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Orchid Enigma

Winnipeg Free Press
Sunday August 10, 2003

A blue Cavalier is driving the gravel roads between Stuartburn and Vita, Manitoba. It’s going about five kilometres an hour—dragonflies fly in and out of the open windows, butterflies pass. Inside, University of Manitoba Masters student Christie Borkowsky and her assistant Erin Lubiansky scan the ditches. They are counting the white flower clusters of endangered western prairie fringed orchids.

Manitoba has 35 species of orchids. Some, like delicate fairy slippers, grow under evergreens in the boreal forest. Others, like the western prairie fringed orchid, are plants of the prairie. Southeast Manitoba is the only place in Canada where western prairie fringed orchids grow. Most are found in the 2500-hectare Manitoba Tall Grass Prairie Preserve, a collection of eighth and quarter sections among agricultural fields of pasture, alfalfa, corn and oats. The orchids spill from the preserve into the ditches.

“This is an exceptional, exceptional year,” says Borkowsky. She has worked at the preserve for 10 summers as a field technician and interpreter. She’s seen years when only 1,800 orchids flowered in the whole preserve and in 1997, she counted a record high of 21,000 flowering plants. This year’s count isn’t finalized, but she estimates it will be close to 20,000.

Western prairie fringed orchids are unpredictable. One year they may push up only one, two, or three leaves. The next year they may produce a 30 to 50-centimetre stem spiked with a cluster of up to 28 white blossoms. Then they may be dormant for a year or two, when nothing grows.

“What makes the plant go from two-leaf to flowering—we don’t know,” says Borkowsky. “One theory is that we’ve had excessive moisture last year and this year, and that may stimulate the root system to develop a flower.”

This is definitely a wet year. Borkowsky is out of the car and walking through a sopping field in hikers and socks. Among the big bluestem, sweetgrass and rare whorled loosestrife, the prairie is growing sedges. A yellow rail is calling, a repetitive wooden click. A Le Conte’s sparrow mews. These are species of wet meadows and marsh edges and they are taking advantage of recent wet years.
Borkowsky stops in the middle of a large patch of western prairie fringed orchids. They are so thick—about 650 flowering plants—that they give the impression of being planted, part of a wildflower garden.

Until 1984, botanists didn’t know that the western prairie fringed orchid existed in Manitoba. The orchids only grow in tall grass prairie and, although at one time the most northerly finger of tall grass prairie in North America covered 6,000 square kilometres of southern Manitoba, western prairie fringed orchids are absent from turn of the century survey records.

“It seems almost impossible that anybody doing even a rudimentary survey would have missed those orchids,” says Richard Westwood, Borkowsky’s graduate supervisor and associate professor of biology and environmental studies at the University of Winnipeg. Although the locals knew of the orchids, the scientific community didn’t discover them until 1984 when Karen Johnson, then curator of botany at the Manitoba Museum of Man and Nature, identified the flowere. Says Westwood, “It came as a surprise to everyone.”

Today, the Manitoba Tall Grass Prairie Preserve protects the largest population of western prairie fringed orchids in North America. Because less than one per cent of the province’s original tall grass prairie remains, the orchids are considered susceptible to extinction and are listed as federally and provincially “endangered.”

In one early study, Borkowsky counted how many orchids were pollinated and produced seed each year. She found that, on average, only 2.1 per cent of Manitoba orchids were producing seed, much fewer than the 49 per cent that sometimes make seed in U.S. orchid populations.

The low seed production is worrying. If the plants are producing too few seeds, they may also be producing too few new plants to sustain the population.

One possible cause of low seed production is poor pollination. So, in another study, Borkowsky and Westwood determined how the orchids were pollinated.

Push an index finger into the face of a western prairie fringed orchid, and your fingertip will get stuck. Draw the finger away and the two sticky caps adhering to the fingertip will unsheathe two fleshy stalks capped on the end with pollen-coated knobs. Each is about a half-centimetre long. Orchid pollinia. They look like tiny antennae.

Touch a yellow pollen knob to an orchid’s flat female stigma, right above the opening to the nectar, and it will stick. Pull back and the knob stretches between the sticky caps on the fingertip and the sticky stigma. Finally, the pollen knob releases from the stigma and the pollinium snaps back to the finger. The flower has been pollinated.

