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Rice Weevil

Rice Weevil (Sitophilus oryzae)

Rice Weevil (Sitophilus oryzae)

Structure, Appearance and Characteristics

 Adults:

  • Dark brown in colour.
  • 2.0 - 3.5mm long.
  • Long elongate snout characteristic of weevils.
  • Generally have four lighter coloured areas on the back, two on each wing cover which are light red to yellow in colour.
  • Pronotum is pitted with deep, round punctures.
  • Adults do not fly readily.
  • Bumping outside of bagged grain or walking on surface of bulk grain will cause adults to appear at the surface a few minutes later.  This is one method that can be used to detect an infestation.
  • Will feign death for a short period of time after being disturbed.
  • Chewing mouthparts.

Laveae (the young):

  • White in colour, head is tan to brownish black in colour.
  • Legless.
  • Chewing mouthparts.

Life Cycle

  • Complete metamorphosis.
  • Females produce 200 - 400 eggs in a lifetime.
  • Females lay eggs into holes bored into the whole grain and seal the holes with gelatinous fluid.
  • Larvae hatch inside the grain.
  • Larvae feed on inside of grain until pupation which happens inside the grain as well.
  • Larvae moult 3 times.
  • Average larval period is approx. 18 days.
  • Average pupation period is ranges from 3 - 9 days under ideal conditions.
  • After pupation, the adult remains inside the kernel for 3 - 4 days where it matures and hardens, after which it emerges from the kernel by chewing its way out.
  • Life cycle is completed in 28 days at 30 C, but longer than 15 weeks at 18 C, below which temperature reproduction appears to cease.
  • Adults generally live 2 - 3 months, but can live much longer (up to 6 months).

Habitat

Places where grain is stored. Primarily a pest in warmer climates.

Food

Feeds on small grains such as wheat, oats, barley, rice and sorghum.  It has also been reported infesting food products such as stored cotton, grapes, cashew nuts, cereals, wheat products and some fruits.  However food for the larva is restricted to seeds and grains since it spends its entire pre-adult life inside the kernel or seed.

Pest Status

Most important pest species infesting stored grain in Queensland.  It is the common weevil which attacks small grains such as wheat, oats, barley, rice and sorghum.  It usually does not attack maize.

Both adults and larvae are considered pests since both live on the same food source.

Control

Strengths include a high reproductive rate, quick maturity to adult stage, high reproduction in the early stages of adulthood and easy dispersal and migration which means a new colony can start quickly with only a few individuals to begin. Weaknesses include the need for optimum temperature, moisture content and relative humidity before prolific breeding will occur.

 Control measures include hygiene (incoming stock inspection, stock rotation, stock segregation, spillage control, warehouse design), aeration, drying, exclusion (screens etc.), chemical treatments (eg. Admixtures and surface sprays).  The objective of control measures is to STOP and infestation from occurring in the first instance.

 To remove a population from store products may require extreme measures such as fumigation or removal of the infected product from the premises followed by implementing adequate hygiene measures and chemical treatments to eliminate existing populations which may still exist in the storage area.

Our licensed technicians can assist you with a flexible, tailored solution to meet your needs and prevent these pests from becoming a problem in your home or workplace. Please contact us to see how we can help you maintain an environment free of these and other pests.

 


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