Biological Control of Invasive Plants in Wyoming


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Biological control, or biocontrol, is the use of living organisms to control weeds or pests. These living organisms can be insects, fungi, nematodes, or diseases. Most often insects are the agents used for invasive plant control. Invasive plants are invasive for many reasons. They can have structural or chemical defenses which discourage grazing. They can secrete chemicals from their tissue, known as allelopathy, which can inhibit neighboring plant growth. They were also introduced to a new continent where evolutionary adaptations from thousands of years of coexistence haven’t taken place. This means there are often very few native herbivores which feed on the invasive plant leaving them undamaged and more competitive for resources.

The goal of weed biocontrol is to increase herbivory on these exotic plants releasing the native plant from the exotic plants completive edge. This is done by releasing biocontrol agents, usually insects, into weed populations. It is true, these biocontrol agents themselves are exotic species deliberately introduced to a non-native range. This can also be said about many non-invasive ornamental plants.  

Biocontrol agents are regulated by the USDA, Animal Plant Health Inspection Service and must go through a rigorous scientific evaluation prior to approval of their U.S. introduction. This process takes many years from discovery to release. Agents who attack native species will not make the cut. However, agents which prove to be extremely selective and only seek the weed of concern may be considered for biocontrol release. Most often, successful agents will not completely eradicate their targets population, but instead their population will rise and fall as the targets population rises and falls. This is similar to the predator prey analogy. A classic example is with the Aphthona spp. insects used for leafy spurge management. These insects are very good at controlling leafy spurge. Their populations will rise exponentially when there is a substantial source of leafy spurge, but as the leafy spurge population declines so does the Aphthona beetle.

BIO 2Release of non-indigenous organisms doesn’t come without some level of risk. Wyoming Weed and Pest Districts utilizes biocontrol as part of our integrated management planning. This means we only consider the use of biocontrol insects for weed management of widespread weed populations, populations where other management options are not appropriate, or populations in extremely challenging terrain. The goal of biocontrol is not eradication, but rather to even the playing field. Biocontrol can help maintain biodiversity of ecosystems and some level of their historic structure, function, and services by limiting the dominance of invasive plants.

The Wyoming Biological Control Steering Committee has a strong history of supporting the research and development of potential new biocontrol agents for the state. Current projects supported include the research for potential agents for the control of whitetop, dyer’s woad, russian olive, russian knapweed, yellow and dalmatian toadflax, perennial pepperweed, houndstongue, and oxeye daisy.

For more information about Wyoming biocontrol, please contact your local county Weed and Pest Supervisor (see District directory), or the Chairman of the Wyoming Biological Control Steering Committee, Aaron Foster at 307-332-1052 or This email address is being protected from spambots. You need JavaScript enabled to view it. .

The following list contains biocontrol agents and their target weed which have been utilized in Wyoming.

Target Weed

Bio Control Agent

Canada Thistle

Urophora cardui


Ceutorhynchus litura

Musk Thistle

Trichosirocalus horridus

Dalmatian & Yellow Toadflax

Mecinus janthinus

Field Bindweed

Aceria malherbae

Spotted & Diffuse Knapweeds

Larinus spp.


Bangasternus fausti


Agapeta zoegana


Cyphocleonus achates


Sphenoptera jugoslavica

Leafy Spurge

Aphthona spp.


Spurgia esulae


Oberea erythrocephala

Common Mullein

Gymnetron tetrum

St. Johnswort

Chrysolina spp.


Aplocera plagiata

Russian Knapweed

Jaapiella ivannikovi


Aulacidea acroptilonica


Diorhabda elongata


WYO-BIO Newsletter- Biocontrol News and Views for Wyoming

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