To get reasonable levels of pollination, the orchids must attract a pollinator more reliable than a stubby human finger. Borkowsky and Westwood looked for clues in the flower size and shape.

Western prairie fringed orchids are plain white. Their scent is sweet, barely perceptible by day, but pungent by night. The lower petal is a flimsy, frayed lip, unsuitable for supporting a walking insect. These characteristics suggested to Borkowsky and Westwood that the pollinator was a night-flying and hovering insect—probably a moth. And it would be a species that is in the flying adult stage of its life cycle during the orchid bloom in late June to mid-July.

The other two clues hinted at the physical size of the pollinator. The sticky ends of the pollinia are just over half a centimetre apart, so the pollinator must have body parts that can press against the pollinia while it is feeding on nectar. The nectar fills the bulb end of a four and a half centimetre nectar tube that extends behind the flower. So, whatever the pollinator was, it had a long tongue.

The most likely pollinators were one or more of the larger species of sphinx moth. Borkowsky and Westwood set up insect traps around flowering orchids and caught 5,856 night-flying insects. They found orchid pollinia stuck to the eyes of two species of sphinx moth, the Gallium Sphinx and the Wild Cherry Sphinx.

The Wild Cherry Sphinx is the best fit for the orchid: its tongue is close to four centimetres long and the distance between its eyes is five and a half millimetres, an ideal width to pick up the sticky ends of the pollinia.  However, it is uncommon in Manitoba. The Gallium Sphinx moth is just a bit small, and may not be as efficient as the Wild Cherry at pollinating the orchids. Its tongue is only three and a half centimetres long and its eyes are less than five millimetres apart.

Another less-than-ideal situation for orchid pollination is that both of these moths are near the ends of their lives when the orchids bloom. As the orchid bloom period extends into the middle of July, there are fewer and fewer sphinx moth pollinators on the wing.

A combination of low moth abundance and the poor overlap of moth flight period and orchid bloom might be responsible for the low seed production in Manitoba’s western prairie fringed orchids.

In another study, Borkowsky and Westwood tried to improve orchid pollination. They compared seed production in orchid fields lit with black lights to natural fields. Black light attracts moths. They found that orchids in the black light fields produced more seed.

When a seed falls from a plant, it lands on the soil surface. Over time, some seed becomes buried by soil shifted by wind and water and burrowing insects. Many seeds will be stored at soil depths and in locations that are not ideal for germination. This stockpile of ungerminated seed is called the “seed bank.”  Sometimes seeds will lie in the seed bank for years until the soil shifts again, and ideal water, heat and sunlight coax them to germinate. It’s in the seed bank that a plant species saves for the future.

“[Black light] could potentially be a good tool to increase the number of seeds in an area to increase the numbers of orchids,” says Westwood. “More seeds in the seed bank will help ensure the long-term survival of orchids.”

The black light treatment might be especially useful in small, isolated orchid populations that have almost no natural seed production.  For example, some small populations of eastern prairie fringed orchids (often less than 100 plants) in southern Ontario and northeastern U.S. must be pollinated by hand. Instead, researchers might be able to use black lights to attract natural pollinators—saving themselves time and effort and possibly improving pollination.

“With hand pollination, you don’t know if you are pollinating at the right time,” says Borkowsky. “Insects pick up floral cues. They visit when a plant is most receptive to pollination.”

Borkowsky at the Manitobal Tall Grass Prairie Preserve.

Borkowsky is back on the gravel road, bending her knees to squeeze her feet against her boots. Water trickles from her hiking boots. She walks for hours every day and she chooses wet feet over the discomfort of rubber boots.

One of her current research projects is an analysis of the sugar content and volume of nectar, especially determining if the orchids produce more sugar early in the bloom period when moth pollinators are most abundant. In another, she’s tracking how fragrance levels change over time.

“[Borkowsky’s research] is providing excellent baseline information that you need to make decisions about species management,” says Jason Greenall, co-ordinator and ecologist at the Manitoba Conservation Data Centre. “We need to ensure that both the plant and the pollinator are conserved.”