Variation in nectar quality across 34 grassland plant species.

Floral nectar is considered the most important floral reward for attracting pollinators. It contains large amounts of carbohydrates besides variable concentrations of amino acids and thus represents an important food source for many pollinators. Its nutrient content and composition can, however, strongly vary within and between plant species. The factors driving this variation in nectar quality are still largely unclear. We investigated factors underlying interspecific variation in macronutrient composition of floral nectar in 34 different grassland plant species. Specifically, we tested for correlations between the phylogenetic relatedness and morphology of plants and the carbohydrate (C) and total amino acid (AA) composition and C:AA ratios of nectar. We found that compositions of carbohydrates and (essential) amino acids as well as C:AA ratios in nectar varied significantly within and between plant species. They showed no clear phylogenetic signal. Moreover, variation in carbohydrate composition was related to family-specific structural characteristics and combinations of morphological traits. Plants with nectar-exposing flowers, bowl- or parabolic-shaped flowers, as often found in the Apiaceae and Asteraceae, had nectar with higher proportions of hexoses, indicating a selective pressure to decelerate evaporation by increasing nectar osmolality. Our study suggests that variation in nectar nutrient composition is, among others, affected by family-specific combinations of morphological traits. However, even within species, variation in nectar quality is high. As nectar quality can strongly affect visitation patterns of pollinators and thus pollination success, this intra- and interspecific variation requires more studies to fully elucidate the underlying causes and the consequences for pollinator behaviour.

Critical links between biodiversity and health in wild bee conservation.

Wild bee populations are declining due to human activities, such as land use change, which strongly affect the composition and diversity of available plants and food sources. The chemical composition of food (i.e., nutrition) in turn determines the health, resilience, and fitness of bees. For pollinators, however, the term 'health' is recent and is subject to debate, as is the interaction between nutrition and wild bee health. We define bee health as a multidimensional concept in a novel integrative framework linking bee biological traits (physiology, stoichiometry, and disease) and environmental factors (floral diversity and nutritional landscapes). Linking information on tolerated nutritional niches and health in different bee species will allow us to better predict their distribution and responses to environmental change, and thus support wild pollinator conservation.

Stingless bees use terpenes as olfactory cues to find resin sources.

Insects largely rely on olfactory cues when seeking and judging information on nests, partners, or resources. Bees are known to use volatile compounds-besides visual cues-to find flowers suitable for pollen and nectar collection. Tropical stingless bees additionally collect large amounts of plant resins for nest construction, nest maintenance, nest defense, and to derive chemical constituents for their cuticular profiles. We here demonstrate that stingless bees of Borneo also use olfactory cues to find tree resins. They rely on volatile mono- and sesquiterpenes to locate or recognize known resin sources. Moreover, by modifying resin extracts, we found that stingless bees do not use the entire resin bouquet but relative proportions of several terpenes. In doing so, the bees are able to learn specific tree resin profiles and distinguish between tree species and partly even tree individuals.