Larinus carlinae

Distinguished from the similar thistle head weevil (Rhinocyllus conicus) by its proportionally longer rostrum (snout). Adults are small beetles with elongated snouts bearing tiny chewing mouthparts at the tip. Body coloration typically blends with host plant foliage. Larvae are white, legless, and C-shaped, found within thistle flower buds.

Associated with thistle-infested areas including agricultural lands, meadows, roadsides, and disturbed habitats where host thistles (particularly Cirsium arvense, Canada thistle) grow.

Native to Europe and western Asia. Introduced to North America: first detected in Maugansville, Maryland in 1971, with establishment likely in the 1960s. Now present across much of the United States and Canada where invasive thistles occur. GBIF records confirm presence in Belgium and Denmark.

Adults emerge in spring when thistle plants begin developing flower buds. Activity continues through the growing season while host plants remain in bud and flower. One generation per year with adults overwintering.

Specialized herbivore feeding on thistles (Asteraceae: Cardueae). Adults feed on developing thistle buds and leaves. Larvae feed exclusively on reproductive tissues within flower buds, consuming developing seeds and floral structures.

• Cirsium arvense - primary hostCanada thistle, main target for biological control
• Carduus acanthoides - hostspiny plumeless thistle
• Cirsium discolor - hostnative thistle, conservation concern
• Cirsium altissimum - hostnative thistle, conservation concern

One-year life cycle. Adults emerge in spring, feed on thistle vegetation, and mate. Females use elongated rostrum to drill holes into developing flower buds and deposit single eggs. Larvae hatch and bore through flower head, consuming reproductive tissues and preventing seed production. Larval development occurs within buds; pupation presumably occurs in soil or within plant material. Adults overwinter.

Adults feed on thistle buds and leaves, causing defoliation and reduced plant vigor. When depositing eggs, females drill precisely into flower buds using rostrum. Larval feeding destroys the reproductive capacity of infested flower heads. Adults capable of flight and dispersal to new thistle patches.

Biological control agent for invasive thistles, reducing plant competitive ability and seed production. However, documented feeding on native North American thistles creates ecological conflict, potentially threatening endemic species and pollinators dependent on native thistles.

Introduced deliberately for classical biological control of agricultural weeds, particularly Canada thistle. Reduces thistle infestations in pastures and agricultural lands, decreasing economic losses. Conservation concern due to non-target impacts on native thistles; USDA cancelled interstate movement permits in 2000.

• Rhinocyllus conicusSimilar size, ecology, and host use; distinguished by shorter rostrum and different egg-laying behavior (eggs deposited on bracts and leaves rather than drilled into buds)
• Larinus planusFormerly considered conspecific or closely related; now generally treated as distinct species with similar biology and host range

• biological control
• invasive species
• weed management
• conservation concern
• Curculionidae
• Coleoptera
• thistle herbivore
• classical biological control
• non-target effects
• seed predator

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Eaters of thistles: Thistle tortoise beetle, Cassida rubiginosa, and Canada thistle bud weevil, Larinus planus — Bug of the Week
• Archive — Bug of the Week
• Dr. Jekyll and Mr. Hyde wage war on thistles: Thistle head weevils, Rhinocyllus conicus — Bug of the Week