Colour vision in pollinators: Conclusions from two species beyond the Apis mellifera model

Abstract

In the present thesis, composed of four chapters, we studied different aspects of the visual system of two pollinator species: Bombus terrestris (bumblebee) and Macroglossum stellatarum (hummingbird hawkmoth). Some studies have already investigated the visual system, behaviour and cognition of both species at different levels. Yet, much information is missing. In the four chapters of this thesis we studied the behaviour of both species, with differences concerning the sensorial system and the applied methodology. In the first two chapters we investigated the behaviour of Bombus terrestris while performing tasks related with discrimination and detection of artificial flowers. In in the last two chapters we studied basic and fundamental aspects of the visual system of Macroglossum stellatarum: the spectral sensitivity and the colour discrimination capacity. Despite the fact that bumblebees (Bombus terrestris) and honeybees (Apis mellifera) are related species, comparative studies have shown differences in many aspects of their behaviour related with the use of visual information. Flowers are diverse and so is the foraging behaviour of pollinators. These can employ different strategies and modulate their behaviour to select, detect and discriminate the most rewarding flowers. Macroglossum stellatarum has been considered as an important pollinator of many plants in Europe; yet, basic information about its visual system remained unknown until the development of this thesis. The results of the present thesis raise the understanding of the visual systems of two important pollinator species in Europe, the bumblebee (Bombus terrestris) and the diurnal hummingbird hawkmoth (Macroglossum stellatarum). For years, experiments using the honeybee helped to build an understanding of insect vision, but similar information for the vast majority of floral visitors remains unknown. The present thesis shows that the visual capacity of each species is unique. The evolutionary processes that have shaped the sensory ability of floral visitors are unclear, but the importance of behavioural studies in the plant-pollinator context is essential, not only because of the economic value of the pollination service, but also to properly understand the mechanisms linking the plant-pollinator relationship.