The drugstore beetle, scientifically known as Stegobium paniceum (Linnaeus), is a common pest that infests a wide range of stored products, seeds, and other materials. This article delves into the diet and life cycle of this pervasive insect, offering insights into its identification, habits, and effective control measures.
Identification of the Drugstore Beetle
Cylindrical in shape, the drugstore beetle is sometimes confused with the closely related and similar-looking cigarette beetle, Lasioderma serricorne (Fabricius). While both types of beetles appear solid brown or reddish-brown in color, certain distinguishing characteristics help separate the two species. The drugstore beetle possesses a pair of three-segmented club antennae and deep pits on the wing covers, which give the insect a striated appearance. Drugstore beetles also possess fine hairs running lengthwise along the wing covers. In contrast, the cigarette beetle is less elongate in proportion to width and has no striation on its wing covers.
Adult drugstore beetles are very active and can be identified by their rapid skittering movement. The beetles are about one-tenth inch long, light brown to reddish brown, cylindrical, and have humpbacks. Their bodies are covered with fine, silky pubescence, and they have distinct grooves in their wing covers.
Here's a summary of what to look for:
- Adults: Up to 3.2 mm (0.125 inches) long, brown to reddish brown. Similar in appearance to Cigarette beetles but has several rows of pits (striated) on hairy elytra (hardened wings). The last three antennal segments are slightly enlarged and elongated.
- Eggs: Not readily visible without magnification. Eggs are slightly oval in shape, whitish in color, satin to glossy sheen, and approximately 0.2-0.5 mm (0.019 inches) long.
- Larvae: Creamy white, C- shaped, slightly hairy, with a large distinct head, and three pairs of thoracic legs.
- Pupae: Pupal cases whitish; inside a pupal chamber within food material.
Habitat and Distribution
Although they prefer to live in warmer environments outdoors, drugstore beetles can survive just about anywhere heated shelter is available. Various commercial sites provide ideal conditions for the pests, including cereal and pet food manufacturing facilities, storage warehouses, and flour mills. On-farm grain storage, particularly of corn, is also increasingly common and provides ample food sources for these pests.
Read also: Spider Beetle Identification
Diet of the Drugstore Beetle
Drugstore beetles eat a variety of different foods. These beetles are very general feeders that attack a great variety of stored foods, seeds, and other materials, and they reportedly "eat anything except cast iron." Their food includes practically all dry plant and animal products. They may be found in stored grains where they feed on debris or dead insects and damage grain. While they cause the most damage to stored grains, seeds, and flour, the insects maintain a diverse and relatively indiscriminate diet that also includes pet foods, spices, books and manuscripts, leather, wool, hair, and even drugs, hence their common name. Museum owners should be particularly aware of this, as drugstore beetles can chew through books, paper, animal horns and antlers. In the home, these beetles damage stored and post-harvest grains and seeds, as well as packaged food products.
Life Cycle of the Drugstore Beetle
Female drugstore beetles lay as many as 100 eggs or more at a time. The eggs are pearl white and difficult to see. They are deposited in a suitable food source and typically hatch after about 10 days. Female drugstore beetle lays eggs singly in almost any dry organic substance. The eggs are oval and white and hatch in six to ten days after deposited.
The newly hatched larvae are cream-colored grubs shaped like the letter “C” and measure around 5 mm in length. Small white grubs emerge from the eggs and then tunnel through these substances. The larvae have six to nine instars and are about two-tenths inch long when fully developed. Larvae will tunnel through the food substance for about 4-5 months. The larvae form a small cocoon of silk and food material in which they pupate.
After pupating for 12 to 18 days, immature drugstore beetles emerge as adults. The entire life cycle from egg to adult takes about two months at room temperature. The life cycle on average is seven months but can be as short as two months. When the adults emerge, they disperse to find new sites to infest. This dispersal phase is what you found on your window sill.
In summary:
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- The female drugstore beetle will lay eggs in almost any dry organic substance.
