Larinus minutus
Encyclopedia
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.
The adult weevil is dark mottled brown with a long snout. It is 4 or 5 millimeters 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) 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
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. 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 diffuse knapweed density at several sites. It has been less successful in controlling spotted knapweed.
Curculionidae
Curculionidae is the family of the "true" weevils . It was formerly recognized in 1998 as the largest of any animal family, with over 40,000 species described worldwide at that time...
known as the lesser knapweed flower weevil. It is used as an agent of biological pest control
Biological pest control
Biological control of pests in agriculture is a method of controlling pests that relies on predation, parasitism, herbivory, or other natural mechanisms...
against noxious knapweeds
Centaurea
Centaurea is a genus of between 350 and 600 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 regions are particularly species-rich...
, especially diffuse knapweed
Diffuse knapweed
Diffuse Knapweed , also known as White Knapweed or Tumble Knapweed, is a member of the genus Centaurea in the family Asteraceae. It is native to Asia Minor , the Balkans, , Ukraine, and southern Russia. Diffuse knapweed is an annual or biennial plant, generally growing to between 10 and 60 cm...
(Centaurea diffusa) and spotted knapweed.
The adult weevil is dark mottled brown with a long snout. It is 4 or 5 millimeters 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
Head (botany)
The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....
. The larva
Larva
A larva 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...
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
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 established in Montana in 1973.-Life History:U. affinis is...
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. 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 diffuse knapweed density at several sites. It has been less successful in controlling spotted knapweed.