Rice Weevil

Sitophilus oryzae

Synonym - Calandra oryzae USA

Family: Curculionidae

Order: Coleoptera

Description:

Adult - Its weight is 0.6-1.5 mg with an average of 1.01 mg and the average length of females is 2.69 mm and males 2.46 mm.

Colour - Brown.

Body - Pronotum and elytra densely but irregularly punctulate.

Wings - Flight wings are well developed. Light brown elytra with spots that are not very apparent.

Mouthparts -

Antennae -

Legs -

Head - The rostrum is 1 mm long.

Thorax -

Abdomen - Abdominal tergites are light brown.

Egg - Whitish, oval and 0.7 mm long.

Habits -

Larva - Grub like, legless and cylindrical with a red brown head. Grows to 3-4 mm long.

Colour -

Body - Cylindrical

Mouthparts -

Antennae -

Legs - Legless

Head - Red brown

Thorax -

Abdomen -

Habits -

Pupa - Whitish and 3-3.5 mm long.

Biology:

At temperatures below 130C development ceases and it often does not survive the winter in cool climates.

Optimum temperature is 25-270C and populations may increase 7 times during one generation.

Eggs die at -20C for 20 days but adults can survive at this temperature for 40 days.

Adults can survive for extended periods without food providing humidity is high.

100 beetles produced 1400 mature offspring and destroyed 2500 Wheat grains or 80 g of Wheat in a 12 month period in one study.

It can fly about 2 km from it place of birth.

On warm days they will emerge from cracks in storage areas and fly to infest grain in the field. They rarely survive in the field for extended periods but this may be the source of new infestations in clean storage areas.

Eggs are rarely laid on flour or milled products.

Adults can attack a range of plant products but the larva can only develop in cereal grain.

The order of preference for infestation is Corn, Wheat, Barley, hard Wheat then other cereals.

They prefer dark areas and the major infestations in storage occur in the lower levels, close to the walls of the silo.

The grain moisture content must be greater than 9% for the weevils to develop.

Temperatures of 550C for 2 hours kills all stages of the weevil.

Life Cycle:

The female bores a small hole in the grain with its rostrum and deposit a single egg and then plugs the hole with a clear, gelatinous substance. The larva hatch within the grain and starts feeding. It then pupates within the grain and emerges as an adult. The young females will start to lay eggs about a week after emergence. The life cycle takes about a month in summer and 6 weeks in autumn and spring. In winter few eggs are laid and adults that emerge in autumn may live for up to 6 months. Normally adults survive for 3-4 months and produce 380 eggs on average with a maximum of around 600 recorded. Up to 4 eggs per day are laid. There are 5-6 generations per year.

Habitats:

Origin and History:

Probably originated in India.

Distribution:

Significance:

Found in storage areas in many countries, but is only a problem in the field in tropical areas.

The adults mainly attack grain but will infest milled products, meal, macaroni, crackers, fresh and dried fruit, tobacco and similar plant products.

The larva can only develop in cereal grain.

In dry, sealed storage conditions it is rarely a problem whereas in poor storage conditions losses of 40-50% are recorded.

Apple trees are occasionally attacked especially if close to cereal fields, storage areas or where infested chicken manure is used under tea trees.

Management and Control:

Heating products to 550C for 2 hours provides control of all stages.

Ensure storage areas are clean, dry, well sealed and well aerated.

Fumigation is sometimes used.

At least two parasites attack the weevil but have little effect on populations.

Some populations are resistant to chlorpyrifos-methyl.

Methoprene is ineffective.

Related Species:

Granary Weevil (Sitophilus granarius)

Similar Species:

Granary Weevil (Sitophilus granarius)

Lesser Grain Borer (Rhyzopertha dominica)

Rust-red Flour Beetle (Tribolium castaneum)

Sawtoothed Grain Beetle (Oryzaephilus surinamensis)

References:

CSIRO. The Insects of Australia. Melbourne University Press. (1991)

WADA. Insects and Allied Pests of Extensive Farming. Department of Agriculture - Western Australia Bulletin No. 4185.

Avidov, Z. and Harpaz, I. (1969) Plant Pest of Israel. Israel University Press. P297-300.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.