- Larvae will tunnel through the food substance for about 4-5 months.
- The life cycle on average is seven months but can be as short as two months.
Impact and Damage
Substantial numbers of grain-infesting insects can reduce the value of grain or render it unfit for processing or feeding. Results of feeding by insects can reduce grain weight and quality.
The excrement these beetles leave behind can irritate the mouth, throat, and stomach if ingested. For museum owners, a drugstore beetle infestation can be equally serious, as drugstore beetles can chew through books, paper, animal horns and antlers. In the home, these beetles damage stored and post-harvest grains and seeds, as well as packaged food products. Their main impact, however, is on grain value. Their presence in grain can result in rejection of the grain by grain buyers.
Prevention and Control
Prevention is the best strategy to avoid insect problems in stored grains. Proper bin sanitation before the introduction of new grain minimizes the need for pesticides. Good sanitation involves the removal of old grain and dust in and around the grain 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. Prevention is key to protecting facilities from costly infestations.
Here are some practical steps for prevention and control:
- Do not store exposed foods on shelves or in pantries
- Store foods in glass containers with tight-fitting lids. Remember, however, that drugstore beetles will chew through plastic ware to get out.
- Clean and vacuum shelves, bins, and storage areas. Vacuum all drawers, cupboards, cracks and crevices to remove insects and food debris.
- Rotate food stock and do not mix old and new products.
- Keep food storage areas dry and clean.
- Check all organic materials in the room where the beetles were found and discard the infested products. If the infested product is something you wish to save, place it in a plastic bag and put it in the freezer for 72 hours. If it is a large object, it will have to be fumigated.
- 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.
When food items show signs of infestation, heating small quantities at a time in an oven may successfully eliminate the insects. However, this method of drugstore beetle removal proves less than sanitary and may still render the infested food inedible.
Read also: The Diets of Beetles
When proper management is ignored, populations of insects that have been feeding and reproducing in grain residues are free to infest new grain. Once in the new grain, the insects continue to eat and reproduce.
If the infested product is something you wish to save, place it in a plastic bag and put it in the freezer for 72 hours. If it is a large object, it will have to be fumigated. The room where the infestation occurred should be thoroughly cleaned. Place uncontaminated food items in glass or metal containers, or other insect-tight containers.
Fumigation should only be used as a last resort. The selective use of appropriately labeled insecticides can be used to manage and control drugstore beetle infestations.
Additional Control Measures
- Store foods in glass containers with tight-fitting lids
- Clean and vacuum shelves, bins, and storage areas
- Rotate food stock and do not mix old and new products
- Keep food storage areas dry and clean
- Place uncontaminated food items in glass or metal containers, or other insect-tight containers.
- Vacuum all drawers, cupboards, cracks and crevices to remove insects and food debris.
- Clean bins 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.
- Dispose of infested items by placing them in heavy plastic bags in the garbage, or bury deep in the soil.
What to do if you find Drugstore Beetles:
- Check all organic materials in the room where the beetles were found and discard the infested products.
- If the infested product is something you wish to save, place it in a plastic bag and put it in the freezer for 72 hours. If it is a large object, it will have to be fumigated.
- The room where the infestation occurred should be thoroughly cleaned.
- Vacuum all drawers, cupboards, cracks and crevices to remove insects and food debris.
- Place uncontaminated food items in glass or metal containers, or other insect-tight containers.
- Remember, however, that drugstore beetles will chew through plastic ware to get out.
Other control measures:
- Heating small quantities at a time in an oven may successfully eliminate the insects.
- Treatments are not effective on insects within the food packages.
- Use of a residual insecticide labeled for use in food storage/handling areas.
- Wash countertops, cabinets, and other food-related items with soap and hot water.
- Spray insecticides into cracks and crevices, or apply with a paintbrush.
- Allow surfaces to dry completely, and cover with clean paper or foil before replacing food and cooking utensils.