Wheat weevil

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Wheat weevil
COLE Curculionidae Sitophilus granarius.png
Illustration by Des Helmore
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Infraorder: Cucujiformia
Family: Curculionidae
Subfamily: Dryophthorinae
Tribe: Litosomini
Genus: Sitophilus
Species:
S. granarius
Binomial name
Sitophilus granarius
Synonyms
  • Calandra frumentarius Stephens, 1829
  • Calandra granaria(Clairville and Schellenberg, 1798)
  • Calandra laevicostaPhilippi and Philippi, 1864
  • Calandra remotepunctata(Gyllenhaal, 1838)
  • Calandra remotepunctatus(Gyllenhaal, 1838)
  • Cordyle granarius(Thunberg, 1815)
  • Curculio granarius Linnaeus, 1758
  • Curculio pulicarius Panzer, 1798
  • Curculio segetis Linnaeus, 1758
  • Curculio unicolor Marsham, 1802
  • Rhynchaenus segetis(Latreille, 1804)
  • Rhynchophorus granarius(Herbst, 1795)
  • Sitophilus remotepunctatus(Gyllenhaal, 1838)

The wheat weevil (Sitophilus granarius), also known as the grain weevil or granary weevil, is an insect that feeds on cereal grains, and is a common pest in many places. It can cause significant damage to harvested stored grains and may drastically decrease crop yields. The females lay many eggs and the larvae eat the inside of the grain kernels.

Contents

Identification

Adult wheat weevils are about 3–5 mm (0.12–0.20 in) long with elongated snouts and chewing mouth parts. [2] Depending on the grain kernels, the size of the weevil varies. In small grains, such as millet or grain sorghum, they are small in size, but are larger in maize (corn). [3] The adults are a reddish-brown colour and lack distinguishing marks. Adult wheat weevils are not capable of flight. Larvae are legless, humpbacked, and are white with a tan head. Weevils in the pupal stage have snouts like the adults.

Natural history

Life cycle

Female wheat weevils lay between 36 and 254 eggs and usually one egg is deposited in each grain kernel. All larval stages and the pupal stage occur within the grain. The larvae feed inside the grain until pupation, after which they bore a hole out of the grain and emerge. They are rarely seen outside of the grain kernel. The life cycle takes about five weeks in the summer, but may take up to 20 weeks in cooler temperatures. [4] Adults can live up to eight months after emerging.

Behavior

Adult wheat weevils when threatened or disturbed will pull their legs close to their bodies and feign death. Female weevils can tell if a grain kernel has had an egg laid in it by another weevil. [5] They avoid laying another egg in this grain. Females chew a hole, deposit an egg, and seal the hole with a gelatinous secretion. This may be how other females know the grain has an egg in it already. This ensures the young will survive and produce another generation. One pair of weevils may produce up to 6,000 offspring per year.

The species is not found "in the wild", but only in human food-storage situations. [6]

Human impact

Wheat weevils are pests of stores of grains of the cereal crops wheat, oats, rye, barley, rice and maize. Unfortunately the impact of wheat weevils worldwide is unknown because information is not well shared. It is believed to be especially bad in places where the grain harvests are not accurately measured. The weevils are hard to detect and usually all of the grain in an infested storage facility must be destroyed. Many methods have been attempted to get rid of the wheat weevil, such as pesticides, different methods of masking the odor of the grain with unpleasant scents, and some have even gone as far as introducing predator organisms. [7]

Prevention and control

Sanitation and inspection are key to preventing infestation. Grains should be stored in preferably metallic (cardboard, even fortified, is easily drilled through by the weevil) containers with tight lids in a refrigerator or a freezer, and should be purchased in small quantities. If any suspicion has arisen, carefully examine the grains for adult insects or holes in the grain kernels. Another method is to immerse them in water. If they float to the surface, it is a good indication of infestation. Even if identified early, disposal may be the only effective solution.[ citation needed ]

See also

Related Research Articles

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<span class="mw-page-title-main">Weevil</span> Superfamily of beetles

Weevils are beetles belonging to the superfamily Curculionoidea, known for their elongated snouts. They are usually small – less than 6 mm in length – and herbivorous. Approximately 97,000 species of weevils are known. They belong to several families, with most of them in the family Curculionidae. It also includes bark beetles, which while morphologically dissimilar to other weevils in lacking the distinctive snout, is a subfamily of Curculionidae. Some other beetles, although not closely related, bear the name "weevil", such as the biscuit weevil, which belongs to the family Ptinidae.

<span class="mw-page-title-main">Bookworm (insect)</span> Any insect that is said to bore through books

Bookworm is a general name for any insect that is said to bore through books.

<span class="mw-page-title-main">Drugstore beetle</span> Species of beetle

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<i>Sitophilus</i> Genus of beetles

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<span class="mw-page-title-main">African armyworm</span> Species of moth

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<span class="mw-page-title-main">Angoumois grain moth</span> Species of moth

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Pissodes nemorensis, known generally as the eastern pine weevil or deodar weevil, is a species of true weevil in the beetle family Curculionidae. It is found in North America and Africa. Deodar weevils are considered a forest pest in the United States, with adults and larvae feeding on a variety of coniferous tree species, including trees such as deodar cedar, loblolly pine, longleaf pine, sand pine, shortleaf pine, slash pine, and spruce pine Trees of all ages are susceptible to weevil infestations, while trees that are severely stressed by fire, drought, extreme cold, fusiform rust, wind damage, and other problems are prone to weevil infestation. In well-managed pine stands, deodar weevil infestations are sporadic, attacking only the suppressed and unhealthy trees throughout the area. Because they do not typically effect healthy trees, they do not usually alter traditional management strategies. Unlike many other forest pests in the eastern United States, deodar weevils are most active in the winter months, and this is often when sign of infestations can be seen. The best way to avoid a deodar weevil infestation is to maintain good tree and stand health: healthy trees do not typically face mortality or extensive damage from these pests. If an infestation has occurred, pesticides can be used in the fall as the weevils become active, but are typically not recommended.

A storage pest is an insect or other animal that damages or destroys stored food or other stored valuable organic matter. Insects are a large proportion of storage pests with each type of crop having specific insects that gravitate towards them such as the genus Tribolium that consists of insects such as Tribolium castaneum or Tribolium confusum which damage flour crops primarily.

References

  1. "Sitophilus granarius (Linnaeus, 1758)". Integrated Taxonomic Information System . Retrieved September 6, 2012.
  2. Akol, Anne M.; Chidege, Maneno Y.; Talwana, Herbert A.L.; Mauremootoo, John R. "Factsheet - Sitophilus granarius (Linnaeus, 1875) - Granary Weevil". BioNET-EAFRINET. Retrieved 2017-03-08.
  3. "Granary and Rice Weevils" (PDF). Retrieved 2009-01-21.
  4. "Store Products Pests: Granary Weevil" (PDF). Archived from the original (PDF) on 2009-09-01. Retrieved 2009-01-21.
  5. Woodbury, N. 2008. Infanticide Avoidance by the Granary Weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae): The Role of Harbourage Markers, Oviposition Markers, and Egg-Plugs. Journal of Insect Behavior, 21: 55-62.
  6. Patterson, Lindsay (8 January 2019). "Meet The Granary Weevil, The Pantry Monster Of Our Own Creation". NPR. Retrieved 9 January 2019.
  7. Giacinto, G. S., Antonio, D. C., & Giuseppe, R. 2008. Behavioral responses of adult Sitophilus granarius to individual cereal volatiles. Journal of Chemical Ecology, 34: 523-529.