Solitary bees as pollinators

Besides the wind, insects are the main pollinating agents and many of them are hymenopterans. However, among the 20,000 species of bees (Superfamily Apoidea), only a very restricted group has been domesticated for commercial crop pollination, including social and solitary species. The honey bee Apis mellifera L. has been the first domesticated pollinator species, anyway, many cultivated crops benefit largely from the activity of other pollinators, especially when honey bees cannot provide a sufficient pollination service. This occurrence is particularly frequent in crops blooming in early spring or in crops with flowers not enough attractive to honey bees, i.e. because of low nectar and pollen production or for particular flower shapes. In addition to these ecological aspects, which are the result of a long history of coevolution between insects and flowers, modern agriculture and the well-known difficulties that honey bees are suffering of, create new concern that a general decline in the native pollinator populations will have unavoidable consequences on crop production due to insufficient pollination service. The most striking contradiction of the “industrial” extensive monocultures is that on one side they put in forth the need of enormous number of pollinators to satisfy the vast number of flowers contemporarily ready to be pollinated; on the other side, they cancel from the agroecosystem uncultivated meadows, edges and forests, which serve as refuge and conservation areas. The immediate repercussion on pollinating insects is the lack of continuity in blooms: on large areas, flowers are extremely abundant during the short blooming period of the main crops and nearly almost absent in the remaining part of their reproductive season (what is called “green desert”). In addition, very often a dramatic reduction of adequate nesting sites and materials may strongly limit the reproductive success, while, up today, the knowledge about the acute and chronic effects of pesticides on native bees is still insufficient.