Properly Identifying Stored Product Pest Doppelgangers

Editor's note: This article originally appeared in the Nov./Dec. print issue of QA Magazine under the headline "Stored Product Pest Doppelgangers."

These types of stored product pests may not be as easy to differentiate from the more common stored product pest insects and, unless carefully examined, may be recorded and misidentified as the wrong pest. This can lead to an exhaustive inspection seeking the source of a pest of mistaken identity. Several of these insects are in the same family, and so the ease to which they are misidentified is understandable.

HAIRY FUNGUS VS. CIGARETTE AND WAREHOUSE BEETLES. Both the cigarette (Lasioderma serricorne) and warehouse beetle (Trogoderma variable) are common stored product pests. There is another beetle, the hairy fungus beetle (Typhaea stercorea), that on occasion can also be found in food facilities. It is more often associated with either grain in poor condition, corn fields, grain stored in grain bins or, seasonally, a cued entrance from the outside environment.

When we view close-up pictures of these pest look-alikes, it is fairly easy to see some of the differences, but when insects are viewed in an insect light trap, they will appear as similar, small, oval, reddish brown beetles that are hard to distinguish. They will range in the 1/10- to 1/8-inch range, and the magnification of specimens will be required.

In separating the cigarette beetle from the hairy fungus beetle, we need to look at the antennae. The antennae of the hairy fungus beetle is clubbed with the last three segments enlarged. The antennae of the cigarette beetle does not end in an enlarged club, and the segments are more uniform in shape. In addition, the segments on the cigarette beetle’s antennae are triangular and look like the teeth of a saw.

The warehouse beetle will have variable patterning on the wings, and the antennae will be much shorter than that of the cigarette beetle or hairy fungus beetle. The patterned wings of the warehouse beetle will be the most noticeable characteristic used to separate this pest.

It is always important to carry a hand lens or use another form of magnification for ensuring the correct ID. Collect and preserve specimens and get help from an expert when necessary. Lastly, use data from pheromone traps when they are available.

Although hairy fungus beetles are light trap attracted, they won’t be attracted to the cigarette beetle or warehouse beetle pheromone lures in traps. A comparison on light trap captures versus pheromone trap data will provide a clue that further examination of the light trap captures is needed. If you are capturing this cigarette beetle look-alike in a light trap but not a cigarette beetle pheromone trap, double check the ID. What you believe is a cigarette beetle may be a fungus beetle.

FOREIGN GRAIN VS. RED FLOUR BEETLE. Our next set of beetles are the foreign grain beetle (Ahasverus advena) and red flour beetle (Tribolium castaneum). Size is the main differentiating factor. The foreign grain beetle is 1/12 of an inch, while the red flour beetle averages 1/8 inch. The foreign grain beetle has a pair of round projections or lobes at the corner of the thorax or area behind the head. Both have three clubbed antennae, are reddish brown in color and have an elongated body. Magnification will be required to see the corner lobes on the foreign grain beetle.

Behaviorally, the foreign grain beetle is more seasonally active, entering structures late summer and fall. Exclusion becomes an important part of preventing these pests. They are extremely light attracted and may be found in huge numbers in insect light traps.

Foreign grain beetles will also differ in their food choices. They will feed on mold and grain in poor condition and although they may enter a food facility are not likely to infest the food inside. Red flour beetles will feed on flour, flour-based products and other grain-based foods. They are a main pest of flour mills and facilities that process and store flour and flour-based foods.