''Eustenopus villosus'' 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 yellow starthistle hairy 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 the
noxious weed
A noxious weed, harmful weed or injurious weed is a weed that has been designated by an agricultural or other governing authority as a plant that is harmful to agricultural or horticultural crops, natural habitats or ecosystems, or humans or lives ...
yellow starthistle (''Centaurea solstitialis'').
The adult weevil is hairy and brown with white stripes. It is 4 to 6 millimeters long, not including its long snout. The female chews a hole in a closed
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 ...
, deposits an egg inside, and seals the hole with a dark-colored
mucilage
Mucilage is a thick gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion, with the direction of their movement always opposite to that of the secretion of ...
. This visible hole can change the shape of the flower head as it grows. 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 from its egg in about three days and begins to feed on the flower parts and developing seeds. In just over two weeks the larva can destroy all or nearly all of the developing seeds. It uses the scraps to build a chamber in which it
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 for one to two weeks and then leaves the flower head as an adult. Both larvae and adults of this species contribute to the damage done to the plant. The larvae eat the seeds in mature flower buds and the adults feed on smaller buds, destroying many. This weevil will readily attack many invasive ''Centaurea'' species, but has not been known to damage native flora.
This weevil is native to southern Europe and the Mediterranean. It was first released as a biocontrol agent in the United States in 1990 and it is now established in much of the western United States wherever yellow starthistle grows. It is considered one of the more efficient yellow starthistle biocontrol agents.
References
* Coombs, E. M., et al., Eds. (2004). ''Biological Control of Invasive Plants in the United States''. Corvallis: Oregon State University Press, 427.
External links
USACE Biocontrol Profile
Lixinae
Insects used for control of invasive plants
Biological pest control beetles
{{Curculionidae-stub