“Phytopathology, agricultural entomology and applied biology” – M.Ferrari, E.Marcon, A.Menta; School edagricole - RCS Libri spa
Bumblebees, like bees, collect nectar and pollen to feed offspring. They are among the most important and useful pollinating insects for humans. The Bombus genus includes about 250 species; many are present in Europe (about thirty are present in Italy). Bumblebees are widespread in temperate areas or at high altitudes in warmer areas. However, there are some tropical species. Some rare species (Bombus polaris is Bombus arcticus) are able to withstand very low temperatures and can be found in areas with a very cold climate. They are social insects that live in colonies consisting of a queen, nursing workers for the offspring and foragers for the collection of nectar and pollen. The bumblebees are characterized by a yellow and black striped livery, even if there are some species all black or with orange stripes, they are generally bigger and hairier than common bees.
Bumblebees are social insects that live in small colonies, formed by a few specimens, which do not generally survive the winter. The only specimens that survive the winter are the fertilized females who, after the death of the colony, will look for a sheltered place to spend the rigors of the winter season. In the spring, the fertilized female will wake up from hibernation and immediately look for flowers to refresh and start creating the new colony. Typically these are small cavities in the ground or in trees such as abandoned dens, trunks of hollow trees, cracks between stone walls. The female will build a small wax cell with a characteristic amphora shape in which she will deposit some eggs and which she will fill with food. These first eggs give rise to sterile females who will take care, as workers, of the collection of food for the colony and help the mother in the construction of new cells. From the middle of the summer the first females capable of reproducing appear, these will lay unfertilized eggs which give rise to the males. The males will fertilize the new females born at the end of the summer and who will develop the new colony the following year.
Among the bumblebees there are also cases of social parasitism, in which the parasitic species lays its eggs among those of the host, entrusting parental care to the workers of the host species. (B. barbutellus, B. insularis, B. vestalis).
They form colonies more or less like bees although, unlike the latter, the number of individuals that make up the community is significantly lower, both because bumblebees do not create colonies that last more than one season and because the fertilized female is limited to build a small nest for the beginning of the community, which normally ranges from 50 up to a maximum of 300 of the Bombus terrestris. Although in most cases bumblebees do not keep their nest for more than one season, some tropical species live in their nests for a few years (in this case the communities can become significantly larger).
At the end of the summer, the last generation of bumblebees in a certain nest contains queens who will spend the winter in a safe and temperate place ready to give life to a new colony the following year. The queens normally live a year, it is possible that tropical species are even more long-lived. At the end of summer, the queen of the colony loses the pheromone with which she assigns her superiority to the others, thus fertile individuals are born who lay unfertilized eggs which will then give rise to the breeding males who will fertilize them. Meanwhile, the queen is killed by the workers, who however will die with the arrival of the first colds.
Alpine bumblebee Bombus alpinus L. 1758 (photo http://touch.artsdatabanken.no)
Bumblebee Bombus terrestris L. 1758 (photo http://bem.rssing.com)