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SLU Scientists Recognized for Pollination Ecology Research

by Jeanette Grider on 05/01/2018
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Jeanette Grider
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Findings from a multi-year study of slipper orchids by a team of Saint Louis University researchershave appeared in the Botanical Journal of the Linnean Society of London.'

Saint Louis University researchers Retha Edens-Meier, Ph.D., of SLU's Department of Educational Studies, Gerardo Camilo, Ph.D., and Peter Bernhardt, Ph.D., both of the Department of Biology, along with Michael Arduser, a retired entomologist from the Missouri Department of Conservation, recently published the findings of their four-year study of the yellow lady’s slipper orchid.

The yellow lady’s slipper (Cypripedium parviflorum) is an orchid native to North America. Small, isolated populations of this wildflower remain scattered in shady Missouri woodlands and typically bloom from late April to late May. The hollow, shoe-like bottom petal is known as the labellum and that’s what gives the flower its common name. Insects entering the labellum must crawl through this “fun house” to reach the exit holes in the rear. Upon exiting, insects may deposit pollen on the stigma (the receptive female organ). As the insect squeezes through one of the two exit holes, the flower smears its back with sticky yellow pollen.

These flowers offer no edible rewards but look and smell attractive enough to deceive insects into carrying pollen between plants ensuring cross-pollination, which is vital in ensuring ongoing strong and abundant plant life.

Scientists, including noted naturalist and biologist Charles Darwin, have been fascinated for well over a century by the yellow lady’s slipper and have been studying them with great interest, Meier noted.

About the Study

In this pollination ecology study, the researchers wanted to find out whether two varieties of slipper orchids, Cypripedium parviflorum var. pubescens (large size) and var. parviflorum (small size), share pollinators of the same size. Variety pubsecens grows both at Cuivre River State Park (CRSP) and Hawn State Park (HSP) whereas var. parviflorum grows at CRSP but not at HSP.

Researchers measured the flowers at both sites and collected and identified 235 insects, of which 227 were bees (only 11 bees were males), which entered the labella of Cypripedium parviflorum. They found that female halictids were the primary pollen vectors. They found the floral measurements were statistically different between the two varieties but no difference was found between var. pubsecens at the two sites.

Both varieties received insects ranging from less than 4 to more than 10 millimeters (mm) in length. However, the small variety of orchid received more bees in the 4-7 mm range than the larger orchid variety. Researchers also found that more bees in the small (less than 4 mm) and large (more than10 mm) range were captured in the large orchid variety than the smaller orchid variety.

Although there was overlap in bloom time and shared bee species, there was no evidence that the two varieties crossed with each other at Cuivre River. Another exciting discovery was the collection of a novel bee species in a large lady’s slipper at Cuivre River. This was the first time that the bee, Andrena tridens, was recorded in Missouri, although it is found in other states.

In addition, eight bees were identified sheltering within var. pubescens on cold mornings. Although no difference between the ambient temperature and the temperature inside the labellum was found, researchers believe that the labellum may still provide some protection to bees during cool, windy, spring days.

Although only 12 insect species were known previously to carry pollen of yellow lady’s slippers, this study added 84 more, including two species of wasps and a fly. Also, this project could be the first to identify the pollinators of the small variety, var. parviflorum. Nineteen bee species were captured in the small variety and 16 species carried orchid pollen. This information ultimately helps conservationists concerned about the ability of these flowers to reproduce as population sizes dwindle as a result of illegal collections and habitat destruction. Because so much variation exists in flower size in C. parviflorum and because so many taxa of bees are drawn to the orchids, researchers proposed that bee size matters.

While the results of the study provide key information for scholars, researchers and academics, Meier says the findings are also a vital takeaway message for everyone about the relationship of bees, orchids and pollination for a healthy planet.

For media inquiries, contact Jeanette Grider in University Communications at (314) 977-2538 or jeanette.grider@slu.edu.

Photos by Retha Edens-Meier, Ph.D.