Knapweed
Guides
Agapeta
Agapeta is a genus of tortricid moths in the subfamily Tortricinae. The genus includes at least four described species, with A. zoegana (the knapweed root-borer moth) being the most extensively studied due to its use as a biological control agent for invasive knapweeds in North America. Larvae are root-feeding specialists, and the genus is native to Eurasia with some species introduced to North America for weed management.
Agapeta zoegana
sulphur knapweed moth, yellow-winged knapweed root moth, knapweed root moth
A small, bright yellow moth native to Eurasia, introduced to North America in the 1980s as a biological control agent for invasive knapweeds (Centaurea maculosa and C. diffusa). The larva is a root miner that tunnels through the root cortex, causing moderate to considerable damage to host plants. Adults are short-lived, with flight activity from May to August. The species has established populations in western North America and is compatible with other knapweed biocontrol agents.
Cyphocleonus achates
knapweed root weevil
Cyphocleonus achates is a Eurasian root-feeding weevil introduced to North America as a classical biological control agent against invasive knapweeds, particularly spotted knapweed (Centaurea maculosa) and diffuse knapweed (C. diffusa). Adults are flightless, large-bodied weevils that feed on foliage, while larvae cause significant damage by mining into root cortex and inducing gall formation. The species has established populations across much of the western United States and is considered one of the most damaging root-feeding insects on knapweed in its native range.
Larinus minutus
lesser knapweed flower weevil
Larinus minutus is a small true weevil used as a biological control agent against invasive knapweeds, particularly diffuse knapweed (Centaurea diffusa) and spotted knapweed (Centaurea maculosa). Native to southern Europe and the Mediterranean, it was first released in the United States in 1991 and is now established throughout the western United States. Adults feed on knapweed foliage and flowers, while larvae develop within flower heads and consume developing seeds, often destroying 100% of seeds in infested heads.
Larinus obtusus
Blunt Knapweed Flower Weevil
Larinus obtusus is a small true weevil in the family Curculionidae, commonly known as the blunt knapweed flower weevil. It is native to Europe and the Middle East and has been introduced to North America as a biological control agent against invasive knapweeds (Centaurea species), particularly spotted knapweed. The species is closely related to Larinus minutus, with which it shares similar morphology and ecological role.
Metzneria paucipunctella
spotted knapweed seed head moth
Metzneria paucipunctella is a gelechiid moth introduced from Europe to North America as a biological control agent against spotted knapweed (Centaurea maculosa). Adults are small, narrow-bodied moths approximately 8 mm long with brownish-gray coloration, light speckling, and large recurved antennae. Females deposit eggs at the base of knapweed flower heads, where larvae burrow inside to feed on developing seeds and florets. Larvae are small white grubs with dark heads that overwinter within seed heads and pupate the following spring. The species has been established across much of the western United States since its introduction in 1980.
Urophora affinis
Knapweed Gall Fly
Urophora affinis is a tephritid fruit fly native to Eurasia that was introduced to North America as a biological control agent for spotted knapweed (Centaurea maculosa) and diffuse knapweed (C. diffusa). The species forms galls in knapweed seed heads, where larvae develop and reduce seed production by up to 95%. First released in Montana in 1973, it has established populations but remains concentrated near release sites with limited dispersal ability. The fly is multivoltine, with adults emerging in June and larvae overwintering in seed heads.