Warehouse Beetles Cause Big Damage

June 1, 2000

Warehouse beetles attack more kinds of stored foods than any other insect but can be controlled through good sanitation, inspections and an effective insecticidal program.

The warehouse beetle is one of the major stored food pests in the United States. Its distribution is throughout the U.S., except possibly Alaska. This beetle has a wide range of foods, including dead insects, and it attacks more kinds of stored foods than any other insect. It is found in manufacturing plants, warehouses, retail stores and occasionally in homes. Warehouse beetles prefer foods high in protein. Therefore, facilities where powdered milk, dehydrated egg and other dried-protein products are either produced or used are likely candidates for an infestation. However, the insect can be controlled through good sanitation practices, which may include inspections and an effective insecticidal program.

A light infestation occurs in areas where the beetles cannot contaminate food like electrical panels, cracks and crevices, vacuum cleaner bags, etc. A light infestation can become explosive if appropriate precautions are not taken. Precautions include the inspection of incoming raw materials and regular inspections of light and pheromone traps and glueboards. I was involved in two cases where the entire facility was fumigated with methyl bromide because of a heavy infestation. In another case, a pasta company had to destroy more than a million dollars worth of warehouse beetle-infested products. This insect is also included in the Food and Drug Administration’s HACCP (Hazard Analysis and Critical Control Points) program.

THE LIFE CYCLE. The larval color varies in its early development from yellowish-brown, to brown and brownish-black as the larva matures. The larva length is about ¼-inch long with many hairs on the body. The adult beetle is about 1/8-inch long, brownish-black in color with a yellowish-orange color pattern on the hard wing covers. The adults are fairly good fliers. I believe that most infestations occur as a result of adult beetles flying into a facility while doors are open. When it becomes dark outside or if it is too windy, the flights stop. Flights may occur inside a warm building even if it is dark outside. The life cycle from egg to adult is about six weeks and a female may lay up to 94 eggs in an infested food source. A larva under unfavorable conditions (no food or temperatures less than 40 degrees) may transition into a diapause stage. Larva in diapause may survive up to three years or longer.

When larvae of the warehouse beetle are ingested, a person may become ill. The first symptom is abdominal pain that may last one to two days. This is followed by vomiting and/or diarrhea. Dogs also can get ill after eating a dry pet food infested with larvae.

The insect most involved with complaints and litigation is the Indian-meal moth, followed by the warehouse beetle. Between the two insects, the latter is more frequently found infesting food plants. If sanitarians are not familiar with this insect, a light infestation may be overlooked.

Indian-meal moths, followed by warehouse and cigarette beetles, cause most package damage to products. Indian-meal moth infestations usually occur at distribution centers and retail food stores while a warehouse beetle infestation may occur at the manufacturing level and in distribution centers.

BEETLE ID. The two most encountered Trogoderma species on foods in the United States (except Hawaii) are the warehouse beetle and the larger cabinet beetle. In Hawaii, the Hawaiian cabinet beetle is the most predominant species and is a major pest associated with food infestations and is readily attracted to a pheromone lure. The other five species can be classified as minor pests.

To identify Trogoderma beetles by using the wing color patterns would be difficult if one is not familiar with the pattern variation. Warehouse beetles have more than 12 color patterns. Examination of the male genitalia under a microscope is the most accurate method for the species ID.

To study the genitalia of beetles collected in the pheromone trap glue is time consuming and difficult. Therefore, I put together a 15-inch plastic tube with 1/8-inch perforated holes around half of the tube. The bottom screw cap contained 70 percent rubbing alcohol. Trogoderma sex pheromone produced by Consep was placed inside the tube from the top. The attracted Trogoderma fell into the alcohol (this kept them soft and pliable for microscopic dissection). All seven species (excluding the Hawaiian cabinet beetle) were collected using this tube. To me, there’s no doubt that if this experiment were performed in Hawaii, the result would be the same. The sex pheromone collected only males (except for the plain cabinet beetle, when a single female was collected in each of the experiments).

The author is the former chief of laboratory services, California Department of Food and Agriculture. He can be reached via e-mail at gokumura@pctonline.com.


Sweet Sixteen

Here’s a list of the 16 Trogoderma species in the United States:

Trogoderma angustum (Solier)

Trogoderma anthrenoides (Sharp)

Trogoderma ballfinchae Beal

Trogoderma fasciferum Blatchley

Trogoderma glabrum (Herbst)

Trogoderma grassmani Beal

Trogoderma inclusum (LeConte)

Trogoderma okumurai (Beal)

Trogoderma ornatum (Say)

Trogoderma paralia Beal

Trogoderma primum (Jayne)

Trogoderma simplex Jayne

Trogoderma sinistrum Fall

Trogoderma sternale Jayne

Trogoderma teukton Beal

Trogoderma variabile Ballion

Note: Trogoderma granarium (Everts), commonly known as the khapra beetle, was not listed because this species is eliminated in the United States. However, this quarantine beetle is still intercepted at U.S. ports on foreign ships.


The following Trogoderma beetles have been caught in pheromone traps and are associated with stored foods:

Trogoderma anthrenoides — Hawaiian cabinet beetle

Trogoderma glabrum — glabrous cabinet beetle

Trogoderma grassmani — tiny cabinet beetle

Trogoderma inclusum — larger cabinet beetle

Trogoderma ornatum — ornate cabinet beetle

Trogoderma simplex — plain cabinet beetle

Trogoderma sternale — western cabinet beetle

Trogoderma variabile — warehouse beetle

Note: Since three of the above species did not have common names, the author has assigned Hawaiian cabinet beetle to T. anthrenoides; tiny cabinet beetle to T. grassmani; and western cabinet beetle to T. sternale.