Confused Flour Beetle

Tribolium confusum

These insects, also called bran bugs, are common pests of flour. They may infest any product made with grain, but they cannot infest sound (undamaged) grain. Flour beetles require about a month to complete their life cycle. Adults may live up to three years.

The adult confused flour beetle can enter holes in packaging that are less than 1.35 mm in diameter (Cline and Highland 1981).

Confused Flour Beetle

Confused Flour Beetle

*Courtesy Insects Limited, Inc.
Why does it matter?
Stored-product insects, such as the Indian Meal Moth and Confused Flour Beetle can work their way into any package, including foils and plastic films. National and Global distribution channels present food contamination risks that can be mitigated with this technology. Insect infested products lead to consumer complaints, inventory returns, retail charge-back, and lost sales opportunities for consumer goods companies. The combination of these risks creates a cost savings opportunity.Download the full PDF.

What is the Confused Flour Beetle?

The confused flour beetle, Tribolium confusum Jacquelin du Val, is a common insect that attacks stored grains and foods in the pantry. This insect has a world wide distribution and is very abundant in the United States. It generally feeds on finely ground or broken starch materials, such as flour or meal. Adults and larvae feed on broken kernels and fine-grind materials in granaries, mills, warehouses, and other places where grain or grain products are stored. A closely related species, the red flour beetle, Tribolium castaneum (Herbst), is often found associated with the confused flour beetle. These two species are difficult to distinguish, particularly in the larval stage of development.

What is the Confused Flour Beetle life cycle?

The adult beetles are very active and move about rapidly when disturbed. The average life of adults is about one year. Females lay an average of about 450 eggs, which are small and clear white. The eggs are laid loosely on fine materials and broken kernels where the adults reside. The eggs are covered with a sticky secretion which the fine material adheres to. Fresh material placed in a grain bin will become rapidly infested if previous grain residue is not removed. Larvae (small brownish-white worms) hatch in five to twelve days and are full-grown in one to four months. Full grown larva are about three-sixteenths inch long and tinged with yellow. These larvae feed on fine materials and broken grain kernels. The larvae transform into small naked pupae, which are white at first and then gradually change to yellow and then to brown and shortly afterwards into the reddish-brown adult beetle. The period from egg to adult averages about six weeks under favorable weather conditions, but is greatly prolonged by cold weather, as is true of all grain pests. The life cycle of the red flour beetle is usually shorter than the confused flour beetle.

The confused flour beetle is a shiny, flattened, oval, reddish-brown beetle about one-seventh of an inch long. The head and upper parts of the thorax are densely covered with minute punctures. The wing covers are ridged lengthwise and are sparsely punctured between the ridges. The antennae of the confused flour beetle gradually enlarge toward the tip, producing a four-segment club. The red flour beetle is similar in appearance. The main distinguishing characteristics are the shape of the antennae, the head margin, and the shape of the pronotum. The red flour beetle’s antennae enlarge abruptly at the last segment giving the antennae a knobbed appearance. The head margin of this species is nearly continuous at the eyes and does not have a ridge over the eye. The pronotum is widest in the middle as compared to the confused flour beetle where the pronotum is wider toward the front margin. The wing covers are not as deeply ridged as the confused flour beetle.

Why are Confused Flour Beetles pests?

The confused and red flour beetles cannot feed on whole undamaged grain; they are, however, often found among dust, fines, and dockage. The beetles do cause damage by feeding but probably cause more problems by contaminating the grain. Large numbers of dead bodies, cast skins, and fecal pellets, as well as liquids (quinones), can produce extremely pungent odors in grain. The nauseous smell and taste caused by infestations of confused and red flour beetles can result in poor feed consumption by livestock and rejection by grain buyers. In most cases, the presence of live insects in a grain bin indicates that moisture buildup and molds are also present. The combination of these three factors can greatly reduce the quality and value of grain.