''Larinus obtusus'' is a species of

true weevil The Curculionidae are a family of weevils, commonly called snout beetles or true weevils. They are one of the largest animal families with 6,800 genera and 83,000 species described worldwide. They are the sister group to the family Brentidae ...

known as the blunt knapweed flower weevil. It is used as an agent of

biological pest control Biological control or biocontrol is a method of controlling pests, whether pest animals such as insects and mites, weeds, or pathogens affecting animals or plants by using other organisms. It relies on predation, parasitism, herbivory, or ot ...

against noxious knapweeds, especially spotted knapweed (''Centaurea maculosa''). The adult weevil is dark brown with a large, bulbous snout. It is 5 to 7 millimeters (0.19 to 0.27 inches) long in total. It is active throughout the summer when the female lays yellow eggs in the opened

flower head A pseudanthium (; : pseudanthia) is an inflorescence that resembles a flower. The word is sometimes used for other structures that are neither a true flower nor a true inflorescence. Examples of pseudanthia include flower heads, composite flowers ...

. The

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

emerges and feeds on the developing seeds inside the head. The larval stage lasts 17 days, after which the larva constructs a cocoon from the remnants of the seeds and

pupa A pupa (; : pupae) is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages th ...

tes within it for about nine days. Most of the damage to the plant is done by the larva's feeding on the seeds; the adult feeds on the foliage but does less drastic damage to the plant. The average lifespan of the weevil is around 94 days for males and 58 for females. This weevil is native to Europe and the Middle East. It was first introduced to the United States for the biocontrol of knapweeds in the Boulder, Colorado area in 1991. It is now established in much of the northwestern United States, but its abundance is unknown. This weevil is quite similar to its relative, '' Larinus minutus'', which is also a knapweed specialist used for biocontrol. They are currently considered separate species but this could change with further research.

References

* Coombs, E. M., et al., Eds. (2004). ''Biological Control of Invasive Plants in the United States''. Corvallis: Oregon State University Press, 216.

External links

Cornell Biocontrol Profile
Lixinae Insects used for control of invasive plants Biological pest control beetles Beetles described in 1836 Taxa named by Leonard Gyllenhaal {{Curculionidae-stub