Pantry or stored product pests

Insects that infest our stored foods

Now that the cold weather has arrived we can turn our attention indoors and think about getting rid of those pesky "weevils" and moths that are occasionally found in the kitchen and pantry.

Did you know that insects consume 10-50% of all stored grain worldwide? Most of the loss occurs in commercial storage but a significant amount also happens after consumers take food home and store it improperly. So perhaps we needn't worry so much about producing more food on the farm but should concern ourselves instead with protecting the food we already have in storage!

Here's some basic information about the most common pantry or stored product pests and what you can do about them at home.

Keep in mind the following points: (1) Dry pet food is the most commonly overlooked source of infestations. (2) Do not store items longer than about 2 months unless steps are taken to protect it against infestation (see below). (3) Do not store items in the thin plastic "supermarket" bags because insects can chew through this plastic; use heavy plastic, glass or metal containers instead. (4) Freeze products like birdseed, dry pet food, and flour, before placing them in long-term storage -- freezing can effectively eliminate many insect pests (see below). (5) Discard infested foods when it is found. Trying to salvage food that has become infested with insects is usually not practical and may only provide an ongoing source of infestation.

Weevils - The term "weevil" is often used to describe a wide variety of beetles and true weevils that infest seeds, whole grains, and flour. Some stored-product beetles require whole, unbroken kernels (see photo above) whereas others infest grain meal and flour.

Meal moths - Adult moths are about 5/8" across the wings. Their wings often have a broad, dark band across the back (Indian meal moths). Larvae, "worms", infest a wide variety of foodstuff including grains, dried fruits, seeds, crackers, nuts, powdered milk, dry pet food, and cereals. Webbing produced by larvae is commonly found covering infestations. You may also find moths in the kitchen or other rooms. Meal moth infestations are common in shelled or unshelled nuts, especially walnuts. Spilled pet food is another likely source of infestation.

Flour beetles - A pest of flour, this beetle cannot attack unbroken kernels. Also found in peas, beans, shelled nuts, dried fruits, spices, etc. One generation is completed in 2 to 3 months. You must find all infested foodstuff and dispose of it in order to control this insect.

Dermestid or carpet beetles - There are a number of small beetles that feed on animal hair, hide, and stored food. Dermestid or carpet beetles are notorious scavengers feeding on all manner of dead animal protein. Some of these beetles infest stored food as well. Their presence is often detected when the cast skins of their "fuzzy" larvae are found in kitchen draws or on shelves (see carpet beetle link below for photos).

A word of caution about using insecticides around food

Controlling stored product pests with insecticides is very difficult and usually not recommended because of the proximity of food to the applied poisons. Most of the time stored product pests can be adequately managed with proper sanitation, traps and attention to how packages are sealed and stored. Most importantly, don't store foods longer than about 2 months unless you freeze them first.

If, however, insecticides are used indoors use only the new botanical insecticides, specifically those that are exempt from EPA registration (see the link above for products that are available to homeowners). These insecticides are very effective when used according to their label instructions, much safer for you and the environment, but are somewhat more expensive than conventional pesticides.

How to protect foods with cold treatment

Freezing kills all stages of stored-product pests like moths, beetles and weevils. After cold treatment foods can be removed from the freezer and stored at room temperature in a sealed container. Even packaged foods like flour, dry pet food, dried fruit and so forth can harbor live insects. If these products are placed in storage at room temperature insects will start to multiply resulting in an infestation. On average it takes about 2 months for these infestations to develop. This is why we suggest that you treat food products with cold if you plan to store them longer than about 2 months.

The rules for cold treatment are to keep the package small enough and the time-in-freezer long enough to ensure that the product completely freezes. For example, a five pound bag of flour might take 3-4 days at normal freezer temperature whereas a 1 pound box of raisins might take only 2 days. Freezer times will largely be a guess at first as there are no hard and fast rules. Just remember to keep the package small and time in freezer as long as possible.

Use the links below for specific information about identification, trapping, and control of these stored product pests.

[introduction to different pantry pests]

[biology and control of food-infesting meal moths]

[biology and control of dermestid (carpet) beetles in kitchens]