Secondary compounds in nectar may play a decisive role in determining thespectrum of floral visitors on plants. Flowers of the African coral tree Erythrina caffra arevisited mainly by generalist passerine nectarivores, such as weavers and bulbuls. As thenectar of this species tastes very bitter to humans, it was hypothesized that secondarycompounds may repel sunbirds and honeybees which are common in the same habitats yetseldom consume the nectar. We conducted choice tests using fresh nectar and both sucroseand hexose (glucose/fructose) solutions of the same concentration as the nectar. WhitebelliedSunbirds (Cinnyris talatala) were repelled by nectar of both E. caffra and a relatedspecies Erythrina lysistemon, but Dark-capped Bulbuls (Pycnonotus tricolor) did notdiscriminate between the Erythrina nectar and control sugar solution in terms of amountsconsumed. Honeybees (Apis mellifera scutellata) probed exposed droplets of E. caffranectar and a control sugar solution at the same rate, suggesting that there is no volatiledeterrent, but they immediately withdrew their proboscis far more often from the dropletsof Erythrina nectar than they did from the sugar solution, suggesting that they find Erythrinanectar distasteful. These results contribute to a growing awareness that non-sugarcomponents of nectar can play important functional roles in plant pollination systems.
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