Flower patterns improve foraging efficiency in bumblebees independent of nectary guidance

Colourful patterns on flowers are thought to benefit both pollinators and the plants they visit, by increasing the plants’ pollination success via an improved foraging efficiency of its pollinators. This increased efficiency is thought to result from a guidance effect of the flower patterns, correspondingly termed ‘nectar guides’, which indicate the position of the nectary to visiting pollinators. While it is well established that flower patterns play an important role in flower choice, the mechanisms underlying their function for flower-visiting insects remain poorly understood. In this study, we quantified the contributions of patterns to all phases of flower interaction in the buff-tailed bumblebee ( Bombus terrestris ). We analysed their flight paths, as well as landing positions and walking tracks on artificial flowers with different pattern types. We reveal that flower patterns improved the overall foraging efficiency of the bees by up to 30%, by guiding their approach flight, landing positions, and departure decisions. Surprisingly, these effects were not related to nectary guidance. Since we conducted the experiments with experienced foragers, which represent the majority of insect pollinators active in nature, the newly described nectary-independent guidance effects of flower patterns are of fundamental importance to plant-pollinator interactions under natural conditions.