Bombus vosnesenskii

Bombus vosnesenskii, the yellow-faced bumblebee, is a species of bumblebee native to the west coast of North America, where it is distributed from British Columbia to Baja California. It is the most abundant species of bee in this range, and can be found in both urban and agricultural areas. Additionally, B. vosnesenskii is utilized as an important pollinator in commercial agriculture, especially for greenhouse tomatoes. Though the species is not currently experiencing population decline, urbanization has affected its nesting densities, and early emergence of the B. vosnesenskii has been implicated in the increasing lack of bee diversity on the West coast. The genus name Bombus – the bumblebee – comes from the Latin word which means a buzzing or humming sound. There are 250 species split into 38 subgenera within the genus Bombus. These subgroups share similar morphologies, despite their varied habitats and behavioral patterns. However, many of the groups are monophyletic based on the distinct genitalia of the male bee. Genetic studies have revealed the bumblebee to be closely related to the sting-less bee and the honey bee. Bombus vosnesenskii falls into the Bombus subgenus Pyrobombus. Bombus subgenera contain two primary morphological categories, short-faced and long-faced. Pyrobombus is included in the short-faced clade. The subgenus Pyrobombus is both monophyletic and the largest of the subgenera. Bombus vosnesenskii has a number of distinctive features. These include short, even hair, the rounded angle of the basitarsus, which is the middle leg, and a square face. Additionally, the fringed hair of its hind legs forms the corbicula, or pollen basket. Queens are between 18 and 21 mm long. Workers are between 8 and 17 mm while males are between 10 and 15 mm. Queens, workers, and males all have medium length antennae and similarly shaped and sized eyes. They are patterned with black and yellow hairs. The queen and the female workers are almost always identical in coloring. They have almost entirely black thoraxes with stripes of yellow at the head and at the T4 segment of their thorax. The male drones mostly look similar to their female counterparts, but in some cases will have more yellow on their sides that extends farther up the back of the thorax. Although historical data for insect distribution is sparse in western North America, it is clear that Bombus vosnesenskii is not experiencing a population decline; it is amongst the most common bee species on the West Coast of the United States, and the most common bumble bee from Oregon northward. The nesting distribution ranges from British Columbia to Baja California. Historically, Bombus occidentalis, the so-called 'western bumble bee' was the most common species, with a distribution all the way from California to British Columbia and Alaska, but diseases introduced by commercial rearing operations in the eastern United States brought B. occidentallis to the brink of extinction, and B. vosnesenskii has filled the gap. B. vosnesenskii's success in the vacuum left by B. occidentalis has not been the perfect story of nature finding balance after disturbance, however; in the San Francisco area, the frequency of B. vosnesenskii appearances to inversely correlate with the species richness of bees in the area, indicating that B. vosnesenskii outcompetes other bee species for space and resources. This may be due to the species' early emergence during the season, allowing it to overtake and monopolize available nest spaces. The bee nests underground, primarily in colony sizes of about 200-300 workers. While it is not currently in population decline, studies have shown that the B. vosnesenskii experiences reduced nesting density in urbanized landscapes. Studies have demonstrated that paved environments in human urban settings have reduced B. vosnesenskii nesting densities. It is likely that this is due to the subterranean nesting habits of this bee species, which is negatively effected by the expansion of impervious substances like pavement.