Non-target-effects
Guides
Bruchidius villosus
broom seed beetle, Scotch broom bruchid
Bruchidius villosus is a small seed-feeding beetle in the family Chrysomelidae, native to Europe and introduced to North America and New Zealand as a biological control agent for Scotch broom (Cytisus scoparius). It has been deliberately released in the United States since the 1990s to reduce seed production in this invasive weed. In New Zealand, it has exhibited problematic host range expansion to non-target leguminous plants. The species is approximately 2 mm in length with dark gray coloration.
Chrysolina quadrigemina
greater St. John's wort beetle, St. John's wort beetle
Chrysolina quadrigemina is a leaf beetle introduced to North America as a biological control agent for the invasive weed Hypericum perforatum (St. John's wort). Native to Europe and North Africa, this beetle has established populations across western North America and has been introduced to Australia. Adults and larvae feed exclusively on Hypericum species, with documented spillover onto native congeners such as H. punctatum in the eastern United States. The beetle exhibits a univoltine life cycle with adults active in summer, and shows evidence of post-colonization adaptation to colder climates in northern populations.
Compsilura concinnata
European Tachinid Fly
Compsilura concinnata is a polyphagous tachinid fly native to Europe that was introduced to North America in 1906 as a biological control agent for the spongy moth (Lymantria dispar). It is an endoparasitoid of insect larvae, developing within the host midgut and eventually killing it. The species attacks over 200 host species across Coleoptera, Lepidoptera, and Hymenoptera, but has proven ineffective against its intended target while causing significant non-target impacts on native Lepidoptera, including giant silk moths and monarch butterflies.
Larinus carlinae
Canada thistle bud weevil, thistle bud weevil, Canada thistle stem weevil
A small weevil native to Europe and western Asia introduced to North America as a biological control agent for invasive thistles. Adults emerge in spring and feed on developing thistle buds with their elongated snouts. Females drill into flower buds to deposit eggs; larvae hatch and consume reproductive tissues, destroying seeds and preventing plant reproduction. Populations can reduce target thistle species by 90% or more within a decade of establishment. The species has been observed feeding on native North American thistles, raising conservation concerns for endemic species.
Rhinocyllus
thistle head weevil
Rhinocyllus is a small genus of true weevils (Curculionidae) comprising four described species. The genus is notable for its specialized association with thistles in the subtribe Carduinae. The most widely known species, R. conicus, was introduced to North America in the 1960s as a biological control agent for invasive thistles including musk thistle (Carduus nutans), but subsequently revealed significant non-target impacts on native North American thistles, including threatened and endangered species. The genus is sister to Bangasternus.
Rhinocyllus conicus
thistle head weevil, nodding thistle receptacle weevil
Rhinocyllus conicus is a small true weevil native to Eurasia and North Africa, introduced to North America in 1969 as a biological control agent for invasive thistles. Adults are black with yellowish mottled hairs, up to 6 mm long, with a short snout. Females lay eggs on thistle flower heads, which larvae enter to feed on developing seeds and flower parts, preventing seed production. While effective at controlling invasive thistles like musk thistle, the weevil was found to attack native North American thistles as well, leading to cancellation of its distribution permits in 2000.