Larinus minutus

Larinus minutus is a species of true weevil known as the lesser knapweed flower weevil. It is used as an agent of biological pest control against noxious knapweeds, especially diffuse knapweed (Centaurea diffusa) and spotted knapweed.

Larinus minutus
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Insecta
Order:
Coleoptera
Family:
Curculionidae
Genus:
Larinus
Species:
L. minutus
Binomial name
Larinus minutus

The adult weevil is dark mottled brown with a long snout. It is 4 or 5 millimetres (0.16 or 0.20 in) 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. The larva 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)[1] and the adult does damage by defoliating the plant as it feeds on the leaves prior to flowering.[2][3][4] After flowering, adult weevils switch to feeding on flowers.[5]

In spotted and diffuse knapweed, L. minutus directly consumes another biological control agent released to control the species, the gall-forming flies Urophora affinis Frfld and Urophora quadrifasciata Meigen (Diptera: Tephrididae) [6]

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.[1] 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.[7][8] It has been less successful in controlling spotted knapweed.[6][8][9]

References
  1. 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.
  2. Wilson, L.M., Randall, C.B., 2003. Biology and Biological Control of Knapweed. Forest Health Technology Enterprise Team, Technology Transfer.
  3. Piper, G.L., 2004. Biotic suppression of invasive weeds in Washington state: a half-century of progress. 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. 584–588.
  4. Norton, A.P., Blair, A.C., Hardin, J.G., Nissen, S.J., Brunk, G.R., 2008. Herbivory and novel weapons: no evidence for enhanced competitive ability or allelopathy induction of Centaurea diffusa by biological controls. Biological Invasions 10, 79–88.
  5. Blair (2008). "How do biological control and hybridization affect enemy escape?" (PDF). Biological Control 46 (2008) 358–370. Archived from the original (PDF) on 2010-08-08.
  6. Seastedt, T.R.; Knochel, D.G.; Garmoe, M.; Shosky, S.A. (2007). "Interactions and effects of multiple biological control insects on diffuse and spotted knapweed in the Front Range of Colorado" (PDF). Biological Control. pp. 345–354. Archived from the original (PDF) on 14 August 2011.
  7. Seastedt, T.R., Gregory, N., Buckner, D., 2003. Effect of biocontrol insects on diffuse knapweed (Centaurea diffusa) in a Colorado grassland. Weed Science 51, 237–245.
  8. 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.
  9. 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.
  • 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.
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