Scientists released 88 beetles to fight an invasive weed—and the results are 'stunning' for our land.

Leafy spurge has long posed a stubborn challenge for ranchers and land managers across North America. The Eurasian perennial weed can spread rapidly across rangelands and is difficult to suppress because of its extensive underground root system. Its persistence has prompted researchers to look beyond conventional herbicides and mechanical removal for ways to bring infestations under control.

According to the U.S. 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. The result offered an early demonstration of how biological control, using an insect that naturally attacks the weed, could substantially reduce an established infestation.

A weed that was difficult to remove

Leafy spurge (Euphorbia esula) is a deep-rooted perennial that can reproduce through both seeds and an extensive underground root system. Its roots can reach considerable depths and contain numerous buds capable of producing new shoots, allowing the plant to recover even after its above-ground growth is damaged. The weed also creates problems for grazing animals. Cattle generally avoid leafy spurge, while its dense growth can reduce the amount of forage available to livestock. North Dakota authorities say the plant's ability to spread through both its roots and seeds makes it particularly difficult to control.

While chemical herbicides are effective, repeated large-scale spraying is cost-prohibitive. This was among the factors that led to the development of biological control, involving the introduction of natural enemies that could suppress invasive species. In North Dakota, insects were released against leafy spurge in the 1980s. 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.

The beetles attacked where the weed was vulnerable

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.

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. 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. Foliar cover also declined substantially.

The findings showed that the insects could become established and substantially reduce leafy spurge under favorable conditions. 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. 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.

From 88 beetles to millions across North America

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. At a 640-acre demonstration site in Sentinel Butte, North Dakota, the combination reduced leafy spurge enough for native grasses to begin returning.

The method does face some challenges. Flea beetles are not effective in all settings; they may be hindered by sandy and wet soils. Biological control does not eliminate an invasive species immediately; it suppresses it to manageable levels. What began with 88 insects near Valley City helped establish a population that could be collected and distributed across much larger areas. For a weed with deep roots, persistent seeds, and few natural enemies in its new range, the solution came from an insect barely bigger than a grain of flaxseed.