Weevil

Weevils
Lixus angustatus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Suborder: Polyphaga
Infraorder: Cucujiformia
Superfamily: Curculionoidea
Latreille, 1802
Families

Weevils are certain beetles, namely the ones belonging to the Curculionoidea superfamily. They are usually small, less than 6 mm (0.24 in), and herbivorous. About 97,000 species of weevils are known. They belong to several families, with most of them 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 Ptinidae.

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 balls and the larvae eat their way out. Other weevils are used for biological control of invasive plants.

Some weevils have the ability to fly, such as the rice weevil.[1][2]

One species of weevil, Austroplatypus incompertus, exhibits eusociality, one of the few insects outside the Hymenoptera and the Isoptera 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.[3] 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,[4] with updates from Marvaldi et al.,[5] 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 clypeusAnthribidae, Nemonychidae
Antennae elbowedmost Curculionidae, Nanophyini (Apioninae)
Trochanters (segment between coxae and femora) as long or longer than coxaeApioninae including Nanophyini
Fore tibia with comb of setae in apical groove opposite tarsal articulationBelidae
Elytra striate (with longitudinal ridges or grooves)Brentidae, Curculionidae, Rhinorhynchinae
Rostrum short and broadAnthribidae, 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 spiraclesCaridae
Gular suture (on ventral part of head) single not doubleAttelabidae, 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.[6]

Phylogeny

A phylogeny of the Curculionoidea based on 18S ribosomal DNA and morphological data is suggested below:[5]

 

 

 

Nemonychidae

 
 

Anthribidae

 
 
 

 

Belidae

 
 

 

Attelabidae

 
 

 

Caridae

 
 

 

Brentidae

 
 

Curculionidae

 
 
 
 
 
 

References

  1. ↑ "What Is a Weevil and How Did That Bug Get in My Food?".
  2. ↑ "Weevils on Stored Grain (Department of Entomology)". Department of Entomology (Penn State University).
  3. ↑ E. C. Zimmerman (1994). Australian weevils (Coleoptera: Curculionidae). Volume 1. Orthoceri: Anthribidae to Attelabidae: the primitive weevils. East Melbourne: CSIRO. pp. 741 pp.
  4. ↑ G. Kuschel (1995). "A phylogenetic classification of Curculionoidea to families and subfamilies". Memoirs of the Entomological Society of Washington. 14: 5–33.
  5. 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.
  6. ↑ 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

  • Bright, Donald E.; Bouchard, Patrice (2008). Coleoptera, Curculionidae, Entiminae: Weevils of Canada and Alaska Volume 2. Insects and Arachnids of Canada Series, Part 25. Ottawa: NRC Research Press. ISBN 978-0-660-19400-4.
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