SHERIDAN — “It is a pretty common misconception of us — that we just spray chemicals,” Sheridan County Weed and Pest Assistant Supervisor Luke Sander said. “But biological control has always been part of our plan.”

In fact, SCWP uses a large arsenal of tools in the fight against pests and noxious, or invasive, weeds in the county, from grazing herbivores that feast on certain weeds to microscopic bacteria that take up residence in the miniscule digestive tracts of mosquitoes.

Noxious weeds are detrimental in many aspects. They often crowd out native plant species, dominating a landscape, and some are unpalatable or even toxic, to livestock or wildlife. Each county in Wyoming houses a weed and pest department that works to keep noxious weeds and bothersome pests such as mosquitoes in check.

“Leafy spurge is by far the worst weed in Sheridan County,” Sander said. “It covers thousands of acres in the county. It is typically worse on the eastern side of the county and it is one of the more difficult weeds to control.”

While herbicides sprayed by air or on foot or 4-wheeler are often used to control invasive weeds, leafy spurge has a much smaller, but powerful enemy — flea beetles. For several years, SCWP has been releasing two species of flea beetles of the genus Aphthona, into areas of the county with leafy spurge infestations. When released en masse into areas with leafy spurge, the beetles feed on the plants, helping to eradicate them.

“They will feed on the plant, but that is not what provides the most control,” Sander said. “The most control comes from their feeding on the roots. When we release the beetles, they will then breed and lay eggs right on the soil level or just below soil level. The eggs hatch and the larvae burrow in the roots of the plant, killing them from the ground up.”

The beetles are not only effective in controlling or eradicating leafy spurge, they also grow in population and can be harvested repeatedly.  Two or three years after being released on a site, SCWP employees are able to return to the site to collect members of the burgeoning population and release them at other locations.

“You can go back for years and years to collect them and keep spreading them around,” Sander said.

The beetles are not cheap, but they are effective. This year, Sander said SCWP spent $100,000 on flea beetles. That amount bought 1.2 million beetles which were released on 240 sites in the county, on property belonging to more than 50 different landowners. Additionally, Sander and his crew harvested 750,000 more beetles locally.

The beetles are often used in conjunction with other methods and Sander carefully selects the sites where they are released.

“We will often release them in real remote and steep terrain, where it is dangerous and more expensive to spray,” Sander explained. “We also do it in areas where there are lots of trees and brush. Sometimes some of the chemicals can be hard on trees and brush so if we can use the beetles in those areas it is a little more environmentally friendly.”

“We get more requests for these because people find that they work and they like the results of them,” he added.  “A lot of these areas have hundreds of acres of spurge so you have to do a little bit of everything. There is a misconception that leafy spurge can be eradicated. We just try to manage it as best as possible.”

In addition to using beneficial insects to control unwanted plants, Weed and Pest also takes advantage of even smaller soldiers in the battle against unwanted insects.

Sander said in the effort to control mosquitoes, and in turn, the prevalence of West Nile Virus, SCWP contracts the use of planes to fly over portions of the county and spray a bacteria called Bacillus thuringiensis.

Bacillus thuringiensis is a naturally occurring bacterial disease that affects not only mosquitoes, but black flies as well. It works by damaging the intestinal tract of mosquitoes and flies, essentially paralyzing it. This causes the insect to die within days of infection, usually from starvation.

Sander said to measure the efficacy of the bacteria, he samples aquatic areas for mosquito larvae before and after the spraying occurs.

“The week after the spray the larvae count is almost always at zero,” he said.

The effectiveness of the bacteria to control mosquitoes and black flies has led some area residents to question its effect on other insects, particularly beneficial insects. However, Sander emphasized that in addition to being very effective, the bacteria is also very targeted.

“It is very specific,” Sander said. “It does not affect fish or other insects. It will not affect honeybees or other pollinators and there are lots of studies that show that.”

In addition to the range of methods used to control local weeds and pests, Sander said public knowledge about the problem and preventive measures are very beneficial in controlling the spread of invasive species. To help area landowners recognize and deal with problem weeds before they get out of hand, Sander is expanding the Weed and Pest’s website to include photos and educational information about common weeds in our area. It will be available later this year at