Biological invasions are slow-motion disasters. They start small: a few insects hitchhiking on some imported nursery stock, a few seeds escaping from somebody's backyard and taking root in a ditch, a field, or a woodlot. The spread is slow at first. Small populations, even if they are very fecund, can produce only small numbers of seeds or young. Sometimes the invading species spends decades as a small, inoffensive part of the biota before suddenly becoming a major pest. It could be that the shift to pest status is the consequence of a genetic mutation that alters the behavior or ecological tolerances of a species, enabling it to push aside competitors and spread quickly onto new ground.
Purple loosestrife may have made that kind of genetic shift. This European wetland plant has been in North America for nearly 200 years and perhaps longer. It was well represented in botanical collections in the eastern United States by 1830, but it showed no sign of becoming troublesome until a century later. The first hint of difficulty was in southern Canada, where loosestrife began to invade pastures, forming dense monotypic stands. It had spread to the midwest by the 40s, and by the mid-80s only three states in the lower 48--Arizona, New Mexico, and Montana--were free of the plant.
Lythrum salicaria is a wetland species. It can reach a height of six feet on favored sites. Each tall, slender plant is topped by a long spike of brilliant purple flowers that is quite beautiful if you don't know what it signifies. To the knowing eye the spikes look like the floral displays around a coffin. Their beauty makes them creepier than they would be if they were gross and ugly.
The seeds of L. salicaria can be carried by water, by wind, or in mud clinging to the feet of waterfowl. Purple loosestrife stems that break off from a parent plant can take root and grow into vigorous new individuals. Once established in a marsh, purple loosestrife grows so densely that it is difficult for large birds such as ducks to move through a stand.
The native vegetation retreats before the invader. The cattails whose roots support muskrats, the smartweeds whose seeds feed rails, all the bulrushes, arrowheads, cordgrass, wild rice, and other plants of a healthy wetland die out. All the leaf beetles and weevils and butterflies and leafhoppers that depend on those plants disappear too, leaving less food for marsh wrens and leopard frogs. The yellow-headed blackbirds find that loosestrife stems are not strong enough to support their nests, so they leave.
Loosestrife seems to do best in disturbed areas: The Lake Calumet region is a major center of infection in this region. From that base the plant can spread into pristine nature preserves and kill off all sorts of native rarities.
Until quite recently there were only two methods available for fending off purple loosestrife: using herbicides and manipulating water levels. The main herbicide was Rodeo, a chemical approved for application to wetlands. Treatment was difficult and expensive. Each individual plant had to be sprayed, which meant that a person wearing a tank of herbicide on a backpack had to wade through a marsh dousing each stem. If the applicator missed any--and it is a virtual certainty that a few would be missed--the effect of the spraying would be to clear the ground for next year's crop. Altering water depth and the duration of flooding in marshes achieved some success, but it was possible only on sites equipped with water-control structures.
The need for a biological control method was clear, but it was not clear whether such a control existed and not at all clear if anyone had the resources to look for it. Then in 1987 the total budget earmarked for alien plant control by the U.S. Fish and Wildlife Service ($100,000) was granted to the New York Cooperative Wildlife Research Unit at Cornell University for research into purple loosestrife control. We can claim some local credit for this. Local Sierra Club activists led by Donna Hriljac called congressman Sidney Yates's attention to the problem, and Yates, then chairman of the appropriations subcommittee that oversaw the budget for the Department of the Interior, saw to it that the funds were put in the budget.
The search for biological controls involves looking for an organism--often an insect, but other possibilities range from nematodes to fungi--that eats the invading plant but doesn't eat anything else. You start by looking at the plant's native ground, where it has a long evolutionary history--ample time to develop some enemies.
A preliminary survey of European purple loosestrife populations turned up about 100 species of insect that could feed on it. Of these, about a dozen were found only on purple loosestrife plants. Five of these, all beetles, were regarded as sufficiently specialized to undergo further testing. One insect was a weevil whose larva lives in--and eats--the roots of loosestrife. Two were closely related leaf-eating beetles, and the other two were extremely tiny weevils that live in the flowering heads of the plants.
