Tiny but significant: On the importance of thrips as pollinators

BACKGROUND: Thrips (Thysanoptera) are minute plant and flower visitors in ecosystems across the world but are commonly viewed as notorious pests and too small to effect pollination. The role of thrips as pollinators is thus largely neglected. We provide an overview of the number of plant taxa that are pollinated by thrips, the floral traits of thrips-pollinated plants, and discuss why thrips can be effective pollinators.

MAIN FINDINGS: Thrips pollination occurs in almost half of all seed plant orders, 53 families and 102 plant genera. In many taxa, thrips are the primary or only pollinator. Thrips effectiveness as pollen vectors is enhanced by enormous thrips population sizes in inflorescences, pollen loads of up to >100 grains per individual, and the ability to travel in wind streams. A meta-analysis shows that thrips can significantly contribute to seed and fruit set compared with open pollination controls. A review of the floral traits of thrips-pollinated plants suggests that there is no universal "thripophily" pollination syndrome. One plant trait that stands out is a floral architecture that limits access to larger pollinators and gives thrips a refuge, such as globose or disk-like structures with small or slit-like openings. Some specialist systems exhibit characteristic floral or cone odours that attract thrips; however, too few systems have been studied in detail to cast a general description. Together, our results suggest that pollination by thrips is more common than has been historically perceived, and thrips should not be overlooked in pollination studies and as agents of selection of floral traits.