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PESTS OF STORED FOODS

By: Stephen B. Bambara and Michael Waldvogel, Entomology Extension

Insect Note - ENT/rsc-27

Few pest problems can be more disturbing that to open a bag or box of baked goods and discover that it is infested with insects. There are a number of stored product pests that find their way into items stored on our kitchen or pantry shelves, and it is often difficult, if not impossible, to tell when the item becomes infested. Just because a box "looks" sealed does not mean that insects cannot find their way inside anytime before packaging, during storage in a warehouse, retail store or even in your home. Sometimes, pests show up in places other than a pantry. Regardless of where we find them, the key to solving the problem is to locate the source of the infestation. These insects will often attack any item made of plant material. Typical sources of a problem are items such as:

Common Food Items Attacked Other items attacked
whole or cracked grains (including rice) rodent baits (that contain grain as a feeding attractant)
flour, meal or similar ground grain products
dry pet food
spices
bird seed
cereals grass seed
pasta some powdered soap detergents
candy dried flowers, potpourri, etc.
powdered milk items stuffed with dried beans or other plant material
nuts (whole or pieces) tobacco products

Insect pests that attack stored grains and stored products are usually beetles or moths. With the beetles, both the immatures (larvae) and the adults feed on stored products. In the case of the moths, only the larvae (caterpillars) feed on plant products; the adults either feed on nectar or they may not feed at all. We also categorized these pests by where they feed.

EXTERNAL FEEDERS

These insects feed primarily on the surface of or in cracks on their food source.

(Note: Clicking on the following links will open images that may load slowly over modem connections)

Flour beetles - These small (about 1/5 inch long) reddish-brown beetles feed primarily on flour, meal and other flour-based items. Although they have wings, flour beetles rarely fly.
Signs of an infestation: larvae and/or adults on the infested material; adults crawling on nearby surfaces.

Grain beetles - The beetles are smaller than flour beetles (about 1/8 inch) and brown in color. They are characterized by saw-like margins along the area behind the head. Aside from very slight differences in their appearance, the sawtooth grain beetle (shown at left) does not fly, whereas the merchant grain beetle does. Of the two species, the sawtooth grain beetle is more common.
Signs of an infestation: larvae and/or adults on the infested material; adults crawling on nearby surfaces.

 

Cigarette and Drugstore Beetles - These brownish beetles (about 1/5 inch long) pests are usually found in spices (particularly red pepper), bread, flour, meal, and similar cracked, processed or broken materials. Dry pet foods frequently become infested with these insects. They sometimes infest whole grains, but prefer those that have been broken open. They will eat almost any dried plant material.
Signs of an infestation: larvae and/or adults on the infested material; adults crawling on nearby surfaces.

 

Indianmeal moth - This is the most common stored product pest found in North Carolina. The larvae (immatures) are pinkish-white in color with brownish head capsules. The larvae spin silk webbing over the surface of their food. The adults are small (3/8 inch wingspread) moths with coppery-colored wings. As the larvae finish their development, they often crawl from their food source and onto walls and ceilings.
Signs of an infestation:
larvae or webbing on surface of infested material; larvae or pupae spun into crevices along walls, ceilings, or cupboards; adults flying about the room.

 

INTERNAL FEEDERS

These insects feed inside whole grains.

Weevils - These beetles are about 1/4 inch long and dark brown in color and have a characteristic long snout with chewing mouthparts at the tip. Like grain borers, the female weevil chews a small hole in the grain surface and deposits her egg. The larva tunnels into the grain and feeds on the kernel until it completes its development and pupates inside the kernel. The adult weevil chews its way out of the hollow grain.
Signs of an infestation:
emergence holes in grain; fine sawdust-like frass in bag or on surface; adult beetles crawling around.

Angoumois grain moth - This small (3/8 inch) moth has buff-colored wings. The adult lays its eggs on the surface of the grain. The larva chews its way into the grain and feeds on the kernel before forming a pupal case. The moth pushes its way out.
Signs of an infestation:
emergence holes in grain; fine sawdust-like frass in bag or on surface; moths flying around.

CONTROLLING STORED PRODUCT PESTS
  1. Find the source of the infestation. Start with the list of potential food sources mentioned previously. Never assume that a sealed container means that the contents are not infested. Where do you look? The most obvious place to start is where you see the most insects, usually your kitchen or pantry cabinets, but don't forget other cabinets and drawers in these areas. You also need to look for items that may have spilled or fallen under or behind furniture or appliances, such as your stove, refrigerator or dishwasher. Remember - some of these pests are very mobile either flying or crawling, so don't assume that where you see insects now is always the source of the problem. If you don't find the source of the pest here, then you need to look in other areas, such as:
    • Livingroom, TV room or other areas where food, especially candy or snacks may be eaten.
    • Utility room - look for some other less typical "foods" mentioned above.
    • Attic, basement, crawlspace - besides items that might be stored there, check for bird or rodent nests in these areas, as well as in the chimney. Animal nests containing seeds or plant debris may attract these pests.
    • Attached garage or storage buildings
  1. If the source of the infestation is hard to identify, you (or a pest control professional) can use pheromone traps. These traps contain chemicals that attract the insects. However, because moths are usually very mobile, simply finding moths in an area may not mean that the source is necessarily right there. Areas where insect numbers are greatest are typically near the source.
  2. Discard infested materials. Items which do not appear to be infested, but you think may contain eggs that have not yet hatched can be placed in a freezer for 4-5 days.
  3. Thoroughly clean storage areas, particularly the corners and edges of shelves
  4. Store uninfested items in sealable containers or in the refrigerator.
  5. Practice "FIFO" (First In - First Out), i.e., always use up your oldest materials before opening new packages.
  6. Pesticide applications to storage areas is not necessary if you clean the area thoroughly. However, if you want some added assurance that the problem has been solved, select a chemical that is labeled for use against pantry pests in food storage areas. Before spraying pesticides in a kitchen or pantry, remove all food items (including pet food) and cover all cooking and eating utensils. Allow treated surfaces to dry thoroughly before restocking shelves. Pesticides that can be used in these situations can be found in the NC Agricultural Chemicals Manual .


Pest information and control recommendations presented here were developed for North Carolina and may not be appropriate for other states or regions. Any recommendations for the use of chemicals are included solely as a convenience to the reader and do not imply that insecticides are necessarily the sole or most appropriate method of control. Any mention of brand names or listing of commercial products or services in the publication does not imply endorsements by North Carolina Cooperative Extension nor discrimination against similar products or services. All recommendations for pesticide use were legal at the time of publication, but the status of pesticide registrations and use patterns are subject to change by actions of state and federal regulatory agencies. Individuals who use chemicals are responsible for using these products according to the regulations in their state and to the guidelines on the product label. Before applying any chemical, always obtain current information about its use and read the product label carefully. For assistance, contact the Cooperative Extension Center in your county.

Distributed in furtherance of the acts of Congress of May 8 and June 30, 1914. North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, or disability. In addition, the two Universities welcome all persons without regard to sexual orientation. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.



Last updated - 8/01/00

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