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Sawtoothed Grain Beetle And Merchant Grain Beetle

Sawtoothed Grain Beetle And Merchant Grain Beetle

Open Integrated Pest Management Education Resource

Sawtoothed Grain Beetle

(Oryzaephilus surinamensis) and

Merchant Grain Beetle

(Oryzaephilus mercator)

Integrated Pest Management Plan

Sawtoothed Grain Beetle (Oryzaephilus surinamensis) and Merchant Grain Beetle (Oryzaephilus mercator) Integrated Pest Management Plan

This document contains information about the biology and management of the Sawtoothed and Merchant grain beetles. A range of management options is listed. From this list, the IPM Practitioner can choose options to develop a unique management plan for each particular customer site.

General Information

Management Objectives for the Pest at the Particular Site

What do you want/need to accomplish at the site in regard to the grain beetles?

The answer to this question will vary, depending on the site and the customer. Some examples are:

  • Prevent or minimize grain beetle damage to food.
  • Eliminate grain beetles from the site.
  • Help the customer comply with Health Department regulations.

Sawtoothed and Merchant Grain Beetle Identification

  • These 2 beetles are difficult to tell apart.
  • They are both flattened, reddish brown, and about 1/10” long.
  • They both have 6 sawtooth-like projections on the side of the thorax.
  • Under magnification, differences in the antennae, head, and eyes can be seen.
  • Eggs, larvae, and pupae of these 2 beetles are similar.
  • Mature larvae are yellowish white and less than 1/8” long. The larvae have brown heads and 3 pairs of legs.
  • The pupal case is made out of particles of food glued together.

Why the Sawtoothed and Merchant Grain Beetle are Considered Pests

  • The larvae and adults of these beetles feed on a wide variety of stored food products.
  • They contaminate far more food than they actually consume.
  • Many people are unnerved by the thought or actual presence of insects in their food

Special Regulatory Conditions

California Health and Safety Code Sections that relate to cleanliness in food establishments:

114010. “All food shall be prepared, stored, displayed, dispensed, placed, transported, sold, and served as to be protected from dirt, vermin, unnecessary handling, droplet contamination, overhead leakage, or other contamination.”

114030. “A food facility shall at all times be so constructed, equipped, maintained, and operated as to prevent the entrance and harborage of animals, birds, and vermin, including, but not limited to, rodents and insects.”

114040. “The premises of each food facility shall be kept clean and free of litter, rubbish, and vermin.”

114050. “All food facilities and all equipment, utensils, and facilities shall be kept clean, fully operative, and in good repair.”

Biology and Behavior of the Sawtoothed and Merchant Grain Beetle

To be successful, management strategies must take into consideration the biology and behavior of the pest. Understanding the biology of a pest can reveal weaknesses and vulnerabilities that can be exploited when trying to manage the pest.

General Biology

  • Grain beetles go through 4 distinct stages of growth: egg, larva, pupa, and adult.
  • The adult females lay an average of 200 to 300 tiny white eggs singly or in batches in the larval food.
  • The larvae feed and when mature, make a pupal case out of particles of food glued together with an oral secretion.
  • Inside the pupal case, the larva transforms into an adult.
  • The sawtoothed grain beetle completes its life cycle in about 1½ months.
  • The merchant grain beetle completes its life cycle in a little over a month.

Feeding Behavior

  • These beetles are capable of chewing through paper, cardboard boxes, cellophane, plastic, and foil.
  • Larvae and adults of both species feed on
    • All kinds of grain products such as meal, flour, cornstarch, cereals, pasta, bread, and crackers
    • Nuts and seeds, including bird seed
    • Dries herbs and spices
    • Dry pet foods
    • Dried fruits
    • Chocolate
    • Sugar
    • Dried meats
    • Drugs

Factors that Favor Grain Beetles

  • Improper storage of food products that leaves these materials vulnerable to infestation
  • Failure to inspect food products and their packaging before storing
  • Storing food items for lengthy periods of time
  • Poor sanitation in food storage areas

Monitoring and Record Keeping

The purpose of monitoring is to track pest activity in order to catch small problems before they become overwhelming. Monitoring makes it possible to pinpoint pest activity so treatments can be targeted. Monitoring also makes it possible to properly time pest management actions and to evaluate the effectiveness of those actions. Records are kept to document the methods and products used and to record information that can be used to fine-tune pest management methods and plan future actions.

