Weevil

This article is about the beetles. For other uses, see Weevil (disambiguation).
Weevils
Lixus angustatus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Suborder: Polyphaga
Infraorder: Cucujiformia
Superfamily: Curculionoidea
Latreille, 1802
Families

A weevil is a type of beetle from the Curculionoidea superfamily. They are usually small, less than 6 mm (0.24 in), and herbivorous. Over 60,000 species are in several families, mostly in the family Curculionidae (the true weevils). Some other beetles, although not closely related, bear the name "weevil", such as the biscuit weevil (Stegobium paniceum), which belongs to the family Anobiidae.

Many weevils are considered pests because of their ability to damage and kill crops. The grain or wheat weevil (Sitophilus granarius) damages stored grain. The boll weevil (Anthonomus grandis) attacks cotton crops. It lays its eggs inside cotton bolls, and the larvae eat their way out.

One species of weevil, Austroplatypus incompertus, exhibits eusociality, one of the few organisms outside the Hymenoptera to do so.

Taxonomy

Because so many species exist in such diversity, the higher classification of weevils is in a state of flux. They are generally divided into two major divisions, the Orthoceri or primitive weevils, and the Gonatoceri or true weevils (Curculionidae). E. C. Zimmerman proposed a third division, the Heteromorphi, for several intermediate forms.[1] Primitive weevils are distinguished by having straight antennae, while true weevils have elbowed (geniculate) antennae. The elbow occurs at the end of the scape (first antennal segment) in true weevils, and the scape is usually much longer than the other antennal segments. Some exceptions occur. Nanophyini are primitive weevils (with very long trochanters), but have long scapes and geniculate antennae. From the true weevils, Gonipterinae and Ramphus have short scapes and little or no elbow.

The most recent classification system to family level was provided by Kuschel,[2] with updates from Marvaldi et al.,[3] and was achieved using phylogenetic analyses. The accepted families are the primitive weevils, Anthribidae, Attelabidae, Belidae, Brentidae, Caridae, and Nemonychidae, and the true weevils Curculionidae. Most other weevil families were demoted to subfamilies or tribes. Weevil species radiation was shown to follow steps in plant evolution upon which the weevils feed; they can vary in color from black to light brown.

Some of the features used to distinguish weevil families are:

Labrum visible as separate segment to clypeus Anthribidae, Nemonychidae
Antennae elbowed most Curculionidae, Nanophyini (Apioninae)
Trochanters (segment between coxae and femora) as long or longer than coxae Apioninae including Nanophyini
Fore tibia with comb of setae in apical groove opposite tarsal articulation Belidae
Elytra striate (with longitudinal ridges or grooves) Brentidae, Curculionidae, Rhinorhynchinae
Rostrum short and broad Anthribidae, some Curculionidae (some Brachycerinae including Ithycerus (New York weevil), Scolytinae and Platypodinae).
Maxillary palps long and projecting (visible from above at tip of rostrum) Anthribidae, Nemonychidae
Abdominal tergites 6 and 7 without spiracles Caridae
Gular suture (on ventral part of head) single not double Attelabidae, Brentidae, Curculionidae.

Sexual dimorphism

Rhopalapion longirostre exhibits an extreme case of sexual dimorphism. The female rostrum is twice as long and its surface is smoother than in the male. The female bores egg channels into the buds of Alcea rosea. Thus, the dimorphism is not attributed to sexual selection. It is a response to ecological demands of egg deposition.[4]

Phylogeny

A phylogeny of the Curculionoidea based on 18S ribosomal DNA and morphological data is suggested below:[3]


Nemonychidae

Anthribidae

Belidae

Attelabidae

Caridae

Brentidae

Curculionidae







Gallery

References

  1. ↑ E. C. Zimmerman (1994). Australian weevils (Coleoptera: Curculionidae). Volume 1. Orthoceri: Anthribidae to Attelabidae: the primitive weevils. East Melbourne: CSIRO. pp. 741 pp.
  2. ↑ G. Kuschel (1995). "A phylogenetic classification of Curculionoidea to families and subfamilies". Memoirs of the Entomological Society of Washington 14: 5–33.
  3. 1 2 A. E. Marvaldi, A. S. Sequeira, C. W. O'Brien & B. D. Farrell (2002). "Molecular and morphological phylogenetics of weevils (Coleoptera, Curculionidae): do niche shifts accompany diversification?". Systematic Biology 51 (5): 761–785. doi:10.1080/10635150290102465. PMID 12396590.
  4. ↑ G. Wilhelm; et al. (2011). "Sexual dimorphism in head structures of the weevil Rhopalapion longirostre: a response to ecological demands of egg deposition". Biological Journal of the Linnean Society 104: 642–660. doi:10.1111/j.1095-8312.2011.01751.x.

Further reading

External links

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