The rice weevil (''Sitophilus oryzae'') is a stored product pest which attacks seeds of several

crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. In other words, a crop is a plant or plant product that is grown for a specific purpose such as food, Fiber, fibre, or fuel. When plants of the same spe ...

s, including

wheat Wheat is a group of wild and crop domestication, domesticated Poaceae, grasses of the genus ''Triticum'' (). They are Agriculture, cultivated for their cereal grains, which are staple foods around the world. Well-known Taxonomy of wheat, whe ...

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

, and

maize Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...

Description

The adults are usually between long, with a long snout. The body color appears to be brown/black, but on close examination, four orange/red spots are arranged in a cross on the wing covers. It is easily confused with the similar looking

maize weevil The maize weevil (''Sitophilus zeamais''), known in the United States as the greater rice weevil, is a species of beetle in the family Curculionidae. It can be found in numerous tropical areas around the world, and in the United States, and is a m ...

. The maize weevil is typically somewhat larger than the rice weevil, but rice weevils as large as the largest maize weevils and maize weevils nearly as small as the smallest rice weevils have been found. Some external features can be used to differentiate the vast majority of adults, but the only reliable features are on the genitalia (see table below). Both species can hybridize. The genitalic structure of hybrids is unknown.

Biology

Adult rice weevils are able to fly, and can live for up to two years. Females lay 2–6 eggs per day and up to 300 over their lifetime. The female uses strong mandibles to chew a hole into a grain kernel after which she deposits a single egg within the hole, sealing it with secretions from her

ovipositor The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typica ...

. 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 ...

develops within the grain, hollowing it out while feeding. It then pupates within the grain kernel and emerges 2–4 days after

eclosion 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 ...

. Male ''S. oryzae'' produce an aggregation pheromone called sitophilure ((4S,5R)-5-Hydroxy-4-methylheptan-3-one) to which males and females are drawn. A synthetic version is available which attracts rice weevils, maize weevils and grain weevils. Females produce a pheromone which attracts only males. Its gammaproteobacterial symbiont ''Candidatus Sodalis pierantonius'' str. SOPE is able to supply rice weevil with essential vitamins like pantothenic acid, riboflavin, and biotin. During larvae development, bacteria rely on up-regulation of

type three secretion system The type III secretion system (T3SS or TTSS) is one of the bacterial secretion systems used by bacteria to secretion, secrete their Bacterial effector protein, effector proteins into the host's cells to promote virulence and Colonisation (biology ...

genes and genes for flagellum so they can infect insect stem cells.

Control

Control of weevils involves locating and removing all potentially infested food sources. Rice weevils in all stages of development can be killed by freezing infested food below −18 °C (0 °F) for a period of three days, or heating to 60 °C (140 °F) for a period of 15 minutes.

References

{{Authority control Beetles described in 1763 Dryophthorinae Storage pests Taxa named by Carl Linnaeus Insect pests of rice

Description

Biology

Control

See also

References