AUTHOR=Burger Hannah , Joos Nadine , Ayasse Manfred 

TITLE=Floral Cues of Non-host Plants Attract Oligolectic Chelostoma rapunculi Bees

JOURNAL=Frontiers in Ecology and Evolution

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2021.682960

DOI=10.3389/fevo.2021.682960

ISSN=2296-701X

ABSTRACT=<p>Oligolectic bees are highly dependent on the availability of the host plants to which they are specialized. Nevertheless, females of <italic>Chelostoma rapunculi</italic> have recently been monitored occasionally to visit <italic>Malva moschata</italic> and <italic>Geranium sanguineum</italic> flowers, in addition to their well-known <italic>Campanula</italic> spp. hosts. The questions therefore arise which floral cues promote visits to non-host plants. As host-specific floral cues are key attractants for oligolectic bees, we have studied the attractiveness of olfactory and visual cues of the established host <italic>Campanula trachelium</italic> in comparison to the non-host plants <italic>G. sanguineum</italic> and <italic>M. moschata</italic> in behavioral experiments. Chemical and electrophysiological analyses of the floral scent and spectral measurements of floral colors were used to compare and contrast host and non-host plants. The behavioral experiments showed that foraging-naïve bees, in particular, were attracted by olfactory cues of the non-host plants, and that they did not favor the <italic>Campanula</italic> host scent in choice experiments. Many electrophysiologically active floral volatiles were present in common in the studied plants, although each species produced an individual scent profile. Spiroacetals, the key components that enable <italic>C. rapunculi</italic> to recognize <italic>Campanula</italic> hosts, were detected in trace amounts in <italic>Geranium</italic> but could not be proved to occur in <italic>Malva</italic>. The visual floral cues of all species were particularly attractive for foraging-experienced bees. The high attractiveness of <italic>G. sanguineum</italic> and <italic>M. moschata</italic> flowers to <italic>C. rapunculi</italic> bees and the floral traits that are similar to the <italic>Campanula</italic> host plants can be a first step to the beginning of a host expansion or change which, however, rarely occurs in oligolectic bees.</p>