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Biological control agents are organisms such as insects, nematodes, fungi or viruses, that can be used to control and reduce weed populations. They are usually natural enemies of the target weeds, originating from Europe and Asia.

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Agopeta zoegana
(pupa stage)

agopeta moth root feeder - knapweed

Agopeta zoegana
(adult moth stage)


Mecinus janthinus

cyphocleon us knapweed

Cyphocleonus achates

Biological control is suitable for large, dense infestations where other management strategies are neither cost-effective nor environmentally desirable. A good example of such an area in the Thompson-Nicola Region would be knapweed infestations in open grasslands. The agent usually works at weakening the target plant's seed production by feeding on the seed heads, or by eating or inhabiting other parts of the plant (i.e. root systems). Biological control will not generally eliminate the weed problem, and its results are usually seen over time.

The SIWMC has been working for the Thompson Nicola Regional District to offer biological control agents to private landowners within the TNRD free of charge. Biological control is one strategy that is used to combat the spread of some noxious weed species.

How to look for bio agents
Note: insect availability is weather dependent

mogulones crucigar weevil  hound s tongue plant   

Hounds Tongue
(Mogulones cruciger)

• The weevil is approx. 2-3mm long. It is a blackish brown color with a white cross on its back.
• Look for feeding damage on the leaves and at the base of the leaves where they join the stem.
• These weevils are hard to find in person, they drop off the plant and pretend they're dead as soon as they see you coming.
• These weevils are available in May

 mecinus janthinus in dt plant615124349  mecinus beetle615103517  

Dalmation Toadflax
(Mecinus janthinus)

• Look for feeding damage on the stem and foliage of the plant.
• Look for the weevil itself. Black weevil is approx. 3-4mm long.
• These weevils are out in May-June

 larinus on knapweed seed head  larinus minutus615103517  

Spotted/Diffuse Knapweed
(Larinus minutus)

• The Larinus weevil affects the seed head of the plant.
• The Weevil ranges in color from black to brown to green to tan and is approx. 4-5 mm long
• On the old plants, look for a bullet hole in the top of the seed head (that is where the weevil emerged)
• These weevils are available most of the summer, June-August

 cypho615124349  cypho in root615105757  

Spotted/Diffuse Knapweed
(Cyphocleonus achates)

• The Cyphocleonus Achates weevil affects the root of the plant.
• The weevil is approx. 20mm long and is grey and white in color (blends in with the plant)
• In spring and early summer, pull up a root—the larvae will be burrowed down the center of the root system.
• There can be more than one in each root.
• These weevils are available July-August

agapeta in stem61510480 agapeta moth615124346

Spotted/Diffuse Knapweed
(Agapeta zoegana)

• A. zoegana is a small bright yellow moth, 10 mm in length, with brown wing bands.
• The adults may be found resting vertically on the knapweed stems or under the leaves. They have the appearance of dead or dying knapweed leaves.
• In the spring and early summer, look at the root of a knapweed plant—Agapeta girdles the outside of the root system
• The larvae of Agapeta is long and skinny with a brown head.

apthona615103510 apthona on ls plant

Leafy Spurge
(Apthona nigriscutus)

• The Apthona beetles are approximately 3-3.5 mm long and are a shiny brown or brownish with a black dot on their back behind their thorax
• The beetles are out from late July-August


Agents are available in the TNRD for the following  invasive plant species:

Bio agent Typical agent availability*
Diffuse Knapweed
Agapeta zoegana
Cyphocleonus achates
Larinus spp. 
Mid June to late July
Mid June to mid July
 Spotted Knapweed
Agapeta zoegana
Cyphocleonus achates
Larinus spp.
 Mid June to late July
Mid June to mid July
 Leafy Spurge
Apthona cyparissiae
Apthona nigriscutis
Mid June to mid August
Mid June to mid August 
 Dalmation Toadflax
Mecinus janthinus
Rhinusa spp. Mid March to end of May

Mid March to end of May
Mid May to end of June / Mid July to September

Hound's Tongue
Mogulones cruciger

April to end of May / August to mid September

Rhinocyllus conicus
Larinus planus

July to August
Mid June to Mid July

*NOTE: Hound's Tongue and Thistle agents are dependent on agent availability in the Southern Interior Region of British Columbia. Typical availability of adult agents is dependent on the bio agent species and subject to change as a result of seasonal factors.

As a result of the success of the biological control program over the past several years, some of these biological agents are now well established and widespread throughout the Thompson-Nicola Region. For more information about the TNRD's biological control program, or to fill out a request for bio control check out the TNRD's biological control program or contact the SIWMC Coordinator .

If you are currently on our list of candidates for receiving biological control agents, please be sure to keep your personal contact information up to date. Please contact us if any of this information has changed.


lmh27  In 1994, the BC Ministry of Forests and Range published a field guide for biological control agents in British Columbia. This guide is designed to help resource managers in British Columbia identify weeds and select suitable biological control agents for those weeds. Biological control offers stable, long-term solutions to weed problems across the province.

To view and download a PDF version of the Field Guide to the Biological Control of Weeds in British Columbia, click here.