Integrated Pest Management

IPM Manual for Structural Pests in British Columbia

Chapter 6: Stored Product Pests

Learning Objectives

When you have completed this lesson, you should be able to:

1. Describe the importance of identifying stored product pests.
2. Describe the use and placement of pheromone traps for monitoring stored product pests.
3. List three recommendations for household clients to prevent infestations.
4. Describe three measures that prevent stored product pest infestations in commercial accounts.
5. Describe two controls for stored product pests that do not involve the use of pesticides.
6. Describe the use of sorptive dusts in controlling stored product pests.

Identification

Stored product pests infest a wide range of foods including flour, whole grains and seeds, crackers, processed cereals, peas, beans, nuts, dried fruit and spices. Among the common stored product insects in B.C. are:

• saw-toothed grain beetle
• granary weevils
• drugstore beetles
• Indian meal moth
• Mediterranean flour moth

Other stored products pests can also occur in B.C., especially in imported food products:

• confused flour beetle
• larder beetle
• merchant grain beetle
• pea weevil
• rice weevil
• yellow mealworm

Correct identification of stored product pests is important in order to know where to apply treatments. Some insects, such as granary weevils, spend their entire life cycle in the food, therefore control steps can often be limited to disposing of the infested products. Others, such as the Mediterranean flour moth, leave the food when it is time to pupate. They spin cocoons in the corners of cupboards and in cracks, therefore control measures must be planned to take this into account.

There are several key references that provide excellent descriptions and information on life cycles of stored products pests (see list at end of chapter). These should be consulted before planning a pest management program.

Monitoring

Visual Inspections

Storage facilities should be inspected carefully for signs of infestations, inside and outside of the packaging or containers. During the inspection, potential problem areas should also be noted. This includes bins of old or stale products, spilled food and hard to clean areas that could provide refuges for insects.

Ideally, in processing plants, warehouses and retail stores, incoming products should be regularly inspected for signs of pest infestation. This may be done by the pest manager or by someone employed at the facility.

Sampling

Samples of grains and other foods can be drawn from bulk bin or bags and inspected under a microscope for signs of infestations. This is particularly useful for detecting infestations of stored product mites, which are too small to count with the naked eye.

Pheromone Traps

Insect sex pheromones and aggregation pheromones are now available for a variety of stored product pests.

The Indian meal moth lure made in British Columbia, attracts:

• Indian meal moths
• Mediterranean flour moths
• raisin moths
• almond moths, and
• tobacco moths

The pheromones are in lures that can be used in different designs of traps. For stored products moths, the lures are usually placed in delta traps (see figure). Other trap designs are used for stored products beetles, such as sawtoothed grain beetle, the confused flour beetle, and the red flour beetle. The lures can be imported for monitoring as long as the manufacturer makes no claims for their use as a control device. Instructions on the proper placement of lures inside traps are provided with the trap. Always avoid touching the lure when setting out the trap because traces of the pheromone can be spread around the environment, making the trap ineffective.

Pheromone traps should be placed away from doors and windows to avoid attracting insects from outdoors into the building. Traps can be hung from the ceiling of the room or set out on shelves. Trap placement depends on how the building is laid out and where the susceptible food products are stored. In large areas, large numbers of traps can be placed in a grid pattern at intervals of 8 to 15 metres. As catches occur, the grid can be made smaller in infested areas to pinpoint the problem areas. These sources of infestation can then be confirmed by visual inspections.

The beetle lures are generally effective for four to six months and one or two traps is usually all that is required to monitor a site.

Action Decisions

Action should be taken as soon as possible when an infestation is found to ensure that insect populations do not increase in stored products. Records from inspections and other monitoring will enable the pest manager to target areas where infestations have occurred in the past or are most likely to occur.

