Beetles Identification Guide

Sitophilus granarius (Linnaeus)
granary weevil
calandre des grains
Diagnosis: The species is distinct from S. oryzae in having the hind wings reduced,
the elytral intervals at least as wide as the striae, the strial punctures small
and clearly separated, and the pronotal punctures distinctly elongate.
Sexual dimorphism: Males have the abdominal sterna V and VI distinctly deflected
(Fig. 247), and the rostrum usually wider and less elongate. Females do
not have the abdominal sterna V and VI deflected (Fig. 247), and the rostrum is
usually narrower and more elongate.
Distribution: Throughout the temperate regions. The species is known in Canada
from coast to coast.
Economic importance: This species is a notorious pest of stored grain. In Canada
it causes significant damage primarily in southern Ontario, where it is found in
granaries, grain elevators, and flour mills; in other provinces, the species is encountered
only occasionally. The adults and larvae feed on a wide variety of
grains, and the adults also feed on flour. The eggs are laid beneath the seed coat
in a hole chewed by the females and closed with saliva. The larvae feed on the
endosperm, pass through four instars, and pupate inside the grain. The newly
emerged adult chews its way out of the kernel, leaving a characteristic emergence
hole. Adults are flightless, and the species is restricted to stored grain.
Sitophilus oryzae (Linnaeus)
rice weevil
charançon du riz
Diagnosis: The species differs from S. granarius in having the hind wings fully
developed, the elytral intervals narrower than the striae, the strial punctures large
and nearly contiguous, and the pronotal punctures circular to slightly elongate.
This species is closely related to S. zeamais Motschulsky, another serious
pest of stored grain in tropical, subtropical, and warm temperate regions. Both
species were known under the name S. oryzae until recently. They can be separated
with confidence only by examination of the male genitalia. In S. oryzae the
dorsal surface of the median lobe is evenly convex, whereas in S. zeamais it is
flattened with a longitudinal impression on each side of the middle (Halstead
1963b). Other characters that may be useful for separating these two species
when they occur in mixed infestations include the shape of the pronotal punctures
(usually slightly elongate in S. oryzae, mostly circular in S. zeamais), the
pronotal punctation along the midline (usually absent in S. oryzae and usually
present in S. zeamais), and the size and coloration (smaller and paler in S. oryzae).
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