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Grain Beetles

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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Flour Beetles

Article author: Mike Merchant, Bradleigh S. Vinson, Wizzie Brown
Most recently reviewed by: Pat Porter (2018)

Common Name(s): Confused flour beetle, Red flour beetle

Description

Two of the most commonly found flour beetles are the confused flour beetle, Tribolium confusum, and the red flour beetle Tribolium castaneum. Virtually identical, the confused and red flour beetles are around 3/16 inch long with flattened bodies well-adapted to crawling into tiny crevices. The best way to distinguish between these two species is to look at the antenna. For practical purposes though, it does not matter which species it is because the control practices are the same.

Photo credit: Patrick Porter.

Photo credit: Patrick Porter.

The larvae of both the confused and red flour beetle are less than 1/8 inch long and feed on flour and food products made from ground and processed grain. Larvae do not penetrate whole kernels of grain, but they can feed on broken kernels and flour, corn meal etc.

These long-lived beetles are serious pests of grain processing facilities and food warehouses, but can also be found in grocery stores and home cupboards.

Red flour beetles are 1/8 to 3/16 inch long, flattened, and dark cherry to dark brown in color with gradually-clubbed antennae,  with a 3 segmented club.  They are known to fly.

Confused flour beetles are 1/8 inch long shiny, flattened, oval, reddish-brown beetle. The head and upper parts of the thorax are densely covered with minute punctures.  The antennae of the confused flour beetle gradually enlarge toward the tip, producing a four-segment club.  They cannot fly but are excellent crawlers.

Origin and Distribution

Mouthparts are for chewing. They are found in stored food products like flour, cereals and other products (e.g., dried beans, peas, peppers and fruits, shelled nuts, spices chocolate, snuff, museum specimens and some drugs). Adults and larvae feed throughout stored food, primarily in milled or prepared products. They are perhaps the most common pest of processed flour. These species are often used as a test animal in laboratory experiments because they are easy to keep in culture.

These insects are found world-wide infesting stored food; infestation may affect the flavor of product. They are medically harmless, even if eaten.

Habitat & Hosts

The confused and red flour beetles cannot feed on whole undamaged grain; they are scavengers, they feed on grain materials damaged by other pests or during transportation or storage.

Both types of beetles are often found not only in infested grains, but in crevices in pantries and cabinet, as well. Damage to food is caused somewhat by the beetles feeding, but also by their dead bodies, fecal pellets, and foul-smelling secretions. In addition to creating a foul odor, the beetles presence encourages the growth of mold.

Life Cycle

Adult beetles are active and move about irregularly. They can live for over a year. Eggs laid by females hatch in 5 to 12 days. Larvae are white, tinged with yellow, slender and cylindrical. They develop through 5 to 12 stages (instars) and grow to about 3/16 inch long over as few as 30 days. They have two short appendages on the end of the last abdominal segment. There may be 5 generations per year.

Females may lay up to 1,000 eggs during their life span, which may last several years under ideal conditions. Because adult red flour beetles are very active, can fly, and are sometimes attracted to light, they disperse easily from their initial infestation point. Adult beetles consume food.

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.

Flour beetles feed on almost every grain-based food consumed by people and their pets, so one may encounter these beetles more than any other stored food pest. Thorough inspection is required to discover the source of flour beetle infestations. Sanitation and proper storage of food is necessary to control flour beetles. Items should be inspected for infestation before being stored in the facility. Temperatures above 120 F for several hours will kill flour beetles.

Nonchemical control

The first step in controlling pantry pests is to find and eliminate infested items. Often all that is needed to solve the problem is to remove an infested package of flour, macaroni, or cake mix. But finding the source of an infestation is not always easy. Infested packages are usually the oldest, most difficult to reach foods in the pantry. Even unopened containers may be infested; some pests can easily penetrate plastic, waxed paper, and cardboard containers. Before buying an item in the store, check that the bag or container is well sealed and undamaged.

Good sanitation is important. Infestations often start in pet foods, spilled grains, or other foods. Clean up spilled food promptly. Discard old packages of grain and pasta. Vacuum and clean pantry areas periodically to remove spilled foods. Remove and clean underneath shelf paper. Caulk around pantry edges and in cracks and crevices to reduce areas where spilled food may collect.

Most pantry pest problems can be prevented by using all dried food within 2 to 4 months of purchase. Spices and other products kept for longer periods should be sealed in airtight containers.

Pet food can be a special problem.  The most commonly infested pantry items are birdseed and dog and cat foods. Store pet foods in well-sealed plastic buckets or storage containers and use them promptly. Clean the containers thoroughly before refilling them with food.

