Imagine viewing a wetland in northern Illinois (or any other northern US state or southern Canada province), and seeing a vast marsh, a hazy, purple brilliance stretching to the horizon. What a gorgeous view of a spectacular wetland! This is a good thing, right?

Now imagine walking into an Illinois marsh and seeing hundreds of dead plants, foliage stripped bare by feeding insects. Thousands more plants damaged so severely they didn't produce their brilliant purple flowers. This was a bad thing, right?

No, wrong in both cases. Although the sight may indeed be beautiful, the scenario is indeed all wrong. The two major problems are that wetlands should not be monocultures -- vast expanses of a single species of plant (no matter how beautiful)--and they should not be populated with the pretty, purple, exotic plant. And seeing the plants stripped bare at the other site was exactly what we had hoped to see --- biological control in action, because, in this case, the plant is the bad guy and the insect is the good guy.

Via the Erie Canal to the Interstates

Purple loosestrife (Lythrum salicaria) is an erect, non-woody perennial that came to North America from Eurasia in the early 1800s. Seeds of the plant came here in several ways--in the ballast of ships, in the wool of sheep, and as an herb. Many times soil (which contained plant seeds) that was dug near the shipyards was used as ballast. Once the vessel reached its destination, the ballast was dumped overboard near shore, resulting in weed colonization. Seeds that adhered to the wool of large flocks of sheep brought in from Europe for the early North American woolen mills were another source of purple loosestrife. Finally, the plants were brought over by well-intentioned immigrants for their herb gardens and by beekeepers because the flowers are an excellent source of nectar.

By the 1830s, purple loosestrife was so common along the east coast that, in the first edition of A Flora of North America, the authors mistakenly thought it was 'probably native'. By the late 1800s, loosestrife had spread throughout the northeastern United States and southeastern Canada, and its exotic origin was recognized. The weed needed two factors to disperse -- disturbance in native wetland communities and a method of dispersal. In 1817 the construction of the middle section of the Erie canal began, which provided both the disturbance and a dispersal method. By 1840, the spread of loosestrife was closely related to canal traffic moving inland from the northeast shipping areas.

Two public works programs during the 1940s broke down barriers that had prevented the spread of loosestrife into Western states. Under the Federal Reclamation Act of 1902, acreage under irrigation significantly increased. Off-water swales and seepage slopes along ditches were the perfect habitat for loosestrife to gain a foothold. Also, construction of the network of interstates led to later increased spread. Specifications for interstates called for well-drained crowns, creating major disturbances. Superhighways cut through previously blocking barriers (such as mountain ranges) and offered opportunities for weeds to colonize new areas.

"Stunning in Leaf and Flower, and Grows Just About Everywhere"

Characteristics that make the plant a formidable invader -- hardiness, tolerance of many moisture and nutrient regimes, and virtual freedom from insect pests and disease -- also have made this plant an attractive garden perennial. Southern Living magazine stated, "Loosestrife is a perennial every garden needs. It's stunning in leaf and flower, and grows just about everywhere."

Purple loosestrife is a broad-leafed perennial that can range in height up to 8 feet. The leaves are long and narrow and are usually opposite, but may also be in whorls of three and four. Its angular stems become woody with age and persist through the winter. The plant has a spike of six-petaled purple flowers. The plants bloom from July to September and seed set begins by mid-July. Seeds are shed throughout the winter. Each seed capsule averages 90 seeds, each approximately the size of ground pepper. With a 1000 capsules per stem and 30 stems per plant, a single plant can produce over 2 million seeds! The lightweight seeds can be transported by the wind, but they usually dispersed by flowing water or by adhering to the fur, feathers, or feet of animals and birds.

Although spread of loosestrife is usually by seed dispersal, vegetative reproduction also occurs in areas of disturbance. Once the crown has reached maximum size, stem and root pieces can produce adventitious roots and begin to move about. Because mature plants can tolerate a range of water levels, soil types, and a broad range of climate, making this a plant that does indeed "grow just about anywhere".

