Weevil
| Weevil | |
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| Acorn weevil, Curculio sp. | |
| Scientific classification | |
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| Superfamily: | Curculionoidea Latreille, 1802
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| Families | |
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Anthribidae — fungus weevils | |
A weevil is any beetle from the Curculionoidea superfamily. They are usually small, less than 6 mm (¼ inch), and herbivorous. Due to the shape of their heads, weevils are commonly known as snout beetles. There are over 60,000 species 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 damaging to crops. The grain or wheat weevil (Sitophilus granarius) damages stored grain. The boll weevil (Anthonomus grandis) attacks cotton crops. It lays its eggs inside unripe cotton bolls, and the young weevils eat their way out.
Weevils are often found in dry foods including nuts and seeds, cereal and grain products. In the domestic setting, they are most likely to be observed when opening a bag of flour although they will happily infest most types of grain including oats, barley and breakfast cereals. If ingested, E. coli infection and other various diseases can be contracted from weevils, depending on their diet.
Taxonomy
Because there are so many species and such diversity, the higher classification of weevils is in a state of flux. Weevils are generally divided into two major divisions, the Orthoceri or primitive weevils, and the Gonatoceri or true weevils (Curculionidae). 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.
Some of the features used to distinguish weevil families are:
| Labrum visible as separate segment to clypeus | Anthribidae, Nemonychidae |
| Antennae elbowed | most Curculionidae, Nanophyini of 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. |
Phylogeny
A phylogeny of the Curculionoidea based on 18S ribosomal DNA and morphological data is suggested below:[3]
References
- ^ E. C. Zimmerman (1994). Australian weevils (Coleoptera: Curculionoidea). Volume 1. Orthoceri: Anthribidae to Attelabidae: the primitive weevils. CSIRO, East Melbourne. pp. 741 pp.
- ^ G. Kuschel (1995). "A phylogenetic classification of Curculionoidea to families and subfamilies". Memoirs of the Entomological Society of Washington. 14: 5–33.
{{cite journal}}: Unknown parameter|quotes=ignored (help) - ^ a b A. E. Marvaldi, A. S. Sequeira, C. W. O'Brien & B. D. Farrell (2002). "Molecular and morphological phylogenetics of weevils (Coleoptera, Curculionoidea): do niche shifts accompany diversification?". Systematic Biology. 51 (5): 761–785.
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