The big question was whether these bugs would continue to specialize in purple loosestrife if they were transported to a new environment. This question was answered at the International Institute for Biological Control in Europe. The idea was to bring North American plants to the beetles rather than risk the release of European beetles in this country. In all, 49 species of plants were tested, using two different kinds of tests. In one test the bugs were given a choice. Caged with a purple loosestrife plant and a plant of another species, they were observed to see if they stayed with the loosestrife or started nibbling on the test plant. In the second test the bugs were locked in with just the test plant. Here the choice was eat this or starve. The successful beetle chose starvation.
The most critical test involved plants that are closely related to the target species. Here in Illinois, Lythrum alatum, winged loosestrife, is a common wetland species. Would the beetles turn to alatum if they got the chance?
The two leaf-eating beetles of the genus Galerucella did nibble lightly on the winged loosestrife. Larvae can develop into adults on the plant, but adults reared on alatum produce only about 5 percent as many eggs as adults reared on salicaria, and few of those eggs survive to adulthood. Galerucella is not likely to be a threat to winged loosestrife.
In 1994 John Schwegman of the Illinois Department of Natural Resources bought some Galerucella insects from Cornell. He organized a cooperative venture with the forest preserve districts of Cook, Lake, Will, Kane, and Du Page counties and the conservation district in McHenry County and began releasing the leaf-eating beetles at selected sites in the summer of 1994. In Cook County the first releases were at Powderhorn Lake, a forest preserve east of Lake Calumet.
There was no evidence of overwintering by those first beetles, so Schwegman approached the Illinois Natural History Survey for help. The survey has the facilities needed to grow large numbers of Galerucella beetles, and large numbers would obviously be needed. In 1995 beetles from the survey were released at Powderhorn. They were placed on purple loosestrife plants, which were then covered for a week with netting to keep the insects on the plants. Again no beetles lived through the winter.
The 1996 strategy called for multiple releases at several sites, a strategy that was possible only because the Natural History Survey was by then able to raise large numbers of beetles. In Cook County releases took place at Powderhorn Lake, LaBagh Woods, Sand Ridge Prairie Natural Preserve, Beaubien Woods, and in a marsh at Lemont and Bluff Roads in the Palos Preserves. The cold spring and high water levels made things difficult, but the beetles persisted, and this spring all five sites showed signs that some beetles had made it through the winter.
By July damage to loosestrife plants was visible at all the sites except LaBagh. Some plants were damaged to the extent that they were not flowering. According to John Wiedenmann of the Natural History Survey, the insects have begun to show signs of their presence at several sites. At Hosah Prairie, near Illinois Beach in Lake County, a survey of 300 plants in 1996 found about one-third not flowering, another one-third with limited flowering, and one-third untouched. A similar survey this year found about 70 percent of the plants did not flower and another 25 percent had only limited flowering. Only 3 percent of the plants were undamaged. An Illinois DNR site near Savanna is showing spectacular changes, with many dead and damaged plants and few flowering individuals.
The Natural History Survey has received a grant from Chicago Wilderness, the consortium of organizations working to preserve biodiversity in this region, to develop a school curriculum about biological control. Students will grow their own beetles and conduct their own experiments on whether they'll eat only loosestrife. The student will work with the counties to assign their beetles to particular release sites. The plan is to introduce the curriculum in 20 schools during the coming school year and expand to 60 next year.
For at least the last 20 years people concerned about wetlands have been watching the advance of purple loosestrife with a mixture of anxiety and despair. Things were getting rapidly worse, and there seemed to be nothing we could do about it. Now we have some hope. In at least a few small sites things seem to be getting better. And we have a practical way to continue the improvement. The chatter of marsh wrens and the whinnying calls of soras may still resound in our marshes.