Home stored product entomology is the study of insects which infest foodstuffs stored in the home. It deals with the prevention, detection and eradication of the pests. The five major culprits considered in this article are flour beetles, the drugstore beetle, the sawtoothed grain beetle, the Indianmeal moth and fruit flies.
This is an important branch of forensic entomology because consumers who find products that are contaminated may choose to take legal action against the producers. A suitably qualified entomologist is likely to be able to determine the identity of contaminant species even when no insects are found and the only evidence of infestation is the resulting damage. He or she should also be able to determine whether the foodstuff was contaminated before or after purchase. Companies are required by the U.S. Food and Drug Administration (FDA) to have no more than a certain number of larvae, insects or insect fragments in their product, and it is when this defect action level is exceeded that a consumer can prosecute.
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There are two different types of beetles classified as flour beetles: the red flour beetle and the confused flour beetle. Both are similar in physical characteristics. They are flat and oval in shape and usually range around 1/8- inch long. Their exoskeleton is reddish brown with a shiny and smooth texture. The eggs, larvae, and pupa resemble each other closely in physical features as well. The eggs usually tend to be a white color, or at times even colorless. They are very small in size and have a sticky outer covering that causes certain food particles to stick to it. The larvae have six legs, with two pointy projections toward the caudal end. Finally, the pupal stage (a cocoon-like form used to break itself down and emerge as a mature adult) is usually a white or brownish color. The beetle life cycle lasts approximately 3 years or more, with the larval stage ranging anywhere from 20 to over 100 days, and the pupal stage around 8 days. Beetles usually breed in damaged grain, grain dust, high-moisture wheat kernels and flour. The female flour beetle can lay between 300 and 400 eggs during her lifetime [a period of 5 to 8 months]. The flour beetles mainly infest grains, including, but not limited to: cereal, corn meal oats, rice, flour, and crackers. This type of beetle is the most abundant insect pest of flour mills across the United States. Their small size allows them to maneuver through cracks and crevices and get into the home and other areas. Once they are present in areas with potential food sources, they can infest material such as flour, resulting in a sharp odor or moldy flavor. The red flour beetle is able to fly short distances and the confused flour beetle is unable to fly. While the confused flour beetle is more commonly found in the northern United States, the red flour beetles are more predominant in the southern United States in areas with warmer climates.[1]
The red flour beetle is considered the best organism to study genetics. A team composed of Susan Brown and Rob Denell, both biology professors at the University of Kansas, along with Richard Beeman, won financial support to have the beetle's genome sequenced, marking it as one of the earliest sequenced insect genomes, as well as distinguishing the red flour beetle as the only pest insect to be analyzed in this way thus far. The project was funded partially by the US Department of Agriculture, as well as by the National Institutes of Health, and the genome sequencing was led by Stephen Richards at the Human Genome Sequencing Center, Baylor College of Medicine. The red flour beetle's gene map information and genomic sequence are accessible from the National Center for Biotechnical Information. More information is to be published in Nature on 2008-03-27.[2]
This beetle is closely related to the commonly known cigarette beetle. Adult drugstore beetles are cylindrical with lengths ranging from 2.25 to 3.5 mm. These beetles are a reddish brown color and have elytra, sclerotized (hardened) wings that fold back over the abdomen and hinge upwards, allowing the hind wings to come out in order to fly. Females are capable of laying up to 75 eggs during a 13 to 65 days. After the eggs are laid they move into a larval period that can range anywhere from 4 to 20 weeks. After the larval period, drugstore beetle larvae move out of the substrate to build a cocoon and pupate. The pupation period takes a total of 12–18 days. The entire life cycle of the drugstore beetle lasts approximately 2 months but can be as long as 7 months. These stored product pests will infest almost anything readily available. Food products prone to infestation include: flours, dry mixes, breads, cookies and other spices. Non-food material includes: wool, hair, leather and museum specimens. This specific type of beetle has symbiotic yeasts that produce B vitamins, which allow the beetle to survive even when consuming foods of low nutritional value. They are found in areas that have a warmer climate, yet are less plentiful in the tropics than their counterpart, the cigarette beetle.[3]
The sawtoothed grain beetle is closely related to the merchant grain beetle, and is commonly found in kitchen cabinets feeding on items such as cereal, breakfast foods, dried fruits, macaroni, crackers, etc. They are the most common grain and stored product pest in the United States. They are very active and tend to crawl rapidly while searching for food.[4] They are small insects, reaching a length of about 1/8 of an inch. Their name originates from their distinguishable saw-tooth-like projections found on each side of the thorax. The body shape of the beetle is flat, slender, and brown in color. The size and shape of the mandibles allow the beetles to easily break through well sealed and packaged foods. An adult female sawtoothed grain beetle can lay anywhere between 45 to 250 eggs that usually hatch within 3 to 17 days. The larvae look much different from the mature adult. They have a caterpillar-like appearance, with a yellowish coloration to the body and a brown head. The larval period can last as long as 10 weeks but can be as short as 2 weeks. Following the larval instars is the pupal period, which can last one to three weeks. The pupal stage is characterized by the unique process by which these beetles stick together pieces of food material to form a protective covering around their bodies. A fully mature adult beetle, under optimal conditions, can live a maximum of 4 years, a long lifespan for an arthropod.[5]
