Leafy spurge has long posed a stubborn challenge for ranchers and land managers across North America. Its persistence has prompted researchers to look beyond conventional herbicides and mechanical removal for ways to bring infestations under control. Because of its extensive underground root system, the Eurasian perennial weed can spread rapidly across rangelands and is difficult to suppress.
In North Dakota, insects were released against leafy spurge in the 1980s. The result offered an early demonstration of how biological control, using an insect that naturally attacks the weed, could substantially reduce an established infestation. repeated large-scale spraying is cost-prohibitive While chemical herbicides are effective. This was among the factors that led to the development of biological control, involving the introduction of natural enemies that could suppress invasive species. The beetles’ impact extended beyond the feeding damage caused by adults. Adult Aphthona beetles feed on leafy spurge foliage, while their larvae attack the plant below ground after hatching. They feed on fine roots and root-crown tissue, weakening the perennial weed and reducing its ability to recover and produce new growth. This combination of above- and below-ground feeding can put sustained pressure on leafy spurge populations.
Department of Agriculture’s Agricultural Research Service , scientists in 1988 released 88 flea beetles near Valley City, North Dakota, as part of an effort to control leafy spurge. At the study site, the agency reported that leafy spurge stem density fell from about 182 stems per square yard to five by 1994. In 1988, a mixed population of the flea beetles Aphthona czwalinae and Aphthona lacertosa was released near Valley City, with A. lacertosa making up more than 90% of the population by 1995.
According to the U.S.
At the North Dakota study site, the effect became particularly dramatic over several years. Researchers at North Dakota State University documented large declines in leafy spurge foliar cover and stem density over several years as Aphthona populations expanded. The black flea beetles spread beyond their original release areas, showing that successful establishment could drive suppression well away from the first release points. Foliar cover also declined substantially. The findings showed that the insects could become established and substantially reduce leafy spurge under favorable conditions. Researchers found that black flea beetle populations persisted even when leafy spurge became scarce, suggesting that the insects could remain in an area after suppressing the weed. However, their impact varied considerably among sites, with soil texture and local conditions influencing the strength of control. The Valley City experiment eventually became more than a local weed-control project. As the flea beetles established themselves, land managers began collecting and moving them to other areas where leafy spurge had taken hold. Hundreds of millions of the insects were eventually collected and redistributed across North America from the Valley City area. The beetles were later incorporated into broader efforts to manage leafy spurge. USDA scientists combined flea beetles with sheep grazing, allowing the animals to consume the weed’s above-ground growth while beetle larvae fed on its roots.
Scientists estimated 182 leafy spurge stems per square yard before the beetles were released. By 1994, the density had dropped nearly 40-fold, to five stems per square yard. A later study published in Biological Control followed flea beetles and leafy spurge at three sites in east-central North Dakota from 1998 to 2006. At a 640-acre demonstration site in Sentinel Butte, North Dakota, the combination reduced leafy spurge enough for native grasses to begin returning.
