Leafy Spurge
Biological Control Agents
1991
1998
Most of the focus of the biological control program in Fremont County has been on leafy spurge. We have been releasing bio-agents on this weed since the late1980’s. Seven species of insects have been released on leafy spurge.
The most successful of these have been the Aphthona beetles, A. nigriscutis and A. lasertosa. By feeding on the tops of the plants during the growing season and the root hairs throughout the winter they have been very effective in greatly reducing the density and vigor of spurge over hundreds of acres in Fremont County. Millions of these flea beetles have been collected and redistributed over the past 15 years.
In 1990 Aphthona nigriscutis was released on heavy infestations of leafy spurge in the Squaw Creek area west of Lander in Fremont County, Wyoming. In 1993 Weed and Pest Control staff started collecting data to assess the impact that the bio-agents were having on the Leafy Spurge at a number of the sites where A. nigriscutis had been released. These study sites were established by Stephen Van Vleet as part of his graduate thesis. The protocols that he set up are still being used. With the exception of 1998 and 1999, the data has been collected every year since.
For more specific information on A. nigriscutis and A. lasertosa, visit Cornell University's Bio-control website here and here.
Two other species of Aphthona beetles have been released in the Lander area, both A. flava and A. cyparissiae have been released and become established but have not had dramatic effects on leafy spurge.
For more specific information on A. flava and A. cyparissiae, visit Cornell University's Bio-control website here and here.
The leafy spurge hawk month, Hyles euphorbiae, is a strong flyer and can be found across the county, but being just a defoliator it has little effect on the spurge plants. Additionally, hawk moth populations generally remain low in an area, due to predation and disease. Thus, H. euphorbiae plays only a minor role in leafy spurge biological control.
For more specific information on Hyles euphorbiae,visit Cornell University's Bio-control website.
A stem borer, Obera erythrocephala, was first released in 1980 then again in 1996 but was not recovered until 2002. It is now well established in the river bottom between Lander and Hudson and will have a negative effect on the spurge as the population grows in these areas.
For more specific information on Obera erythrocephala, visit Cornell University's Bio-control website.
Another introduced insect doing well in the river bottoms is the leafy spurge tip gall midge, Spurgia esulae, which galls the growing tips of the plants, prevents flowering, and stunts the plants. Therefore, flower and, hence, seed production may be reduced at high gall densities. In Fremont County we have been collecting and redistributing Spurgia galls since 1996.
For more specific information on Spurgia esulae, visit Cornell University's Bio-control website.
Off Target Feeding of A. nigriscutis
The biological control agent Aphthona nigriscutis has been established in Fremont County, Wyoming since 1992. Near one release site a mixed stand of Leafy Spurge and a native plant (Euphorbia robusta (Engelm.)) was discovered in 1998. During July of 1999, A. nigriscutiswas observed feeding on both Leafy Spurge and E. robusta. A total of thirty-six E. robusta plants were located and staked on about four acres of land which had a visually estimated Leafy spurge canopy of over 40%. Eighty-eight percent of the E. robusta plants showed feeding damage. By August of 2001, the Leafy Spurge canopy had declined to less than 5% and the E. robusta had increased to 450 plants. Only 26 of 450 plants (5.7%) showed any feeding damage. For subsequent years the data followed the same pattern. In 2006, of 598 E. robusta originally marked, 391 could be located and evaluated for feeding damage. Four plants (1.0%) had damage consistent with feeding by A. nigriscutis although no actual feeding was observed. The Leafy spurge ground cover was 2%. For the eight-year period, Leafy spurge canopy was inversely correlated to E. robusta density and positively correlated to A. nigriscutis feeding damage showing that as Leafy spurge density declines so does Aphthona nigriscutis feeding on Euphorbia robusta.
For more information on Bio-control of Leafy Spurge visit:
Biological Control of Leafy Spurge: An Emerging Success Story
Invasive.org- Biological Control of Leafy Spurge
USGS, Northern Prairie Wildlife Research Center - Biological Control of Leafy Spurge