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The head of both weevils extends into a
long thin “beak” at the end of which is its mouthparts. The rice
weevil is further identified by the round or irregularly shaped “pits”
on the top of its thorax. The pits on the granary weevil’s thorax are
oval in shape. Both the rice
and the granary weevil are internal feeders and the larva develops
inside whole grain kernels. The female weevil bores a small hole into
a grain kernel and deposits a single egg into the hole. She seals this
hole with a gelatinous material and then repeats the process on kernel
after kernel until she deposits 300-400 eggs. As a general rule,
however, about 50% of the eggs do not hatch.
The "C" shaped, creamy white,
legless larva emerges from the egg and completes its life feeding
within the kernel. The kernel will eventually be hollowed out and the
larva pupates within. After pupation, the adult beetle remains inside
the kernel for a while before chewing its way out. The open, round
exit holes are sign of a weevil infestation. Weevil exit holes differ
from the exit holes created by the grain moth because they are open.
The moth leaves a little, hinged "lid" over the hole. Within infested
grain, the size of the weevils seen can vary greatly. A weevil’s size
is dependant on the size of the grain kernel in which the larva
developed.
Rice weevils are prolific breeders
and can build up huge populations in stored grain to the point where
the grain has little value as a food product. Infestations located in
storage bins, silos and grain elevators have been found to a depth of
about 5 feet. The grain deeper than that is usually too warm to
support the weevils’ survival.
When disturbed, both types of weevil
"play dead" by drawing their legs close to the body. They then lie
still for several minutes before resuming movement. The granary weevil
does not fly while the rice weevil is an active flier. It often flies
to grain storage bins and buildings from nearby fields and from one
end of a warehouse to the other.
Both rice and granary weevils mainly
attack whole grains, such as wheat, corn, barley and rice. These
weevils may also be found infesting in such foods as macaroni and
spaghetti when they get old. Rice weevils also feed on beans, nuts and
cereals and have been observed sucking the juice from apples and
pears. In homes, infestations are generally found in bird seed, nuts,
decorative Indian corn and, in rare instances, in old pasta stored in
cupboards. The adults feed on the same foods as the larvae but are not
as restricted in their diets because the larvae need to develop inside
whole grains.
The rice and granary weevils are the
most economically significant pests of stored whole grains in the
world. The granary weevil is more common in northern states while the
rice weevil is more prevalent in the southern states. Both beetles,
however, may be found throughout the world. In southern states, adult
rice weevils will overwinter in the fields.
Advice for Rice Weevil:
Use Fortefog P Fumers or
Agrodust.
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