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A SOUTH African daisy offers promises of sex to con male insects into spreading more of its pollen.

Many flowers produce nectar to entice pollinating insects to visit, but only orchids were known to tempt male insects with flowers that resemble females. Now at Stellenbosch University and at the University of KwaZulu-Natal in Pietermaritzburg have shown that Gorteria diffusa daisies use the same sexual lure as some orchids. The petals of this daisy vary widely, with some bearing markings that look uncannily like the bodies of female flies. Ellis and Johnson found that male bombyliid flies tried to copulate avidly with flowers whose petals most resemble female flies, seen in the top row of the photo (right). The middle row elicited a 鈥渟ly inspection glance鈥�, they say, while the bottom row received 鈥渢otal [sexual] disinterest鈥�: males merely fed on their nectar.

Ellis and Johnson also tracked how the flies spread pollen. By replacing it with fluorescent powder, they showed that flowers which elicit the most ardent sexual advances are also most successful at spreading their pollen (). Males move rapidly between flowers looking for mates, so markings resembling a resting female likely boost visits to a flower. What鈥檚 more, amorous males are more active than feeding ones and so spread more pollen.

at the University of Auckland, New Zealand, who studies sexually deceptive orchids, says the finding might provide the missing link between food- and sex-based strategies used by plants to attract pollinators.

鈥淭he study provides intriguing insight into how sexual deception might evolve from the much more common food deceptive system, and how both systems can operate simultaneously,鈥� she says.