Occasionally, mice or other rodents can cause a persistent beetle infestation. Hoarded seed and grain in abandoned rodent nests can support a small population of pests. Old rodent bait that contains grain also can harbor insects. When controlling rodents, prevent insect problems by placing the bait where it can be retrieved and discarded after the rodents are controlled.

Heat or cold treatments can eliminate pests in some food items such as pet food, bulk grains and beans, and home-grown dried beans or peas. Put the product in the oven at 130 degrees F for 1 hour, or in the freezer for 7 to 14 days. To prevent an infestation, store foods that may attract pantry pests in the refrigerator or freezer.

Chemical control

On rare occasions, insecticides may be needed to control difficult infestations. Insecticides can reach inaccessible areas that cannot be easily cleaned; they can also help reduce heavy pest infestations more quickly.

Insecticide sprays may be applied to crevices and void areas around cupboards, drawers, and pantries. Before spraying, remove all food products, utensils, and containers from the treatment area. Allow the spray to dry before placing clean shelf paper on the shelves and returning food, utensils, or containers to the pantry.

Insecticide products that are labeled for use in food- storage areas generally contain ingredients that are short-lived and relatively safe to use in the home. Active ingredients of these products include pyrethrins, resmethrin, allethrin, and tetramethrin.

For areas where long-term residual control is de- sired, look for products containing synthetic pyrethroids, such as permethrin, esfenvalerate, cyfluthrin, or bifenthrin. Aerosol fog products can temporarily suppress infestations of flying insects, but these fogs will not kill pantry pests in food containers or protected locations.

Before using an insecticide, always make sure that the label says that the product may be used indoors and in kitchens. Never spray food, dishes, utensils, or cooking items with pesticides.

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Warehouse Beetle (and Khapra Beetle)

Article author: Mike Merchant
Most recently reviewed by: Pat Porter (2018)

Common Name(s): Khapra beetle, Warehouse Beetle

Description

The warehouse beetle, Trogoderma variabile, is one of several species of beetle in the genus Trogoderma that are considered pests of stored products. It is the most common Trogoderma pest in homes. The warehouse beetle is oblong to oval, 1/8 to 3/16 inch long, with a dark and light mottled pattern on their wing covers. Adult Trogoderma are fairly short-lived and rarely feed on stored products. However, they are considered excellent fliers and can disperse quite easily.

Warehouse beetle immatures are cigar-shaped and hairy.  Trogoderma larvae have hastisetae, which appear as darker or longer clumps of hairs, and arise directly from the tops of the plates on the last three abdominal segments. These hastisetae can cause gastrointestinal problems if ingested by humans.

It should be noted that the warehouse beetle is a close relative of a highly destructive and tightly quarantined pest called the Khapra beetle Trogoderma granarium. Khapra beetle also known as cabinet beetle is considered one of the 100 worst invasive species in the world.  Because of their warm climates, the Khapra beetle has the most potential for establishment in Arizona, California, Kansas, New Mexico, Oklahoma and Texas. The Khapra beetle is a destructive pest of stored grain and other dried plant—as well as animal—products. It is able to survive almost anywhere in storage facilities that are protected from cold environments. This pest is known for its “dirty eating” behavior; by feeding only a little on each grain, one tiny beetle can damage a surprising amount of stored product.  If you suspect you have a Khapra beetle you MUST contact the United States Department of Agriculture, Animal and Plant Health Inspection Service in your area.

Origin and Distribution

This beetle feeds on a wide variety of foods including cereals, candy, cocoa, cookies, corn, corn meal, fish meal, pets foods, flour, nets, dried peas and beans, potato chips, pastas, spices, dead animals and dead insects.  The warehouse beetle occurs throughout the United States and is common in seaports throughout the world.

Habitat & Hosts

When food becomes scarce or disappears, Trogoderma larvae may enter a lengthy period of inactivity known as diapause, where insects are completely inactive and do not feed. When larvae break diapause, they can resume infesting food items. This ability to diapause in the absence of food combined with the ability to chew through packaging can make control of Trogoderma beetles difficult.

Life Cycle

Females lay around 90 eggs in a lifetime, and the resulting offspring go through a life cycle that takes anywhere from two to four months to complete. In cases of food shortages or poor environmental conditions, warehouse beetle larvae can slow their development by molting numerous times before deciding to pupate.

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.

Warehouse beetles are among the most difficult indoor pests to control because of their ability to find food in obscure places and to disperse widely throughout a building. Successful control depends on a combination of sanitation and exclusion. If exclusion and sanitation are successful, insecticide treatments aren’t required.

When warehouse beetles threaten products in commercial warehouses or storage areas, a monitoring program using sticky traps baited with an appropriate pheromone  is recommended. Sticky traps can also be used in homes where infestations are serious. Traps placed throughout a building can show where beetles are coming from; the traps are also useful for monitoring the effectiveness of control practices. Check traps once or twice a week. You can also use pheromone traps to augment other control methods if you use them to attract adult males in small confined areas. Sticky traps are also available without a pheromone; you can place these traps on windowsills to trap adults that fly to windows.

