''Larinus minutus'' is a species of

true weevil True most commonly refers to truth, the state of being in congruence with fact or reality. True may also refer to: Places * True, West Virginia, an unincorporated community in the United States * True, Wisconsin, a town in the United States * T ...

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

biological pest control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...

against noxious

knapweeds ''Centaurea'' () is a genus of over 700 species of herbaceous thistle-like flowering plants in the family Asteraceae. Members of the genus are found only north of the equator, mostly in the Eastern Hemisphere; the Middle East and surrounding reg ...

, especially

diffuse knapweed ''Centaurea diffusa'', also known as diffuse knapweed, white knapweed or tumble knapweed, is a member of the genus ''Centaurea'' in the family Asteraceae. This species is common throughout western North America but is not actually native to the ...

(''Centaurea diffusa'') and

spotted knapweed ''Centaurea stoebe'', the spotted knapweed or panicled knapweed, is a species of ''Centaurea'' native to eastern Europe, although it has spread to North America, where it is considered an invasive species. It forms a tumbleweed, helping to in ...

. The adult weevil is dark mottled brown with a long snout. It is long in total. It is active throughout the summer with a 14-week maximum adult lifespan. During this time the female lays up to 130 eggs, depositing them in the knapweed

flower head A pseudanthium (Greek for "false flower"; ) 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, compos ...

. The

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

emerges and burrows into the flower head where it feeds on the developing seeds. The larva damages the plant by reducing seed production (all of the seeds of diffuse knapweed and 25-100% of spotted knapweed) and the adult does damage by defoliating the plant as it feeds on the leaves prior to flowering. After flowering, adult weevils switch to feeding on flowers. In spotted and diffuse knapweed, ''L. minutus'' directly consumes another biological control agent released to control the species, the gall-forming flies ''

Urophora affinis ''Urophora affinis'' is a species of tephritid or fruit flies in the genus ''Urophora'' of the family Tephritidae. It has been released in the United States and Canada as a biocontrol agent to control spotted knapweed. ''U. affinis'' became estab ...

'' Frfld and '' Urophora quadrifasciata'' Meigen (Diptera: Tephrididae) This weevil is native to southern Europe and the Mediterranean. It was first released as a knapweed biocontrol in the United States in 1991 from Greece.Lang, R.F., Story, J.M., Piper, G.L., 1996. Establishment of ''Larinus minutus'' Gyllenhal (Coleoptera: Curculionidae) for biological control of diffuse and spotted knapweed in the western United States. Pan Pacific Entomology 72, 209–212. It is now established in knapweed populations throughout the western United States, especially in warm, dry areas. It feeds on knapweeds, preferring diffuse knapweed over others, and it has not been shown to attack native flora. This weevil has been shown to reduce diffuse knapweed density at several sites. It has been less successful in controlling spotted knapweed.Smith, L., 2004. Impact of biological control agents on Centaurea diffusa (diffuse knapweed) in central Montana. In: Cullen, J.M., Briese, D.T., Kriticos, D.J., Lonsdale, W.M., Morin, L., Scott, J.K. (Eds.), Proceedings of the XI International Symposium on Biological Control of Weeds. CSIRO, Canberra, pp. 589–593.Story, J.M., Callan, N.W., Corn, J.G., White, L.J., 2006. Decline of spotted knapweed density at two sites in western Montana with large populations of the introduced root weevil, ''Cyphocleonus achates'' (Fahraeus). Biological Control 38, 227–232.

References

*Coombs, E. M., et al., Eds. (2004). ''Biological Control of Invasive Plants in the United States''. Corvallis: Oregon State University Press, 214. *Smith, L., Mayer, M., 2005. Field cage assessment of interference among insects attacking seedheads of spotted and diffuse knapweed. Biocontrol Science and Technology 15, 427–442.

External links

Cornell Biocontrol Profile
{{DEFAULTSORT:Larinus Minutus Lixinae Insects used for control of invasive plants Biological pest control beetles