Mimicking female insects to attract male pollinators is an important strategy in sexually
deceptive orchids of the genus Ophrys, and some species possess flowers with conspicuous
labellum patterns. The function of the variation of the patterns remains unresolved, with
suggestions that these enhance pollinator communication. We investigated the possible
function of the labellum pattern in Ophrys heldreichii, an orchid species in which the conspicuous
and complex labellum pattern contrasts with a dark background. The orchid is pollinated
exclusively by males of the solitary bee, Eucera berlandi. Comparisons of labellum
patterns revealed that patterns within inflorescences are more similar than those of other
conspecific plants. Field observations showed that the males approach at a great speed
and directly land on flowers, but after an unsuccessful copulation attempt, bees hover close
and visually scan the labellum pattern for up to a minute. Learning experiments conducted
with honeybees as an accessible model of bee vision demonstrated that labellum patterns
of different plants can be reliably learnt; in contrast, patterns of flowers from the same inflorescence
could not be discriminated. These results support the hypothesis that variable
labellum patterns in O. heldreichii are involved in flower-pollinator communication which
would likely help these plants to avoid geitonogamy.
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