Bionomics of five wood-nesting solitary species of bees (Hym., Megachilidae), with emphasis on flower relationships

A detailed description and comparison was done on the bionomics of five species of wood-nesting bees: Chelostoma maxillosum (L.), C. rapunculi Lep., C. campanularum (K.), Heriades truncorum (L.), and Osmia tuberculata Nyl. The diurnal flight activity was best explained by separate temperature and light thresholds. The temperature thresholds of the different species ranged from 16.5 to 19°C. The available nest cavities were divided among the species mainly according to their size, partly according to the sun-shade gradient. The nest structure and the activities of the females at the nest entrances were studied in detail. The flowers visited for food were studied mainly by pollen and sugar analyses of the pollen loads and guts. The pollen and nectar presentation of the main food plants was also studied. C. maxillosum is an oligolege of Ranunculus. C. campanularum and C. rapunculi are both oligoleges of Campanula, but do not compete for nest cavities, which are the most limiting resource. H. truncorum is widely oligolectic and specialized to the family Compositae. O. tuberculate is polylectic. The main nectar sources were the same as the main pollen sources, but many other flower species were occasionally visited for nectar. The pollen in the flowers - and therefore also in the pollen loads - was contaminated with foreign pollen by wind and insects. All the species carry pollen loads dry. The bees mostly collected both pollen and nectar on the same foraging trip, but also only pollen or only nectar. The heaviest loads were about 1/4 - 1/3 of the weight of the bee.