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Cigarette and Drugstore Beetle

Article author: Mike Merchant
Most recently reviewed by: Pat Porter (2018)

Common Name(s): Cigarette Beetle, Drugstore Beetle

Description

Cigarette and drugstore beetles are often confused with one another. Adult beetles are rounded in profile, oval shaped, light-brown color, 1/16-1/8 inch-long. A hood-like shield (prothorax) encloses and conceals the head when viewed from above. The femora of each hind leg retracts into a groove in hind coxa. These beetles can be distinguished by the grooving on the wing covers and by their antennal shape. The drugstore beetle’s wing covers possess distinct striae, or grooves, and its antennae are clubbed with three elongated and broadened segments at the tips. The wing covers of cigarette beetles are very smooth, without distinct grooves; and the antennal segments are sawlike, or serrate.

Drugstore beetles are 1/16 to 1/8 inch long. they are brown, and their elytra have distinct rows of pits.  Their antennae end with a loose, three-segmented club. Compared to the cigarette beetle the body is thinner and pronotum is more pronounced.

Cigarette beetles are 1/16 to 1/8 inch long and brown, the elytra is smooth with no grooves. When viewed from the side the angle at which the pronotum borders the elytra gives this beetle a humpbacked appearance. The antennal segments are serrate.

Origin and Distribution

These two species are among the most common stored product pests in Texas homes. They feed on all kinds of plant material including tobacco, seeds, grain, nuts, beans, spices, cottonseed meal, dried fruits and vegetables, flour, spices, and dried herbarium specimens. Animal products such as dead insects, dried fish and fish meal, and leather may also be attacked. On grains, these insects are classified as external feeders. Adults and larvae feed primarily on the outside of the grain, though they may also chew through the outer coat and devour the insides. Both species are among the most common stored product pests both in homes and in commercial food processing and distribution facilities, worldwide. Neither of these beetles bite.

Habitat & Hosts

Both of these beetles are attracted to light and are external feeders.  However, their larvae will stay close to a food source and they do not fly until they reach adult stage.

Life Cycle

Females lay up to 100 eggs over a 6-20 day period in crevices, folds, or depressions in their food. The time needed to develop depends on the food source and other environmental conditions, but ranges from 26 to over 100 days (commonly, 30-50 days). Optimal conditions for development are 70-80% RH, and temperatures between 68° and 86°F. Development generally ceases below 59°F and above 94°F.

The number of larval instars ranges from four to six. Newly hatched larvae are very active and can enter food packaging through very small holes, including minute seams around lids of spice containers. Pupation occurs in loosely constructed pupal cells within the food source. Adults of both species can fly.

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.

The keys to managing an infestation of cigarette or drugstore beetles include good sanitation, early detection and locating and destroying infested materials.  Insecticides alone are rarely effective. Check all stored food packages and potential food items listed above, and discard any infested food products that you find. Other places to look:

  • Pet foods are common sources of infestation. In addition to checking product bags, look in difficult to clean areas, where pet food or bird seed may have spilled.
  • Old school art projects involving beans, nuts or seeds
  • Forgotten bags of pecans, other nuts
  • Spices, potpourri, other dried plant material
  • Cigarettes, pipe tobacco
  • If your home has been previously infested with a mouse or rat, old rodent nests can be infested. Rodents often hoard food, such as seed or dog food, in their nests. After the rodents leave or are controlled, the food in abandoned nests can be the source of a difficult-to-locate infestation.
  • Rodent bait.  Bait packets thrown in corners of attic or crawl space can be a source years after placement.

Heat treatment is routinely employed against these and other insect pests in museums when receiving new artifacts, like herbarium specimens. Heating artifacts to 125°F for two to four hours, or freezing infested materials at 0°F for six days, is generally sufficient to kill all life stages of anobiid beetles. Small quantities of pet food may be dis-infested by placing in a cold freezer for two weeks. Pet food treated in this manner can then be safely fed to pets.

Dried flower arrangements can be protected to some extent by treating storage containers with a desiccant dust like silica aerogel or diatomaceous earth. Dust the box or container lightly before placing the flowers inside.

Pheromone traps have been developed for both species. These traps use a special sex-scent to attract male beetles. Effectiveness of these traps can be enhanced by placing them near windows or other light sources. In commercial operations pheromone traps can be used to determine where infestations are located and when aerosol applications of pesticides may be needed. Aerosol applications of insecticides like pyrethrins or resmethrin can suppress adult cigarette beetle populations temporarily, but do not eliminate larval infestations.

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