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Extension Entomology

Grain Beetles

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Article author: John Jackman, Bradleigh S. Vinson
Most recently reviewed by: Pat Porter (2018)

Common Name(s): Merchant Grain Beetle, Sawtoothed Grain Beetle

Description

Two of the most common grain beetles are the sawtoothed grain beetle Oryzaephilus surinamensis and the merchant grain beetle Oryzaephilus mercator. Virtually identical, sawtoothed and merchant grain beetles are around 1/10 inch long with flattened bodies well-adapted to crawling into tiny crevices. The name, Sawtoothed, is derived from the saw-like projections of the pronotum. The larvae of both species are less than 1/8 inch long and feed on broken grain and products made from processed grain.

The sawtoothed grain beetle does not fly and is not attracted to light, whereas the merchant grain beetle does fly and prefers light.

Origin and Distribution

The sawtoothed grain beetle is the most commonly encountered pest in grain and grain products, and will feed on any foodstuffs of vegetable origin. Broken grain kernels and “fines” are the principal food source, and intact kernels are not suitable as egg laying sites. The merchant grain beetle is also commonly found in grain but prefers oilseeds, including nuts.

Habitat & Hosts

These beetles are often present in high numbers in grain storage facilities. They also like to attack cereals, cake mixes, macaroni, pet food, cookies, and chocolate.  They are small enough to easily penetrate tiny cracks and crevices in packaged food products.

 

Life Cycle

The life cycle (egg, larva, pupa and adult stages) is short, producing six to seven generations a year. Adults live an average of six to ten months, but some can live three years.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Thorough inspection is needed to discover the source of grain beetle infestations. Problem areas should be inspected frequently to discover stored product pests before infestations flourish. Spilled food and grain products such as flour and cereal behind and under shelving can be a source of infestation. Sanitation and proper storage of grain products help prevent and control grain beetles. Temperatures below 0 F for 24 hours will kill all stages of grain beetles. Although detection and elimination of infested product is the key to controlling these and other stored product pests, crack-and crevice applications of appropriately labeled insecticides are sometimes warranted.

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Sawtoothed grain beetle

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Most recently reviewed by: Janet Hurley & Pat Porter (2018)

Common Name(s): Sawtoothed Grain Beetle

Pest Location

Urban Structural

Description

The adult beetle is a small (1/10 inch long), very flattened and brown with the segment just behind the head (pronotum) having characteristic “sawtoothed” outer margins, bearing six “teeth” on each side.

A closely related species, the merchant grain beetle, Oryzaephilus mercator (Fauvel), is very similar to the sawtoothed grain beetle but differs in the dimensions of the head capsule (i.e., the temple region just behind the eyes is shorter, less than the vertical diameter of the eye for the merchant grain beetle, being longer for the sawtoothed grain beetle).

Mouthparts are for chewing. Adults find their way into stored grains, flour, sugar, nuts and other dry material of plant origin through cracks and crevices of imperfectly sealed containers. They are incapable of attacking sound grain kernels and often occur in food previously infested by other stored product pests. This pest may be found infesting dry goods, crawling around kitchen surfaces and occasionally underneath tree bark.

Beetles can infest stored dry goods in the pantry; adults leave infested food sources can occur in the kitchen or other food storage areas and be a nuisance; medically harmless.

Origin and Distribution

This is a common, worldwide pest of grain and grain products as well as fruit, chocolate, drugs, and tobacco.

Habitat & Hosts

The beetle is one of the most commonly encountered stored product pests and is widespread within the food industry and can be found in food manufacturing, storage, and retail facilities, as well as in home pantries.  Prefers damaged or processed grain to establish in significant numbers. Adults can live for seveal months, females laying 300 to 400 eggs losely throughout the grain.  White larvae feed and develop externally.

Life Cycle

Fertilized females lay numerous shiny white eggs, singly or in clusters, in foodstuff and packaging. Larvae hatch from eggs in 3 to 17 days depending on temperature. Yellowish-white, deeply segmented larvae develop through several (two to four) stages (instars) while growing to about 1/8 inch long. Pupation often occurs in cells made of food particles cemented together, usually onto a solid object. Development from egg to egg occurs in 27 to 375 days. Four to six generations can occur annually.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Prevention is the best strategy to avoid insect problems in stored grains. Proper bin sanitation before introduction of new grain minimizes the need for pesticides. Good sanitation involves the removal of old grain and dust in and around the gain bin. This includes removal of old grain from corners, floors, and walls. Any grain remaining when a bin is emptied can harbor insect infestations which will move into the new grain. Grain that is to be stored for longer than six months may need a protective application of an approved insecticide.

Grain placed in a clean bin should be checked at two week intervals during warm months and at one month intervals during cooler months for the presence of hotspots, moldy areas, and live insects. If any of these conditions exist, the grain should be aerated to lower the moisture level and temperature.  Sieving and probe traps are recommended for detection.

Fumigation should only be used as a last resort. Because of the high toxicity of registered fumigants and technical knowledge needed for their proper use, a qualified pesticide applicator should be contacted if fumigation is required.

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