Brood pollination mutualism between cryptic-flower Aspidistra and pollen-parasite midges

Brood pollination mutualisms are obligate interactions in which the specialized insect generally evolves parasitism of its pollinated flower, but whether pollen parasitism could also evolve in nursery pollination systems remains little known. Aspects of pollination, particularly floral phenology and anthesis, as well as feeding habits and life cycles of pollinators, were examined in seven species of Aspidistra (Asparagaceae), in which flowers of most species are cryptic, usually covered by forest litter. The 9-yr field study found that at least six species were pollinated by fungus gnats (Mycetophilidae, Sciaridae) or gall midges (Cecidomyiidae), and their larvae were pollen parasites of the pollinated flowers. As illustrated here, Aspidistra saxicola was exclusively pollinated by a female midge, whose adults fed on pollen and oviposited in flowers, and whose larvae developed in 3-4 d on a diet of the pollen within the corolla. The timing of the midges' life cycle matched the flowering phase of pollen provision for 4-7 d. Unlike previously reported obligate brood pollination mutualisms, in which larvae are seed predators, the sole pollinators, gall midges or fungus gnats, are completely dependent on pollen in multiple species of Aspidistra, illustrating a new fly-pollinated pollen-parasite mutualism in angiosperms.