Floral nectar and insect flower handling time change over the flowering season: Results from an exploratory study

In recent decades, hundreds of secondary metabolites have been found in floral nectar and many studies have demonstrated that they can play various roles in modulating the behaviour of floral visitors. However, temporal variations in nectar chemistry over extended flowering seasons have never been substantiated. Moreover, the effects of nectar chemicals on insect behaviour are often studied under laboratory conditions, focusing on few insect species under artificial conditions which may influence insect responses. The aim of this exploratory study was to compare nectar chemistry and the durations of pollinator visits in the early and late summer periods of the long-flowering species Echium vulgare L. in natural populations. Nectar samples were collected in the early and late summer periods and insects were observed for a total of 480 min. The biogenic amine octopamine, sugars and the protein to non-protein amino acid ratio increased as the season proceeded. It remains to clarify whether these changes are determined by biotic and abiotic factors or whether the plant expresses some chemical constraint, however it seems likely that changes in nectar chemistry may be the cause of the longer visits by bumblebees to single flowers at the end of the flowering season. Though not conclusive, these results set a baseline for future research and highlight an interesting question. Since long-flowering plants see changing contexts during their bloom period, do they express chemical constraints to regulate their attractiveness?