T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Weevil (Rice) Sitophilus oryzae

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Curculionidae
Subfamily: Dryophthorinae
Tribe: Litosomini
Genus: Sitophilus
Species: S. oryzae
Binomial name: Sitophilus oryzae
Common name: Rice weevil, Lesser grain weevil

Sitophilus oryzae is a stored product pest which infests wheat, oats, rye, barley, rice, beans, sunflower seeds and corn. These insects are cosmopolitan in distribution and have originated in the Far East region. They are usually found in grain storage and processing plants. 

The adults are around 2 mm long and they have a long characteristic rostrum (snout or beak) and elbowed antennae of the family Curculionidae. The body colour appears to be brown/black, but on close examination, there are four orange/red spots on corners of the elytra (wing covers). The prothorax is strongly pitted, and the elytra have rows of pits within longitudinal grooves.
Adult Sitophilus oryzae are able to fly and can survive for up to two years. The 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 eggs are shiny, white, opaque and ovoid to pear-shaped. The larva develops within the grain, hollowing it out while feeding. These developmental stages are all found within tunnels and chambers bored in the grain and are thus not normally seen. The larva is white, stout and legless and feeds inside the kernel for 18 days. It periodically moults to increase size. The pupa is also white, but it has legs, wings, and the snout of the fully-grown weevil. The pupal stage lasts for 6 days. It then pupates within the grain kernel and emerges 2–4 days after eclosion (emerging from the pupal case). The full life cycle may take only 26 to 32 days during hot summer months but requires a much longer period during cooler weather.

Male S. orzyae produce an aggregation pheromone ((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.

A 2 mm long adult.

The larvae.
  

Thanks to Wikipedia for text and information:
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