Prevention

For households, once an infestation is cleaned up (see Control, below), further infestations can be prevented by recommending that clients:

• freeze grains, flour, dried fruit and other dry foods from bulk food stores in the household freezer for a week before transferring the products to cupboards
• store food in insect proof containers of glass or strong plastic with tight-fitting lids, and
• clean kitchen counters and vacuum the insides of cabinets to remove spills and debris

For commercial accounts, the pest manager should recommend sanitation measures, modifying the environment to lower humidity and installation of barriers to prevent infestations.

Sanitation

Maintaining clean conditions is the best control. In warehouses and bulk storage facilities, products should be stored away from walls to make it easy to clean behind the containers. All spills should be cleaned up immediately. Stock should be rotated regularly.

Reduce Humidity

Grains should be stored in a cool dry area. Except for the Mediterranean flour moth which can tolerate very dry conditions, most stored products pests are not likely to be problem in dry conditions, where the relative humidity is below 6%. In commercial facilities, ventilation can be increased to reduce the moisture content of the grain.

Barriers

Insect screens should be installed on ventilators, windows and other openings to keep flying insects out.

Control

Sanitation measures (discussed above), along with a regular monitoring program and thorough visual inspections, usually provide sufficient control of stored product pests. In many instances no pesticides will be needed to achieve good control.

Physical Removal

Destroy infested materials. For some species, such as granary weevils, removing the infested material provides sufficient control as they do not live outside the material.

Heating or Freezing Treatments

Where feasible, extremes of heat or cold can be used to kill insects in infested food. To eliminate an infestation, food products should be kept in a freezer long enough to be frozen at the centre of the container for at least 4 days. Heating to 66°C in an oven for 20 minutes also kills insects. Procedures vary depending on the species of insect and on the type of infested material. Freezing may be a practical control where food storage facilities have large freezers on site and can plan to systematically rotate incoming products through a freezer.

Pheromone Traps

Pheromones can be used to lure insects to an area treated with a spot application of an insecticide. Pheromone traps normally attract more insects to the area than are actually caught on the sticky walls of the trap. Many of the attracted insects land on surrounding surfaces instead of entering the trap.

Under some conditions, pheromone traps may help control Indian meal moth infestations by removing nearly all of the male moths from the population.

Preferred Pesticides

Sorptive Dusts: Diatomaceous earth can be applied to cracks and crevices of storage areas where the pupae and other stages of some stored product species hide. It is not registered for use on, or in, infested food products at this time.

Pyrethrins: Pyrethrins can be applied to equipment motors to kill hiding pests. The ULV jet gun can be used with pyrethrins in storage areas.

Future Controls

Insect Growth Regulators: Methoprene is registered in the U.S. for use against many stored product pests including almond moth, Indian meal moth, lesser grain borer, sawtooth grain beetle, red flour beetle, and confused flour beetle. It is not currently registered in Canada for use on stored products pests, but may be in future.

Other sorptive dusts, such as silica aerogel, are also effective on stored products pest. This is not registered in Canada at this time, but may be available in future.

Other Pesticides

Other pesticides should not be required for most stored products pests. If required in the case of severe or persistent infestations, pesticides must be chosen with careful attention to label directions. Few pesticide products mention stored product pests on their labels. Only pesticides labeled for use in the appropriate areas (e.g., food preparation and storage areas) and for this group of insects (e.g., crawling insects) can be used.

Evaluation

Any treatment program should be followed by visual inspections and other monitoring to assess its effectiveness and to detect new infestations as soon as they appear.

Further Reading

Freeman, P. 1980. Common Insect Pests of Stored Food Products: A Guide to Their Identification. 6th ed. British Museum of Natural History, London. 69 pp.

Mallis, A. 1990. Handbook of Pest Control. 7th ed. Franzak and Foster, Cleveland, OH. 1,152 pp.

Marer, P. J. 1995. Residential, Industrial, and Institutional Pest Control. University of California Statewide IPM Project. Pub. 3334. Oakland, CA. 213 pp.

Olkowski, W., S. Daar and H. Olkowski. 1991. Common-Sense Pest Control. The Taunton Press, Newtown, CT. 715 pp.