Limited Control Methods -- The Case for Biological Control

Vast stands of loosestrife defy most control efforts. Hand picking is recommended as the first line of defense, but this method works only in the very smallest stands. Burning simply annoys the plant. Above-ground stems and foliage die every winter anyway, leaving intact root crowns. Burning in late winter only burns those parts that are already dead, serving no purpose. Flooding may kill the plant in some cases, but not all. Many sites are filled with loosestrife in standing water. In addition, flooding may kill the very native plants that are already threatened. Although there are available herbicides, applying those herbicides by hand is impractical and costly, and aerial application kills the same native plants that are already threatened by loosestrife. That's why biological control has been welcomed -- it's the only alternative in this case.

Research by the US Fish and Wildlife Service (USFWS) and Cornell University in the 1980's identified several natural enemies of this difficult-to-control weed. Five species of beetles were selected as the most promising and most host-specific, and have been introduced from Europe, through quarantine into the US for research, rearing and release. Two species, Galerucella calmariensis and G. pusilla have been released in large numbers in a number of states and Canada. Eggs of a root-feeding weevil, Hylobius transversovittatus, have been distributed in small numbers to several states. Finally, two flower-feeding weevils have been identified, one of which (Nanophyes marmoratus) has been imported into the US and has had limited distribution.

The biology of the Galerucella species is the best understood. Adult beetles emerge from overwintering conditions about mid-May in Illinois (depending on spring conditions), and begin feeding, showing characteristic "shot-hole" feeding damage. Oviposition begins soon and eggs and beetle larvae are seen beginning in June. Eggs often are laid in the leaf axils; after hatching, first-instar larvae often feed in the meristem. This feeding can damage the growing tip, preventing growth, flowering and, therefore, production of seeds. Later-instar larvae feed on the leaves, skeletonizing the leaves. Full grown larvae then move down the plant stems to pupate below the plant. New adults emerge in late summer, feed and prepare for diapause. One generation per year is the norm, though a partial second generation may be seen.

Biological Control of Purple Loosestrife in Illinois

Although biological control of purple loosestrife is being implemented in many states and provinces, the case history presented will discuss the project in Illinois. A coalition of county and state agencies in Illinois first purchased approximately 7,000 adult Galerucella beetles (both species) in summer, 1994. These were released into field cages at seven sites in five counties in northern Illinois, approximately 1,000 per site. Little was seen of the beetles, which later was understood to be due to the adult beetles going into diapause.

In the winter of 1994-95, this coalition contacted entomologists at the Illinois Natural History Survey for help. Although the state and county land managers had responsibility for, and jurisdiction over, their respective sites, they lacked an understanding of biological control or the facilities to rear more biological-control agents. This expanded partnership led to development of a multi-year plan to rear and distribute insects to sites throughout northern Illinois.

At the Natural History Survey, large-scale production of the Galerucella beetles began in late 1995, aiming for widespread distribution in 1996. Hundreds of roots were dug and transported to the greenhouse for culturing. Individual root crowns were potted, plants caged in wire tomato cages and covered with mesh bags. The quick-growing plants were inoculated with 20-30 adult Galerucella and left for about a month, under 16-hour photoperiod and temperatures of about 25-30 C. At that point, plant foliage had been stripped and new adults were emerging. Beetles were collected daily and readied for shipment (or delivery) to sites in northern Illinois.

Releases in 1996 and 1997, by county, are shown in the accompanying table. Information about the individual release sites can be accessed at the Natural History Survey's Purple Loosestrife Web Site -- http://www.inhs.uiuc.edu/cbd/loosestrife/bcpl.html. A total of 167,000 adult Galerucella were released at 32 sites in 6 counties during 1996, and another 396,000 adults released at 49 sites in nine counties in 1997. As the project matured, collaborators in the counties gained experience and confidence in their ability to make releases and monitor sites. In 1996, all beetles were delivered to collaborators and releases made with both Survey and County staff. In 1997, virtually all beetles were shipped to collaborators, who made the releases.

