The role of colour in insect pattern vision

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A century ago Karl von Frisch advanced our understanding of animal sensory worlds demonstrating in classic experiments that bees see colours. Many insects as most other animals have colour vision and the perception of colour does not require complex higher brain functions. Insects are small-sized and equipped with compound eyes that give blurred views of a spatially complex world. How colourful are these views and how does an insect recognise colourful objects, patterns and shapes in a visual scene? These questions can be well studied in bees, an important insect model system in ecological, behavioural and physiological research. Foraging bees, as other pollinating insects, usually look for particular flowers to efficiently collect nectar and pollen. They will dismiss many other flowers during their search and not approach or land on them. Such flower constancy requires that floral features, e.g. colours, patterns and odours are learned and recognised by bees. This learning ability can be exploited to easily train bees to artificial food sources, as done by von Frisch, where different colours or patterns signal the presence of reward. Using such experimental methods and new tools to measure and quantify colours as they are perceived by bees, I shall investigate how patterns look to a bee if they are colourful, whether and when a bee sees or learns colours independently from patterns. A crucial hypothesis that I will test is whether pattern and colour vision are segregated in the bee visual system, e.g. whether and to which extent pattern vision in insects may be colour-blind, as has been suggested in the past. I shall also look at flowers through bee eyes and brain using optical and sensory models and make predictions of how detectable and disciminable floral colours and patterns are for bees. Detection is the main visual task if a flower is at a large distance and needs to be picked out from the background. In the first set of experiments I will train bees to detect a pattern which are placed on the back wall of one of two Y-maze arms. The other arm is empty. In the maze the bee will have to decide in which arm it sees the pattern. The distance to the pattern determines the size with which it is projected onto the bee eye. As long as the bee can detect a pattern it will enter the correct arm and find a sucrose reward. Moving the pattern further away the detection limit will be reached when the bee will choose both arms randomly. Detection limits will be determined for a variety of two-coloured patterns that consist of a central disc and a surrounding ring or a disc divided in two halfs, resembling the major types of flower displays as seen through the low-resolution eyes of bees. Colours will be varied systematically to understand how colour hue and colour contrast against the background influence pattern detectability. These parameters will be used to analyse colours and patterns in displays of intact wild flowers that I will record using UV-sensitive multispectral imaging. Pattern elements will be also varied in shape and relative size for identifying possible filter mechanisms in the visual system of the bee. In a second set of experiments bees will discriminate between these patterns. Only one pattern will be rewarded. If bees can distinguish them, they will show a clear preference for the rewarded pattern. These results will tell us, how spatial and colour cues in a pattern are perceived by the bee and which ones may be more important in some patterns. Knowing how bees perform pattern detection and discrimination, I will be able to explain how bees see and memorise complex colourful flower displays. The study will provide new insights the bees' perceptual abilities may have influenced the evolution of complex and colourful displays in flowers that aim to advertise themselves effectively to bees and other insect pollinators with excellent colour vision and learning capacity.