Effects of hillside aspect, landscape features, and kleptoparasitism on the reproductive success of the solitary bee Osmia caerulescens

1. Osmia caerulescens is a generalist solitary bee well-adapted to altered anthropogenic environments, and the kleptoparasitic wasp Sapyga quinquepunctata has been cited among its natural enemies. 2. We analysed offspring characteristics of O. caerulescens and S. quinquepunctata, at population and individual levels, and compared these characteristics between sunny and shady aspects and between two zones within the valley that differed in landscape complexity (simple and complex zones). 3. The offspring production of O. caerulescens was higher in sunny aspect at population and individual levels while S. quinquepunctata was positively associated with the zone with a lower proportion of agricultural land (complex zone). We did not detect a relationship between number of brood cells parasitised and number of brood cells established by host. Despite the parasitism being higher in the area with favourable characteristics for both species, the reproductive success of O. caerulescens did not show signs of reduction. At the individual level, nests with fewer brood cells were more likely to be parasitised. 4. Studying the relationship of environmental factors and landscape features at population and individual levels provides a better understanding of how these characteristics could be driving the offspring production of the solitary bee and their ecological interactions.