Increasing attention has been focused on biodiversity in recent years, based on a number of arguments to justify the conservation of the world's flora and fauna. Such arguments may be economic - that species may have potential for food or medicine - or ecological - that the extinction of any species affects the overall ecological balance. Little attention, however, has been focused on which groups have the greatest impact on maintaining diversity. Hymenoptera is one of these groups. It not only forms a major component of diversity itself, but is vital in sustaining diversity in other groups. Hymenoptera species (bees, wasps, ants and sawflies) are major plant pollinators, seed dispersers and parasitoids and predators of other arthropods (and hence important in biological control). This volume therefore tackles an important subject and concentrates on three key issues: how species of Hymenoptera affect diversity in other organisms; whether Hymenoptera is a group prone to extinction; and the consequences if Hymenoptera species are differentially removed from terrestrial ecosystems. The book is essential reading for entomologists and those concerned with biodiversity and conservation.