Contribution of thrips to seed production in Habenaria radiata, an orchid morphologically adapted to hawkmoths.

The very high floral diversity of Orchidaceae has often been attributed to the intricate relationships between orchids and their pollinators. In particular, the interaction between long-spurred orchids and hawkmoths has been well-studied. However, several recent studies suggest that pollination is driven by complex factors, including floral syndromes and local pollinator availability. Here, we investigated contributions of thrips to seed production in the presumably hawkmoth-pollinated long-spurred orchid Habenaria radiata, using pollination experiments and floral visitor observations. These experiments and observations showed that H. radiata is pollinated by both hawkmoths and thrips. Thrips intrude into the pollen sac, causing several massulae to be shed onto the stigma of the same flower, which is located just below the pollen sac. The fruit set and seed set of flowers enclosed in mesh bags (which allow thrips in) and in flowers enclosed together with thrips in paper bags, were much higher than in flowers enclosed in paper bags without thrips. This suggests that thrips partially contribute to fruit and seed production in this species. It provides evidence that thrips can contribute to seed production in a long-spurred orchid that is morphologically adapted to lepidopteran visitors. Unlike the compact pollinia of typical orchid species, those of H. radiata are mealy and friable, and thrips can therefore dislodge the pollen grains in small clumps. We suggest that secondary pollination by thrips may be more common than previously recognized in orchids with granular pollinia.