Rice weevil (Sitophilus oryzae) is a major pest in stored grain products like rice, maize, sorghum, corn, barley, wheat etc.

1. AB – 2111
POST HARVEST BIOLOGY
RICE WEEVIL
(Sitophilus oryzae )
By
N.H.G.T.Madushani (AG/12/FT/012)
W.A.G.E.Wijelath (AG/12/FT/024)
Department of Food Science and Technology
Faculty of Agriculture
University of Peradeniya

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Acknowledgement
We would like to thank Dr.K.S.Hemachandra for sharing his knowledge with us and for
guiling us in preparing this report on the morphology and life cycle of rice weevil.

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Content
1. Introduction…………………………4
2. Taxonomy………………………….. 4
3. Life Cycle………………………….. 4
4. Morphology………………………... 5
5. Behaviour………………………….. 7
6. Habitat………………………………7
7. Signs of Infestation………………… 8
8. Damages…………………………… 8
9. Control…………………………….. 8
10. References……………………….... 9

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1. Introduction
Rice weevil (Sitophilus oryzae) is a major pest in stored grain products like rice, maize,
sorghum, corn, barley, wheat etc. They grow in humid conditions with moderately high
temperature and result in the loss of nutritional and qualitative properties of the product.
The larval and adult stages of rice weevils damage the stored grain products and
knowledge on the morphology, life cycle, infested products and possible control
measures is vital in overcoming the damage caused by rice weevil.
2. Taxonomy
Kingdom : Animalia
Phylum : Arthropoda
Class : Insecta
Order : Coleoptera
Family : Curculionidae
Subfamily : Dryophthorinae
Genus : Sitophilus
Species : S.oryzae
3. Life Cycle
The life cycle of Sitophilus oryzae consists of four stages as egg stage, larval stage, pupa
stage and the adult stage. The adult female rice weevil lays an average of 4 eggs per day
and may live for four to five months (producing 250-400 eggs). The life cycle is
completed in around 28 days under favourable environmental conditions. The eggs hatch
in about 3 days. The larvae feed inside the grain kernel for an average of 18 days. The
pupal stage lasts an average of 6 days (5-16 range) and the adult stage emerges. The new
adult will remain in the seed for 3 to 4 days while its cuticle hardens and matures.

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Figure 1: Life cycle of Sitophilus oryzae
4. Morphology
The rice weevil (Figure 2) is small, 1/10 inch (2 to 3 mm) and has
a prominent stout. It is very similar in appearance to the granary
weevil. However, the rice weevil is reddish-brown to black in
colour with four light yellow or reddish spots on the corners of the
elytra (the hard protective forewings). The snout is long (1 mm),
almost 1/3 of the total length. The head with snout is as long as the
prothorax or the elytra. The prothorax is strongly pitted and the
elytra have rows of pits within longitudinal grooves. The larva is
legless and stays inside the hollowed grain kernel. It is fat with a
cream coloured body and dark head capsule.
The body colour appears to be brown or black, but on close
examination, four orange or red spots are arranged in a cross on
Figure 2: Adult rice weevil

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the wing covers. Rice weevil is easily confused with the similar looking maize weevil,
but there are several distinguishing features:
Rice weevil (S. oryzae) Maize weevil (S. zeamais) family :
Longitudinally elliptical punctures are
present on pronotal dorsum
Circular punctures are present on pronotal
dorsum
Pronotal punctures are separated by a
flat, median, longitudinal puncture-free
zone
Pronotal punctures have no median puncture-
free area and are nearly equally spaced apart
Less than 20 pronotal punctures are
present along the approximate midline,
running from neck to scutellum
More than 20 pronotal punctures are present
along the approximate midline, running from
neck to scutellum
Scutellar elevations are relatively closer
together compared to their longitudinal
Scutellar elevations relatively farther apart

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length compared to their longitudinal length
Scutellar elevations extend
longitudinally approximately more than
halfway down the scutellum
Scutellar elevations extend longitudinally
approximately halfway down the scutellum
Proepimera meets behind the fore coxae
and along the posterior edge, has a
distinct curved notch
Proepimera meets behind the fore coxae and has
a barely discernible notch along the posterior
edge at the site of the meeting
point
Aedeagus is smooth and shiny on the
dorsal surface
Aedeagus has two dorsal, longitudinal grooves
5. Behaviour
The adult rice weevil can fly and is attracted to lights. When disturbed, adults pull in their
legs, fall to the ground, and feign death. The larval rice weevil must complete its
development inside a seed kernel or a man-made equivalent, like macaroni products.
Larval rice weevils have been known to develop in hard caked flour. The adult female
eats a cavity into a seed and then deposits a single egg in the cavity, sealing in the egg
with secretions from her ovipositor. The larva develops within the seed, hollowing it out
while feeding. The larva then pupates within the hollow husk of the grain kernel.
6. Habitat
The rice weevil is one of the most serious stored grain pests worldwide. This pest of
whole grain originated in India and has been spread worldwide by commerce. It now has
a cosmopolitan distribution. It is a serious pest in the southern United States. The rice
weevil is replaced by the granary weevil north of North Carolina and Tennessee. Both the
adults and larvae feed on whole grains. They attack wheat, corn, oats, rye, barley,

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sorghum, buckwheat, dried beans, cashew nuts, wild bird seed, and cereal products,
especially macaroni.
7. Signs of Infestation
Heating of the grain surface and increase in the moisture level of stored grain products
can suggest the presence of rice weevil in the particular product. However, these
conditions may arise due to infestation by other insects too. The infestation of rice weevil
can be confirmed by the presence of live or dead rice weevils in the product and presence
of circular holes in the grain which is caused when the adult stage leaves the grain seed.
8. Damages
These weevils are very destructive grain pests. Of the three Sitophylus pests, the rice
weevil is probably the most insidious, owing largely to the ability of flight. All three
weevils develop as larvae within the grain kernels. They frequently cause almost
complete destruction of grain in elevators or bins, where conditions are favorable and the
grain is undisturbed for some length of time. Infested grain will usually be found heating
at the surface, and it may be damp, sometimes to such an extent that sprouting occurs.
Wheat, corn, macaroni, oats, barley, sorghum, Kaffir seed, and buckwheat are just some
of the grains and products on which these weevils feed.
9. Control
Like all other stored grain products, the most effective way of controlling the infestation
of rice weevil is the prevention of entry to the firm and proper sanitation methods. Proper
sanitation methods include cleaning the stores regularly and between batches, use of pest-
proof containers for storage, separation of infested or potentially infested products from
good quality products etc.

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Temperature control can also be used to control the rice weevil. Freezing infected food
below -17.7°C (0°F) for three days retards the growth and development of various stages
of the insect life cycle. Heating to 60°C (140°F) for 15 minutes destroys all development
stages of rice weevil.
Apart from the above mentioned methods, fumigation, addition of dry ice, use of natural
repellents like bay leaves, cloves and neem, application of insecticides can also be used to
control the damage caused.
10.References
Public Health Vectors and Pests (2013) Rice Weevil [online] Available from:
http://www.kznhealth.gov.za/environ/vector/riceweevil.htm [Accessed on: 05/05/2015]
The Pennsylvania State University (2015) Weevils on Stored Grain [online] Available
from: http://ento.psu.edu/extension/factsheets/weevils-on-stored-grain [Accessed on:
05/05/2015]
Canadian Grain Commission (2013) Rice weevil [online] Available from:
https://www.grainscanada.gc.ca/storage-entrepose/pip-irp/rw-cr-eng.htm [Accessed on:
05/05/2015]