Olfactory floral mimicry of injured ants mediates the attraction of kleptoparasitic fly pollinators.

Abstract

Specialized pollination by flies often involves specific floral mimicry of various food and brood substrates.^1,2,3 However, identifying a precise model is challenging due to the ecological diversity of flies, which subject plants to diverse selection pressures.^4,5 Here, I report that Vincetoxicum nakaianum (Apocynaceae) lures kleptoparasitic fly pollinators by producing a floral scent mimicking the volatiles released by injured ants. Field observations confirmed that V. nakaianum is pollinated by four kleptoparasitic chloropid fly species that feed on the body fluids of injured insects.^6,7,8,9,10 In chemical analysis of floral scent, nonane, undecane, octyl acetate (8Ac), decyl acetate (10Ac), and methyl-6-methyl salicylate (6-MMS)^11,12,13 were identified consistently across all samples. A synthetic mixture of these five floral scent components was attractive to pollinating flies. However, in the absence of 10Ac or 6-MMS, the mixture was unattractive to flies. When 10Ac and 6-MMS were offered in combination, flies were attracted; these two compounds alone were, however, not attractive. The compositions of volatiles emitted from injured Formica ants closely resembled V. nakaianum floral scent, sharing 10Ac and 6-MMS. Y-maze experiments confirmed that pollinators were attracted to Formica japonica following spider attack. These results indicate that V. nakaianum employs the olfactory mimicry of injured ants to attract pollinators. Although ants are pervasive and frequently interact with plants, no flowers have been reported to mimic ants. This study highlights the diverse evolutionary outcomes of adaptation to fly pollinators and the evolutionary capacity of ant mimicry in plants.