Host‐plant finding and recognition by visual and olfactory floral cues in an oligolectic bee

Abstract

Summary1. Bees use floral cues, such as odour, colour, size and shape, to discriminate and recognize flowers. The interplay between visual and olfactory cues in social as well as in solitary bee species is poorly understood. 2. In this study we tested the host finding and recognition behaviour in a specialized (oligolectic) bee species, Hoplitis adunca (Megachilidae), which collects pollen exclusively on flowers of Echium (Boraginaceae) species. We determined the importance of visual (especially floral colour) and olfactory cues of Echium vulgare flowers in host-plant finding and recognition, as well as in the discrimination of non-host plants (Anchusa officinalis), by foraging-naı¨ve and -experienced H. adunca females. 3. Our investigations showed that the interplay between visual and olfactory cues of E. vulgare flowers is essential for host-plant finding and recognition by H. adunca females. The finding suggests that the blue colour of the flowers attracts the bees, while the olfactory cues, which are Echium-specific, are used by the bees to recognize their host plant and discriminate it from non-host plants. 4. Our results show that different modalities of floral cues need to be studied in a combined approach in order to understand the communication in bee-flower interactions and the cues used by bees to find and recognize their host-plants.

Can Pollen Headspace Volatiles and Pollenkitt Lipids Serve as Reliable Chemical Cues for Bee Pollinators?

“…Volatile cues are considered to improve the adoption of search images and thus accelerate location and screening of appropriate food sources already from long distance [22], and to signal rewarding pollen or nectar sources at short distance [23]. Variability in the ratio of headspace components from both pollen and flowerheads of C. rapunculoides found in the present study does not necessarily rule out that volatiles, either a single compound or a blend, from this plant species contribute to host location and recognition [1]. A certain variability in the ratio of plant headspace constituents can be tolerated by female insects without impeding the function of these blends in host recognition [24] [25].…”

“…-Whereas visual cues in conjunction with volatile cues prompt bees to approach flowers [1], these cues may be insufficient for reliable host recognition. In flowers of Ranunculaceae, Campanulaceae, and other plant families, where pollen is exposed and easily available, the final and ultimate host recognition could be gained upon landing, as suggested by our results.…”

“…The first step is the airborne location and recognition, in which whole-flower volatile fragrances are available for the decision on approaching and landing [1]. The second step is considered to take place upon landing on a host flower, when pollen-originating volatiles and contact chemicals become available, allowing for the final identification of…”

“…-Chemical cues from flowers are involved in bee pollinatorÀflower interactions; together with the predominant visual cues that originate particularly from flower colors, they contribute to proper host location [1 -4]. Volatiles function as a supplement to vision rather than as stand-alone attractants for flower-searching bees [1] [4], whereas they are principal cues for other insect pollinators [5 -7]. Floral chemical compounds potentially carry additional information for foraging pollinators, namely information about pollen load, and, hence, they may increase searching accuracy.…”

“…Generally, volatile cues are reckoned to function as a supplement to visual appearance of host flowers, allowing multisensory orientation of the bee prior to landing on the flower [1] [2] [4]. Volatile cues are considered to improve the adoption of search images and thus accelerate location and screening of appropriate food sources already from long distance [22], and to signal rewarding pollen or nectar sources at short distance [23].…”