Pollination of Prairie Phlox ~ Phlox pilosa

Prairie Phlox ~ Phlox pilosa
The fragrant, pink flowers of prairie phlox are just about finished their display for the season. Prairie phlox is a robust, drought tolerant prairie native that performs best in well-drained soils in full sun.

Use massed on the edges of small prairie plantings or along a sidewalk for a nice effect. The short, upright stature and thin leaves contrast well with larger-leaved prairie perennials such as prairie alumroot which flowers at the same time.

Peck's Skipper Butterfly

Butterlies are the primary pollinator of prairie phlox; they are attracted to the floral fragrance and nectar guides (dark pink marks around the corolla opening).

Nectar is easily accessed by butterflies (and moths) from the disc at the base of the stigma with their long proboscis.

European Skipper Butterfly
taking off from the flower.
Pollen is attached to the proboscis.

As they insert their proboscis into the flowers it comes into contact with the anthers. Pollen attaches to the proboscis and as the butterfly finishes nectaring and moves on to the the next prairie phlox plant, the proboscis coils back into its resting position.

Most of the pollen falls off as the proboscis is coiled, leaving only a small percentage of pollen to be transferred to a receptive stigma on another prairie phlox flower.

Some bumble bee species have tongues long enough to reach the nectar.

An American lady butterfly feeds on nectar.

Hummingbird clearwing moths hover over the flowers and feed on nectar.

Short-tongued bees have no way to reach the nectar in the long tubular flower.

They can however, push their head into the flower opening and reach the anthers near the top of the corolla. The anthers are staggered in the flower corolla, some closer to the top, others out of reach to small bees.

This green sweat bee is feeding on pollen from an anther that was pulled out of the flower tube.

Large and small syrphid (flower) flies land on the tops of the flowers and feed on stray pollen.

Prairie phlox is self-incompatible and therefore requires cross-pollination by insects. In the study by Levin & Berube (1972), the number of pollen grains attached to the proboscis of a visiting butterfly drop by 15% when the proboscis is recoiled, and only 17% of the remaining pollen grains are effectively deposited onto a receptive stigma on another prairie phlox flower visited. Also, only 1% of the pollen that a prairie phlox flower produces is transferred to a stigma on another plant.

Relying on the longer-tongued insects like butterflies and moths to ensure pollination and sexual reproduction of the species is therefore risky as they are so ineffecient at transferring pollen from one prairie phlox plant to another.

References
Hendrix, S. D. (2000). Population size and reproduction in Phlox pilosa. Conservation Biology, 14(1), 304-313.

Levin, D. A., & Berube, D. E. (1972). Phlox and Colias: the efficiency of a pollination system. Evolution, 242-250.