Michigan State University Extension
Home Maintenance And Repair - 01500524
06/24/03
Grain and Bean Weevils
Several types of weevils, including the rice,
granary, maize and bean/pea weevils, can be encountered
in the home. They are all pests of whole grain foods such
as nuts, beans, cereals, fruits and seeds.
The true weevils (rice, granary and maize weevils)
have a long snout on the head. The rice weevil is about 3
mm long dark reddish brown, with four pale spots on the
upper surface. The rice weevil can fly and is attracted
to lights. The granary weevil is slightly larger (4 mm),
of the same body style and entirely dark chestnut-brown.
It cannot fly and is not attracted to lights. The maize
weevil is also slightly larger than the rice weevil, and
it is very dark reddish-brown or black with four
yellowish spots. All of these weevils infest whole grain
rice, barley, corn, wheat, popcorn, sunflower seeds,
nuts, beans and bird seed. They will also attack hard
cereal products such as macaroni, dry pet food, cereals
and caked flour.
The larvae are white, legless, and feed inside of the
whole kernel or seed - hence they are rarely seen. Weevil
damaged grains typically are hollow and have small, round
emergence holes. The life cycle requires about 4 weeks
and there may be three to five generations per year.
The bean weevils are not true weevils; they are
members of the closely related bean weevil family. Their
body shape is more round than the rice, granary and maize
weevils and they do not have the slender protruding snout
of these true weevils. The common bean weevil is about
1/8 inch (3 mm) long with the upper surface mottled
shades of gray. These feed on dried beans, leaving
perfectly round holes in the beans.
Very often, beans are harvested from the garden which
look perfectly good. However, there can be been weevil
larvae present inside. These larvae can continue to
develop while the beans are in storage, with adults
emerging during winter. Many a housekeeper has been
dismayed to find a good supply of beans ruined by this
insect. Heating the beans to 130 degrees F for 1/2 hour
prior to storage will kill any larvae present and arrest
any further development. A small number of dried larvae
in the beans does not constitute any hazard to health.
Integrated Pantry Weevil Management
Purchase susceptible foodstuffs in quantities that
can be used in a short time: 2-4 months, if possible.
When purchasing packaged food, be certain the containers
are not broken or unsealed and that there are no signs of
infestation. Check the packages for freshness dates. Once
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 insect development. Keep
food storage and preparation areas clean at all times;
spilled and exposed food attracts insects.
If granary, rice or maize weevils are found in the
kitchen, a search of all possible food sources should
uncover the source of infestation. Disposal of infested
grains and a thorough cleanup of the area should
eliminate them.
For bean weevil control, all that is required is to
remove the infested beans and clean up the storage area.
This pest does not infest as wide a range of stored goods
and an insecticide is not recommended.
For a complete listing of suggested control options
for all home, yard and garden insect pests contact your
local Extension Service, found under local government in
the phone book.
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.
Revised by Tom Ellis, M.S., Department of Entomology
This information is for educational purposes only. References
to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU
Extension. Reprinting cannot be used to endorse or advertise
a commercial product or company.
MSU is an affirmative-action, equal-opportunity employer. Michigan State
University Extension programs and materials are open to all without regard to race,
color, national origin, gender, gender identity, religion, age, height, weight, disability,
political beliefs, sexual orientation, marital status, family status or veteran status.
Issued in furtherance of MSU Extension work, acts of May 8 and June 30, 1914, in
cooperation with the U.S. Department of Agriculture. Thomas G. Coon, Director,
MSU Extension, East Lansing,MI 48824. This information is for educational
purposes only. Reference to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not mentioned.
This file was generated from data base 02 on 02/04/08.
Data base 02 was last revised on 06/24/03.
For more information about this data base or its contents please contact
strausc@msu.edu .