Pheromone finesse

|  May 1, 2003

Stored food insects communicate with each other using different types of pheromones. It is common practice to monitor food storage areas and food manufacturing facilities with traps using lures containing these compounds. However, the decision to use pheromones for monitoring stored food insects is often based on a pest management professional’s level of knowledge about their use. For many, it is still an untried or misunderstood technology that has been available for more than 20 years.

To successfully use these devices, we must work with four elements that have a significant influence on trapping results:

  • the pest
  • the pheromone lure
  • the trap type
  • the location or placement of the trap

Start with the pest

The starting point and most important element to understand is the insect. The biology and behavior of each species limits the choices and placement of trapping systems.

For example, the red flour beetle (Tribolium castaneum), confused flour beetle (T. confusum), saw-toothed grain beetle (Oryzaephilus surinamensis), merchant grain beetle (O. mercator), rice weevil (Sitophilus oryzae), maize weevil (S. zeamais) and granary weevil (S. granarius) are insects that predominately crawl from one food source to another. The red flour beetle, merchant grain beetle, rice weevil and maize weevil can fly, but rarely indoors. To monitor these pests in large facilities:

1. Do not use hanging traps to capture crawling stored food beetles that rarely fly. Instead, use pitfall traps. Sticky blunder traps can also be useful.

2. Weevils and grain beetles are more mobile than flour beetles. Place traps for flour beetles 10 to 15 ft. apart, and up to 20 ft. for the other species.

3. Flour beetles are more active in the dark, and occur in patches near food and harborage. Traps should be in more secluded, undisturbed areas such as corners, behind posts, under shelves, gondolas, at the base of racking systems, near cracks and crevices and in dimly lighted areas where food accumulates.

4. Grain beetles are more mobile, but tend to follow crevices and edges. Place more traps accordingly to these sites.

5. Weevils are the most mobile when searching for food and can spread in all directions so traps can be more widely placed (like 20 ft.).

6. Beetle traps should be in targeted locations, such as near food storage and harborage sites or areas of high risk to infestation. Standard grid placement (such as every 15 sq. ft. throughout a building) results in many traps with poor catch. Better time can be spent on traps with a high chance of capturing insects.

Harnessing pheromone effectiveness

Both sexes of the flour beetles, grain beetles and weevils are attracted to aggregation pheromones and food odors (kairomones). Some traps, for example, use a no-spill gelled oil food attractant combined with aggregation pheromones of flour beetles (among several other species). Dome-style traps use food oil attractants and separate pheromone lures for flour beetle. The dome is a good cover for dusty areas. A new floor trap my company has developed only uses a food attractant, but the trap keeps the captured beetles alive, thus allowing natural pheromone to be emitted from the beetles in the trap. It seems to be especially effective with grain beetles.

Unfortunately, there is no commercial pheromone for the saw-toothed and merchant grain beetles available yet. The weevils seem to be caught easily in any of the traps. Some weevil pheromones are available and can improve catch compared to food attractants only. Flour beetles are more selective, based on pheromone concentration and trap design/placement. In places where competing food is available (like flour), the trap catch can be dramatically less. Sanitation improves catch, as the beetles are more starved and need to search further. To monitor for pests in food product or for locating structural infestations:

1. Use traps best suited to the target beetles.

2. Use lure/food combinations that are most attractive to the target beetles.

3. Place traps in covered stations if necessary for dust and people protection. Flour beetles are very poor climbers, and the covered station may prevent access to the traps. Choose a design that has holes flush to the floor.

4. Map your traps so that you can account for them. Lost traps mean no data – and possibly problems if they end up in the “food channel.”

For the more active crowd . . .

Cigarette beetles (Lasioderma serricorne), drugstore beetles (Stegobium paniceum) and warehouse beetles (Trogoderma variabile) are much more active. They are good fliers, can be found outdoors as well as indoors in the southern states and are attracted to light. The females produce sex pheromones, which unlike aggregation pheromones attract only the male beetles and can be detected from more than 25 ft. Presently, the pheromone for drugstore beetles is limited in the United States.


Cigarette and drugstore beetles will fly when the temperature is above 70° F, while warehouse beetles fly when it is above 65° F. For these beetles:

1. Use sticky hanging traps like diamond, delta and wing traps with a good pheromone lure for monitoring large warehouses.

2. Flat sticky traps with lures and floor traps can be used for smaller areas like grocery stores and residential kitchens.

3. Replace lures according to manufacturer instructions (four to 12 weeks, depending on type).

4. Date your traps to indicate when the lure was installed.

5. Remove beetles from the traps so you can count new beetles accurately.

6. Replace traps if they are 50% filled or more.

7. Do not place traps with these pheromones within 30 ft. of an outside door or exterior window, to reduce the opportunity of immigration from outside.

8. Document the number of newly caught beetles on a separate record/report.

9. Adding a sex pheromone lure to a light trap can attract males and females to the glue traps.

10. Using pheromone traps in a trap line outdoors about 50 ft. away can monitor the outdoor population and indicate whether indoor catches are from beetles entering the facility from outside.

The data you collect can help you understand the dynamics or origin of a population inside a commercial facility, or even a residence. The best way to learn how to use these systems is to try them in one account on a small scale. Let the customer know what you are doing and what you can expect to gain in terms of timely or reduced pesticide applications.

You can also evaluate the effectiveness of your pest management program by looking at the numbers. Gathering this data is a way of gaining knowledge and experience. Before long, you will be comfortable with their use and know what to expect.

Alain VanRyckeghem is the technical director of Insects Limited, Inc., Westfield, IN. He was a college professor for 12 years in a two-year, pest management technician program in Lindsay, ON, and presently does training, entomological research and pheromone synthesis for stored food insects. Contact him at

This article is tagged with and posted in Rice Weevil, Stored Product Pests

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