Indianmeal moths can infest a variety of foods found in the home. Coarsely ground grains, cereals, dried fruits, and herbs are common items the moths have been known to infest. They have also been found in animal food such as dry dog food, fish food and even bird seed. The adult moth is small; generally, their length averages about 3/8 inch, with a 5/8 inch wing span. As adults, the moths are easily identified by an overall grayish, dirty complexion. However, the wing tips have a bronze color that helps differentiate this particular moth from other household moths. The adults have a distinct forewing pattern as well which consists of a light-colored base with about two-thirds of the distal area a red to copper color.[6] The larval stage, or caterpillar, is characterized by a pinkish or yellowish-green body color with a dark brown head. The larval stage of the moth’s life cycle is centered on food sources; during the last instar, these larvae are characterized by a movement towards a protected area to pupate. These caterpillars have the capacity to chew through plastic packaging and will often produce silk that loosely binds to food fragments. The pupal stage is generally observed as tiny cocoons that hang from the ceiling; these cocoons can also be found on walls, as well as near the food source. A female can lay over 200 eggs, and will usually die after this process because adults Indian meal moths do not eat.[7]
Fruit flies are found near ripened or fermenting fruit. Tomatoes, melons, squash, grapes and other perishable items brought in from the garden are a common cause of an indoor infestation. Fruit flies can also be attracted to rotting bananas, potatoes, onions and other unrefrigerated produce purchased at the grocery store and taken home. The body of the fruit fly is tan towards the front part of the body and black towards the rear. They usually have red eyes and are about 1/8 inch long. Females have the ability to lay over 500 eggs, usually in fermenting fruit as a food source. The only environment necessary for successful reproduction is a moist film and fermenting material. Generally, fruit flies are a problem during late summer and fall due to their attraction to ripening and fermenting fruits and vegetables. The entire life cycle can be completed in about a week. Unfortunately, because of their ability to fly in and out of the home through windows and screens, they have the capability of contaminating food with bacteria and disease-producing organisms.[9]
Careful observation is necessary when detecting the culprit of an insect infestation. Each of the five different insects discussed has a unique pattern of destruction. These observations are imperative, as there are not always larvae, pupa, or adults readily available for examination and identification. In the absence of physical specimens, conclusions can be drawn about the probable insect that is infesting the product just by noting the damage done to the particular food. By noting the type of food and the damage done, a nearly accurate conclusion can be drawn about the type of insect causing the damage, allowing a conjecture about the type of control needed. Having an insect specimen and accurately identifying it can lead to eradication, and ultimately, prevention.
Foods commonly infested include:
Other items include, but aren’t limited to: Rodent baits (that contain grain as a feeding attractant), dry pet food, bird seed, grass seed, some powdered soap detergents, dried flowers, potpourri, items stuffed with dried beans or other plant material, and tobacco products.
In order to identify an insect, and consequently make a decision about the type of control to be implemented, the type of food must first be noted, especially in the absence of a specimen. Although identifying the food is a general start to begin to identify the insect, it must be remembered that it isn’t always the most accurate method. It is mostly used as a guideline, as some insects are more likely than others to be found in certain types of grain, flour, etc. The type of food is not always conclusive to the type of insect found in it, as insects are not extremely picky, and many families and species are found on a wide range of different foodstuffs. Using the infested item as a guideline, noting the type of damage done to the product is the next step. Some insects, like the drugstore beetle, leave telltale tiny holes in the damaged product, while Indianmeal moths are notorious for the spider web-like threads left behind in the food they infest. These observations can generally lead to a mostly accurate conclusion about the type of insects that are causing the damage, but obviously the most accurate conclusion relies on any specimen found either directly in the stored product or in the vicinity. The larvae, pupae, and adults can be found directly in the product while usually only the pupae and adults are found in the vicinity of the product. It is not practical to assume that any person has knowledge of general entomology, so the following analysis focuses on the five major pests that most commonly infest stored products, beginning with the type of foods infested, signs indicative of a particular insect infestation, and a description of the larvae, pupae, and adults, including behavior as well as appearance.
