abdominal segment. The third color variation is found from the Rocky Mountains to Alaska. It has yellow hair on the thorax behind the wings and on the rear of the second and all of the third abdominal segments.

Identification. All insects have three main body parts; the head, thorax, and abdomen. Bumble bee species identification tends to refer to colorations on the abdominal segments. The abdominal segments are numbered from T1 to T6 (T7 if male) starting from the abdominal segment closest to the thorax and then working ventrally.

Sex determination. …

Bombus occidentalis was once one of the most common bee species in the North West America. They have been found from the Mediterranean California all the way up to the Tundra regions of Alaska, making them one of the bees with the widest range geographic range. However, recently there has been a noticeable decline in population. In the past decade, the population of B. occidentalis has dropped by around 40.32%. The disappearance of these bees have been especially significant in California, western Oregon, and western Washington. The range and persistence of B. occidentalis has also gone down by around 20%. Some scientists point to the rise of Nosema, a parasite, as the reason for the decline in population. Others say that the population decline could have come because of the invasion of European honey bees. A recent study in 2016 suggests that the Western bumble bee population is rebounding, possibly due to evolutionary development of resistance to Nosema.

Western bumble bees are generalist foragers. Because they do not depend on any one flower type, they are considered to be excellent pollinators. Bumble bees are also able to fly in cooler temperatures and lower flight levels than many other bees. Additionally, bumble bees perform "buzz pollination". This behavior is displayed when a bumble bee grabs the pollen-producing structure of the flower in her jaws and vibrates her wing musculature, causing vibrations that dislodge pollen that would have otherwise remained trapped in the flower's anthers. Tomatoes, peppers, and cranberries are some of the plants that require this type of pollination. For these reasons, bumble bees are considered to be more effective pollinators than honey bees. Bombus occidentalis has been commercially reared to pollinate crops such as alfalfa, avocados, apples, cherries, blackberries, cranberries, and blueberries. Workers collect nectar and regurgitate it in the nest. Pollen is collected and put into "pollen baskets" located on the hind legs. Nectar provides carbohydrates while pollen provides protein.

Foraging behavior. B. occidentalis are social bees, and successful foragers returning to the nest can stimulate their nestmates to forage, although presumably like other bumble bees, they cannot communicate the actual location of resources. This phenomenon is often referred to as 'foraging activation'. …