A commercially available sticky trap that is baited with a pheromone will capture male beetles. This can be used to monitor for the presence of this pest.

Supplies should be stored up off the floor on pallets or shelves and away from the wall at least 18” to allow for thorough inspections.

Tolerance Level


The “tolerance level” is the number of beetles that triggers action to control the pest. The tolerance level is site-specific and differs depending on the customer, the location, and other factors. Determining the tolerance levels for a site helps prioritize work that must be done to control the pest.

Management Strategies


Management of grain beetles is largely a matter of sanitation. Heat and cold can be used to kill the insects directly.

Habitat Modification


To limit availability of food

  • Immediately clean up and dispose any spilled grains, grain products, flour, or other items attractive to stored product pests. This is important in storage areas as well as loading docks and other transportation areas.
  • Keep food storage areas clean. This includes areas where pet food or birdseed is stored. Regularly vacuum shelves, floors, baseboards, etc. to remove whole grains, grain fragments, flour, seeds, crumbs, and other debris. Pay careful attention to all cracks and crevices.
  • Thoroughly clean food preparation and eating areas daily, paying special attention to crumbs and other susceptible foods that may fall behind or under appliances or into cracks and crevices in workspaces.
  • Dispose of or treat (see below) infested items immediately.
  • Throw away or treat (see below) infested decorative items.
  • Store food products in insect-proof containers, such as metal, glass, or heavy plastic. The containers must have tight-fitting lids, preferably with rubber gaskets. This is especially important once packages are opened; however, these beetles can chew through paper, cardboard, foil, cellophane, and plastic, so unopened packages may not be pest-proof.
  • Store food items in a cool, dry location.
  • Date incoming supplies and use the oldest first.
  • Buy supplies in quantities that can easily be used in less than 2 or 3 months, unless they can and will be stored in a freezer.

To limit shelter/harborage

  • Inspect incoming supplies:
  • Check packages for damage and a tight seal
  • Check package due date for freshness
  • Check packages for insect evidence such as webbing or cocoons
  • Remove food packages from their cardboard shipping containers before storing, to eliminate hiding places.
  • Caulk or otherwise seal cracks and crevices in food storage areas, in cabinets, walls, floors, baseboards, etc.

Physical Controls

Physical controls employ physical means to remove beetles from the structure or to kill them directly.

  • Vacuum regularly to remove potential food, infested material, and stray insects
  • Treat infested materials with cold or heat. Spread material in shallow pans to make sure all of it is thoroughly heated or cooled:
  • 4 to 7 days in a freezer at 0°F
  • 5 minutes in a microwave
  • 2 to 3 hours in an oven at 120°F to 130°F
  • At 180°F, death is rapid
  • Heat treat dried fruits or vegetables by placing them in a cheesecloth bag and dipping in boiling water for 6 to 10 seconds
  • Pheromone traps can be used for monitoring and pinpointing the infestation, but not control.

Chemical Controls

Chemical controls are not recommended for grain beetles.

The IPM Partnership

The PCO-Customer Partnership is Very Important

IPM works best when the customer and Pestec form a partnership to tackle the pest problem. Grain beetles cannot be managed satisfactorily without the cooperation of the customer, especially in the area of sanitation. Pestec will discuss the findings of the initial inspection and any subsequent monitoring sessions with the customer to determine which issues and tasks will be the responsibility of Pestec and which will be the responsibility of the customer.


Information is a powerful tool in IPM. Information can help change people’s behavior, particularly in how they store food and dispose of waste. Changing these behaviors is a necessary part of managing stored product pests. Occupants of buildings and homeowners can also help in the early detection of pests so that Pestec can be alerted before the problem is severe.

Pestec’s highly trained and knowledgeable staff can provide pest management education or training sessions for facilities managers, risk managers, building occupants, homeowner associations, and others.