Because of the increased confidence of county and state collaborators, and the desire to move production to the counties, we implemented a program of on-site rearing in 1997. Collaborators dug and potted loosestrife roots and placed the pots into children's wading pools. When plants were about 2 ft tall, we delivered the beetles and inoculated the plants. These plants remained outdoors, under ambient conditions. When foliage was stripped and new adults were noted, the pots were moved to nearby wetlands and the screen cages removed, liberating beetles to disperse. A total of 187 cages were used for on-site rearing in 1997, demonstrating to collaborators that they were capable of producing beetles for their own distribution and use in education programs.

Signs of Impact
Hosah Prairie -- Lake County

Although other sites in North America were seeing signs of impact by 1995, little damage was seen in Illinois by then. In 1996, quantitative sampling at Hosah Prairie, one of the initial release sites, showed initial signs of promise. This site, just inland from Lake Michigan in northeast Lake County, had a number of discrete, small (5-10 m diameter) sand pools, which held water and large numbers of loosestrife plants. Further inland, large stands of loosestrife could be found. Within three of these pools, a few hundred Galerucella calmariensis were released into field cages in 1994. In late 1996, we found the three original release points, and sampled 100 plants within a 2-m radius around each release point. The plants were classified into one of three categories: 1) damaged, in which the meristem had been fed on, no lateral regrowth occurred, with no flowering; 2) partially damaged, in which meristem damage had occurred, but lateral regrowth had led to some flowering, though reduced; and 3) undamaged, in which no severe damage was seen (but some leaf feeding may have been noted), and full flowering occurred. In 1996, approximately one-third of the 300 plants fell into each category, which was a sign of some initial impact, as no plants were damaged before the 1994 releases.

In 1997, we returned to sample the same site, using the same release points as the center of the sampling radii. In the 1997 samples, only 3% of plants were undamaged, 67% were completely damaged, and approximately 30% had partial damage with recovery. Although there was no large-scale plant devastation (see below -- Savanna), the feeding of plants had reduced loosestrife to a "background" plant, with little or no impact on native species. This site will be monitored again the next few years to see if the reduction of loosestrife -- and rebound of native plants -- continues.

Savanna Railroad Yard -- Carroll County

At the northwest corner of Illinois, along the Mississippi River, came a different sign of impact. This location received 1,000 Galerucella pusilla in 1994, which were released into field cages in three discrete sites, all within about 500 m of each other. Additional beetles were released into nearby sites in 1996 and 1997. In late July 1997, Ed Anderson, a regional biologist with the Illinois Department of Natural Resources, received a shipment of Galerucella from the Natural History Survey and went to release them. As he later recounted in a letter to the Survey, he did not release these beetles at the earlier release sites, because "there were so many dead plants, he didn't think the beetles would have enough to feed on." This was the first sign of true impact on the plants, the kind of impact being seen at other sites around North America.

When we went to check on the site in early August, there was extreme devastation of the plants at all three release sites. At one site, which was along the edge of a shallow pool about 150 m long, dead plants were found all along one edge of the pool, up to 150 m from the release point. Both other release sites were in standing water -- one site was knee-deep. The sight at both of these release points was like a bull's-eye -- a circle of brown, dead plants, 15-30 m in diameter, surrounded by green, unflowering plants, which then were surrounded by purple flowering plants. Larvae covered many of the plants, with a few newly emerging adults. Pupae were seen on duckweed below the stripped plants. A later visit in late August found the plants covered with adult beetles, stripping every last vestige of green. And gratefully, even in the midst of the feeding frenzy, stood untouched -- or just nibbled -- plants of other species, showing us the beetles remained host specific, even in the face of sheer number of beetles and little nearby loosestrife.

Although this site was the only one to date (by late 1997) with severe impact -- and strikingly different from the "reduced flowering" at Hosah Prairie, there are hopes that this sight will be seen again and again, as a few years transpire at the 50-odd other sites. One aspect points to this promise. Ed Anderson noted in 1996 that, although he didn't look closely at the plants where the damage was seen in 1997, it seemed that the plants "didn't flower as much." This same comment has been received from collaborators at several of the other sites in the other counties.

The Future of Purple Loosestrife in Illinois