Grain and Flour Beetles
There are three common beetles that infest stored
grains, flour, cake mixes and other flour products. These
are the saw-toothed grain beetle, the red flour beetle
and the confused flour beetle. All life stages of these
"bran bugs" can be found directly in the food they
infest. Infestations are usually discovered when an
infested package is opened for use, or when small brown
beetles are discovered in the kitchen near containers of
stored grain products.
The sawtoothed grain beetle is about 1/8" (3mm) long,
dark brownish-red, and has six saw-like teeth on each
side of the prothorax, the body segment behind the head.
The larvae are very small (less than 1/4 inch), yellowish
-white and worm-like. Both the beetles and larvae feed on
flour, grains, cereals, shelled nuts, bread, dried
fruits, macaroni, spices, candy, sugar and other stored
products. The small size and flattened shape of the
beetles enable them to enter poorly sealed packages.
The complete life cycle (egg to adult) may occur in
40 to 60 days. There may be up to six generations per
year. The adults live for an average of 6-10 months but
can live as long as 3 years.
The confused flour beetle and the red flour beetle,
are serious pests of milled and processed grains,
especially flour. They may also infest beans, peas,
dried fruits, shelled nuts, chocolate, spices and
tobacco. Adult flour beetles are small (1/7 inch),
reddish-brown and have a smooth-sided thorax. They are
shinier and more convex than the sawtooth grain beetles.
The red and confused flour beetles look very similar,
differing primarily in the shape of their antennae. The
larvae are yellowish-white, worm-like, and have a two
pointed structure on the tail end.
The life cycle (egg to adult) generally takes 6-8
weeks. There may be up to 5 generations per year. Adults
generally live for a year.
A fourth grain beetle sometimes found in Michigan
homes is the foreign grain beetle. It looks somewhat
similar to the saw-toothed grain beetle, except it lacks
the saw-teeth on the side of the prothorax. Surprisingly,
this grain beetle is not usually found in stored grains.
It is more commonly encountered feeding on molds growing
on moist grain, and in new houses on new cabinets made of
particle board. The particle board, when new, may still
be damp and mold may grow on the plant materials used in
its construction. These beetles can live on this and are
often quite common around bathroom vanities and kitchen
cupboards. So far, we have no seen this beetle infesting
stored products, but given the proper conditions, it
could do so.
Integrated Grain & Flour Beetle Management
Purchase susceptible foodstuffs in quantities that
can be used in a short time: less than 2-4 months, if
possible. When purchasing packaged food, be certain the
containers are not broken or unsealed. Check the packages
for freshness dates. Once the food is in the home, use
older packages before newer ones, and opened ones before
unopened ones. Storing dried foods in a freezer will
prevent pest development. Keep food storage and
preparation areas clean at all times; spilled and
exposed food attracts insects.
(1) To control grain and flour beetles, start with a
thorough check of all stored foodstuffs. Once the
infested materials are found, discard any that are
thoroughly infested. Check for open pet food bags for
infestation. Check for open dry pet food, these can
harbor the beetles.
(2) While all stages of these insects can be killed
with heat (130 degrees for 30 minutes), the risk of
releasing large numbers of insects during the heat
treatment process makes this tactic questionable. The
beetles can be killed in packages by placing the items in
a freezer for 3-4 days. However, there is no easy way to
separate the insects from the food once they are killed.
(3) Contents from all packages (opened or unopened)
which appear to be uninfested should be transferred to
glass or plastic containers with tight-fitting lids. It
is possible that eggs were laid in these products and
that they may hatch later and lead to an infestation if
not contained. Boxes, plastic bags and paper bags cannot
be sealed tightly enough to exclude these pests. Glass
containers make periodic examination of the food easier.
(4) Remove all food, food containers and utensils
from the infested areas and clean thoroughly, first with
a vacuum cleaner and then with soapy water. Special
attention should be paid to cracks, crevices and corners
(including under and behind appliances) were bits of
flour, meal or other food may have accumulated.
(5) We do not recommend using an insecticide.
(6) Continue to observe the area for several months
after treatment. If beetles reappear, the cleanup may
have been inadequate or infested packages may have been
brought into the home.
For a complete listing of suggested control options
for a for all home, yard and garden insect pests see:
Michigan Insect Pest Management Guide, 1991.
Publication like this are available from your local
Extension Service. Read and follow instructions on the
pesticide label. Heed all warnings. Check with your
physician if you have any concerns regarding your
personal health risk.