Agriculture and Agri-Food Canada Insect Identification Sheet No.
80 March 1981
The granary weevil, which is found throughout the world, attacks
all small grains and hard cereal products such as macaroni. In
Canada, it is somearial found in prairie grain elevators, but is
more common in farm storage areas in southern Ontario.
feed on the kernels, leaving only the hulls, and a severe infestation
can reduce stored grain to a mass of hulls and frass. They often
prepare the way for other insect species that feed on damaged
kernels but are unable to penetrate sound grain. In addition,
the feeding weevils contribute to grain heating and further damage.
The adult is a polished chestnut brown or blackish
beetle about 5 mm long, with a head that is prolonged into a long,
slender snout. The adults, which are unable to fly, live for 7
to 8 months and during this period each female lays about 150 eggs.
In egg-laying, the female drills a small hole in the kernel, deposits
an egg in the cavity and seals the hole with a gelatinous secretion.
There is only one larva in each infested kernel. The white, legless
grub completes its growth, pupates and develops into an adult weevil
within the kernel. After reaching the adult stage, it eats its
way out of the kernel. In summer, the life cycle may be completed
in 4 weeks. Infestation can start at temperatures as low as 15
degrees but optimum development takes place at about 30 degrees
and at a relative humidity of 70%.
weevils can spread in grain residues. Because most of the insect's
life cycle occurs inside the kernel, an initial infestation is
difficult to detect. A heavy infestation can be treated with
an approved fumigant or, in winter by cooling the grain to a
temperature of -7 degrees and holding this temperature for at
least 6 weeks. Consult your provincial agricultural representative
for full details on controlling the pest.