Michigan
State University Extension
Home Maintenance And Repair - 01500523
06/24/03
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.
References
Revised by Tom Ellis, M.S., Department of Entomology
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Thomas G. Coon, Director, MSU Extension, East Lansing,MI 48824. This
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