This beetle is similar to the sawtoothed grain beetles in both habits and types of products infested. It is a serious pest in flour mills and wherever cereal products and other dried products are stored and/or processed. Generally, the beetle is attracted to grain with a high moisture content, and usually causes the grain to acquire a grayish tint. The beetle may also impart a bad odor, which then affects the taste of the infested products, as well as encouraging the growth of mold in the grain. This foul odor and taste in the various food products are caused by pheromones and toxic quinone compounds.[10]
The sawtoothed grain beetle feeds on a plethora of feeds, but is not capable of attacking whole or undamaged grains; therefore, it is commonly found in processed grains (flour and meal), dry dog food, dried fruits, candy bars, tobacco, drugs, dried meats, and a variety of other products. It is one of the most common insects found to infest stored products. Larvae are found to develop in flour, dried foods, cereal products, and other stored products.[11][12]
These beetles will infest almost anything- they are found most often, however, in flour, bread, spices, breakfast foods, and meal. In the case of an infestation, contaminated products have telltale tunnels which have the appearance of tiny holes. These beetles do not sting, bite, or harm pets or damage a house, yet have the potential, in large infestations, to become a nuisance by flying on doors and windows in heavy populations.
Indianmeal moths infest both cereal and stored grain products, packaged goods, grain in storage, and surface layers of shelled corn. The most telltale sign of the Indianmeal moth is the silk webbing that the larvae (caterpillars) produce when feeding on the surface of foods. This silk webbing may appear to be or resemble cobwebs inside the products container. Often, a few larvae may be found in the packaging of the product, along with the ‘cobwebs’, cast skins and frass.
Larvae are white worms with black heads, which, when ready to pupate, crawl up the walls of the home in most cases, and are suspended from the ceiling attached by a single silken thread. Most complaints about these moths come during the warmer parts of the year- usually the months of July through August- but the moths have the capability to appear during any month. As with all insects important to stored product entomology, it cannot be automatically assumed that products were previously infested, yet, it is more common for these moths to hitchhike inside a product or in groceries than for the moth to fly into a home through open windows or doors. An important aspect of the Indianmeal moth is that the larvae are the only stage of the insect’s life cycle to feed on stored products, the adults do not.
Fruit flies are attracted to ripened fruits and vegetables, usually in the kitchen area, but will breed in garbage disposals, empty bottles and cans, wet or damp mops or cleaning rags, and trash containers. The only requirement for these flies to breed is a moist film of fermenting material. Infestations can originate from over-ripened fruits or vegetables that were previously infested, and then brought into the home or from fruit over-ripening in the home. Since adults can also fly from the outside through screened doors or windows it can not always be assumed that the product in question was infested before it was brought into the home. The larvae are found on the inside layer of the fruit, just directly beneath the skin. If the outer layer of the fruit is removed, the rest of the fruit can be salvaged. Fruit flies are primarily a nuisance pest, yet they can infect food with bacteria and other organisms that cause diseases.
Defect action levels have been a part of the food industry for nearly a century. The first established defect action level was created in 1911 for mold in tomato pulp. However, limits for insect fragments and larvae were not added until the 1920s on various fruits and vegetables. In 1938, the Federal Food, Drug and Cosmetic Act was established to provide a more defined reference based on strict limitations and methods.[13]
Major companies spend a large amount of money every year to aid in the prevention of food contamination. Most of these dollars are well-spent and do, in fact, prevent food from becoming contaminated on a large scale; however, there are many "defects" in consumers' meals on a daily basis. The Food and Drug Administration states, “it is economically impractical to grow, harvest, or process raw products that are totally free of non-hazardous, naturally occurring unavoidable defects”.[14]
