A manual of rice seed health testing - IRRI books - International Rice ...

Rice weeviI
Scientific name: Sitophilus oryzae
(Linnaeus)
Common name: rice weevil
Quarantine status: primary pest; can
infest rice in the field
Stage of entrance or attachment to
seed: egg, larva, pupa, or adult
The adult rice weevil is a 2.5-4-mm
long reddish brown to brown-black
beetle, and can be confused with the
maize weevil. Its diagnostic features
are densely rounded or irregularly
shaped punctures on the prothorax;
a long narrow snout with eightsegmented,
elbowed, or club-shaped
antennae on the head; and hard front
wings with four reddish brown
spots. The adult lives 7-8 mo.
Each female lays 300-500 eggs singly
in holes chewed in seeds. The
single larva hollows out cach seed.
The larvae are grublike, white, legless,
have brown heads, and the
lower side of the body is straight.
The life cycle is 4-7 wk.
The newly formed adult chews its
way out of the grain, leaving a round
hole. The adult rarely flies, prefers
smaller grains, and its feeding causes
irregularly shaped holes. When disturbed,
the adult feigns death by
drawing its legs close to its body,
falling, and remaining motionless for
several minutes.
Grains with closed lemma and
palea are resistant to entry by this
weevil.
Maize weevil
Scientlfic name: Sitophilus zeamais
Motschulsky
Common name: maize weevil
Quarantine status: primary pest; can
infest grain in the field
Stage of entrance or attachment to
seed: egg, larva, pupa, adult
The adult has a 3-5-mm long, brownblack
to reddish-brown body and
may be confused with the rice weevil.
Its diagnostic features are
densely rounded or irregularly
shaped punctures on the prothorax,
a long narrow snout on the head,
clubbed or elbow-shaped antennae
with eight segments, and hard front
wings with four reddish-brown
spots. The adult lives 4-5 mo.
The maize weevil is larger than
the rice weevil, although both have
hindwings. The adult is a strong
flier, and prefers larger grains.
Sitophilus oryzae and S. zeamais can
only be differentiated by the internal
character of the male aedeagus. The
aedeagus of S. zeamais is flat and has
two distinct impressions. That of S.
oryzae has an even, convex upper
surface. Females of the two species
appear very similar.
Each female lays 100-150 eggs singly
in holes chewed in seeds. The
larva hollows out each seed. The
larva is grublike, white, legless, has a
brown head, and the lower side of its
body is straight. The life cycle is
5-7 wk.
Angoumois grain moth
Scientific name: Sitotroga cerealella
(Olivier)
Common name: Angoumois grain moth
(named after the French province
which experienced an outbreak of the
moth in 1760)
Quarantine status: primary pest; can
infest grain in fields and storage
Stage of entrance or attachment to
seed: larva, pupa
The moth's body is 5-10 mm long
and yellow-brown with several black
dots on the forewing. It may be confused
with the white-shouldered
house moth Endrosis sarcitrella
Linnaeus. The Angoumois grain
moth's diagnostic features include
pointed wing tips; a black spot beyond
the center of the upper side of
the front wing; very elongated,
sharply pointed, and needlelike apex
of the hindwing; fringed wings; and
curved labial palp. Adults live
10-30 d.
Each female lays 30-150 cggs singly
or in clumps on the surface of
grain. Each larva hollows out the inside
of one grain. Larvae are yellowwhite
with dark heads. Their life cycle
is 5-6 wk or as long as 12-13 wk
when exposed to low temperatures.
After emerging from the grain,
the adult leaves a trap door. Adults
prefer whole grains to milled rice.
The infested grain has a small round
opening in it. The Angoumois grain
moth has a climatic plasticity index
of 550. The moth dies at temperatures
below 10 °C; eggs and larvae
die when temperatures exceed 60 °C.
72 Rice seed health testing manual