Talking of bees we usually think on honeybees. Few people know, however, that there are more than 20.000 species worldwide, which belong to the family of the Apidae. In Austria there are probably more than 650 bee species, among which the Western Honeybee, Bumblebees and solitary bees. There are several common traits that characterise bees. One of which is the fact that they feed themselves as well as their offspring exclusively with vegetable products such as nectar, pollen and occasionally oil. Besides, they are equipped with specialised morphological structures to collect these products (e.g. honey crop, body hair).
Most bees are solitary, which means that each female builds her own nest, lays eggs (10-30) and gathers pollen and nectar for her offspring without the help of members of the same species. Usually, the mother lives 5-11 weeks and dies before her progeny hatches. The latter generally overwinter in their cells as larvae, rarely as pupae or as adult. In temperate zones they hatch between the end of February and August, depending on the species, and start a new life cycle. A few species produce two generations per season. Unlike termites, or the more closely related wasps and ants, there are few social bees. Some species share a common nest or at least a common entrance and sometimes employ a fellow female as a sentry but still care for their own offspring. Others share a common nest and collaborate in nursing activities, but still lay their own eggs. In more complex communities there is a division of labour between egg-laying and nursing sisters of the same generation, but only a few members of the Halictidae, Bumblebees or the Western Honeybee have reached the highest complexity of social behaviour: In such species, individuals of various generations live in colonies and share the task of nursing the brood and maintaining the colony. The offspring descends from a single or a small number of female. Such female may differ morphologically from the rest of the colony. Most colonies in temperate zones exist only for one season. Only a few species form colonies that survive several years.
Bees are ususally warmth-loving insects. They prefer warm and dry habitats. A prerequisite for the occurrence of bees in a certain area are appropriate climatic conditions and the presence of more or less species-specific food plants and nesting facilities. Some species also need material for the construction of their nests. Examples for habitats rich in bee species are dry grassland, forest edges, hedges, naturally regenerating clearcuttings, riparian zones, sand, gravel and clay pits, unclutivated land in towns, small-scaled vineyards, orchards with moderate management of the grassland, waysides with a diverse vegetation and random gardens.
Slightly more than half of the bee species native to central Europe build their nests in more or less vegetated and compact soils or steeps. Just like their close relatives, the sphecoid wasps, they dig small tunnels that may be from a few centimeters up to a meter long. Andrenidae and Halictidae belong to this group. Slightly less than a fifth of the central european species colonise preexisting hollows (e.g. hollow stalks, boreholes and cracks in tree stumps, cracks in dry walls, rocks and posts, cavities and tunnels in the soil, hollow logs and rock caverns). Honeybees, Bumblebees and Mason bees belong to this group. Such species may be kept in nesting aids, such as nesting units, bumblebee-hives or beehives. Only five percent of all native bee species are able to chew tunnels into the pith of stalks (rose, blackberry, mullein or elder) or into dead wood with the aid of their mandibles, where they build their nests. Ceratina or Xylocopa belong to this group of bees. About a quarter of all bee species native to central Europe build no nests at all. They are parasitic and lay their eggs into nests of ususally closely related species, similar to a cockoo. Their larvae then feed on the provisions that have been supplied by the their foster mothers.
For nest-building bees utilize body secretions, foreign materials or a combination of both. Most bee species coat the inner surface of brood cells with water-repellent secretions, produced by the saliva glands in the head an the thorax or by the abdominal Dufour gland. Bumblebees and Honeybees use wax for the construction of brood cells, which is secreted by abdominal glands. All substances are processed with the tongue or with the aid of specialised structures on the abdomen or on the legs. Foreign materials used for coating and separating brood cells, sealing the nest entrance and for the construction of free-standing cells range from body hair, petals, leafs, resins, pith and wood particles to sand, clay or even small stones – virtually everything small enough to be transported by the bees to their nest. The kind of matarial used by bees is species-specific.
Ecological and economic significance
About three quarters of all species of flowering plants and more than 80% of all crop species cultivated in Europe are pollinated by insects. The remaining 20% are mainly pollinated by the wind. In addition to butterflies, beatles and flies, about half of all pollinating insect species belong to the group of Hymenoptera, which among other species comprises bees. The predominating role of bees for pollination does not only result from the high amount of species involved but also from the fact that they are the only group among the insects mentioned above that feed both themselves and their offspring with pollen and nectar. Therefore it is extremely difficult to quantify the overall significance of bees for pollination. What is sure that bees play an important ecological role, which surely exceeds the economic significance of crop pollination. Pollination by bees ensure sexual reproduction of a great number flowering plants and hence the stability of ecosystems. It is not a coincidence that the evolutionary boom of flowering plants, starting more than 100 million years ago, coincided with the evolutionary boom of bees.
Pollination of crops
The vast majority (84%) of all european crop species, of which we know the type of pollination (about two third of all crop species cultivated in Europe), are pollinated by insects. Pollination not only determines crop yield, but also affects quality (size, shape, preservability) of fruits. And even in self-fertilising crop species or varieties, cross pollination may increase yield. Crops are usually cultivated in large monocultures. Under such circumstances, naturally occurring population of pollinators are usually not aboundant enough to assure optimal pollination, creating the necessity to import or artificially propagate pollinators. As a result of traits such as the number of flower visits per unit of time, quality of pollination, some pollinating species are more suitable than others. The challenge lays not only in the implementation of suitable conservation measures for naturally occurring populations of pollinators but also in finding a suitable pollinator for a specific crop species in a certain area.
Honeybees as pollinators
The Western Honeybee (Apis mellifera) makes certainly the biggest contribution towards the pollination of entomophilous crops in Europe due to her enormous population size (up to 50.000 individuals in one colony), her foraging behaviour (information exchange with other foragers of a colony) and foraging stability, her polylectic feeding, her long lasting seasonal activity and her long flying range (about 2 km). Nevertheless, honeybees only fly during good whether. Therefore, in regions with unfavourable wheather conditions, they are less reliable pollinators.
Bumblebees as pollinators
Bumblebees (Bombus sp.) have a shorter seasonal activity but also fly during unfavourable wheather conditions and, in contrast to honeybees, are buzz-pollinators, which is important for members of the nightshade family such as tomatoes, eggplants, pepper and members of the heath familiy, such as bleberry and lingonberry. Since bumblebees have to found a new colony each year, they are, however, less important for pollination in early spring. Since the development of a method that allows bumblebee rearing throughout the year, their significance for crops has, however, increased. They have also turned out to be better pollinators in greenhouses, since they do not attempt to leave the greenhous in order to forage elsewhere. Besides, they are easier got to pollinate plants that do not produce any nectar, such as tomatoes.
Other bees as pollinators
Among the solitary bees, members of the Andrena, Osmia and Athophora family pay an important contribution to the pollination of early flowering fruit plants such as apple and probably members of the fabaceae family. Just as bumblebees they fly during unfavourable wheather conditions, but have a short seasonal activity (3-4 weeks), which is compensated for by the successive activities of different bee species. Some solitary bees are also buzz pollintors.