The general public proposes that companies should use more chemicals or pesticides to control this “problem”. Though, the amount of pesticide and chemicals necessary to eradicate all insects from foodstuff would pose a threat to any human’s health; much more harmful than a controlled quantity of insect and rodent fragments. The Food Defect Action Levels, as proposed by the FDA, is a list of ordinances and guidelines manufacturers and industrial food agencies must abide to ensure the safe service of foodstuff. However, these detection levels are labeled with maximum limitations only. Due to the impossibility of preventing all unavoidable defects in foods, the FDA attempts to prevent these health hazards from reaching a harmful level. Therefore, it is understood and regarded that all manufactures are allowed to have low numbers of insect and rodent hairs present in food, as long as the product is still considered “safe” for human consumption. Shown below are a few examples taken from the FDA's Defect Action Level Handbook:
| APPLE BUTTER | Mold (AOAC 975.51) |
Average of mold count is 12% or more |
| Rodent filth (AOAC 945.76) |
Average of 4 or more rodent hairs per 100 grams of apple butter | |
| Insects (AOAC 945.76) |
Average of 5 or more whole or equivalent insects (not counting mites, aphids, thrips, or scale insects) per 100 grams of apple butter |
DEFECT SOURCE: Mold - post harvest infection. Rodent hair - post harvest and/or processing contamination with animal hair. Whole or equivalent insects - preharvest, and/or post harvest and/or processing insect infestation,
SIGNIFICANCE: Aesthetic
| CHOCOLATE AND CHOCOLATE LIQUOR | Insect filth (AOAC 965.38) |
Average is 60 or more insect fragments per 100 grams when 6
100-gram subsamples are examined |
| Rodent filth (AOAC 965.38) |
Average is 1 or more rodent hairs per 100 grams in 6 100-gram
subsamples examined |
|
| Shell (AOAC 968.10-970.23) |
For chocolate liquor, if the shell is in excess of 2% calculated on the basis of alkali-free nibs |
DEFECT SOURCE: Insect fragments - post harvest and/or processing insect infestation, Rodent hair - post harvest and/or processing contamination with animal hair or excreta, Shell - processing contamination
SIGNIFICANCE: Aesthetic
| CITRUS FRUIT JUICES, CANNED | Mold (AOAC 970.75) |
Average mold count is 10% or more |
| Insects and insect eggs (AOAC 970.72) |
5 or more Drosophila and other fly eggs per 250 ml or 1 or more maggots per 250 ml |
DEFECT SOURCE: Mold - processing contamination, Fly eggs and/or maggots - post harvest insect infestation
SIGNIFICANCE: Aesthetic
| CORNMEAL | Insects (AOAC 981.19) |
Average of 1 or more whole insects (or equivalent) per 50 grams |
| Insect filth (AOAC 981.19) |
Average of 25 or more insect fragments per 25 grams | |
| Rodent filth (AOAC 981.19) |
Average of 1 or more rodent hairs per 25 grams OR Average of 1 or more rodent excreta fragment per 50 grams |
DEFECT SOURCE: Insects and insect fragments - preharvest and/or post harvest and/or processing insect infestation, Rodent hair and excreta fragments - post harvest and/or processing contamination with animal hair or excreta
SIGNIFICANCE: Aesthetic
| HOPS | Insects (AOAC 967.23) |
Average of more than 2,500 aphids per 10 grams |
DEFECT SOURCE: Pre-harvest infestation
SIGNIFICANCE: Aesthetic
| PEANUT BUTTER | Insect filth (AOAC 968.35) |
Average of 30 or more insect fragments per 100 grams |
| Rodent filth (AOAC 968.35) |
Average of 1 or more rodent hairs per 100 grams | |
| Grit (AOAC 968.35) |
Gritty taste and water insoluble inorganic residue is more than 25 mg per 100 grams |
DEFECT SOURCE: Insect fragments - preharvest and/or post harvest and/or processing insect infestation, Rodent hair - post harvest and/or processing contamination with animal hair or excreta, Grit - harvest contamination
SIGNIFICANCE: Aesthetic
| PEPPER, GROUND | Insect filth (AOAC 972.40) |
Average of 475 or more insect fragments per 50 grams |
| Rodent filth (AOAC 972.40) |
Average of 2 or more rodent hairs per 50 grams |
DEFECT SOURCE: Insect fragments - post harvest and/or processing insect infestation, Rodent hair - post harvest and/or processing contamination with animal hair or excreta
SIGNIFICANCE: Aesthetic
| WHEAT | Insect damage (MPM-V15) |
Average of 32 or more insect-damaged kernels per 100 grams |
| Rodent filth (MPM-V15) |
Average of 9 mg or more rodent excreta pellets and/or pellet fragments per kilogram |
DEFECT SOURCE: Insect damage - preharvest and/or post harvest and/or processing infestation, Excreta - post harvest and/or processing animal contamination.
SIGNIFICANCE: Aesthetic
| WHEAT FLOUR | Insect filth (AOAC 972.32) |
Average of 75 or more insect fragments per 50 grams |
| Rodent filth (AOAC 972.32) |
Average of 1 or more rodent hairs per 50 grams |
DEFECT SOURCE: Insect fragments - preharvest and/or post harvest and/or processing insect infestation, Rodent hair - post harvest and/or processing contamination with animal hair or excreta.
SIGNIFICANCE: Aesthetic
To prevent the infestation of foodstuffs by pests of stored products, or “pantry pests”, a thorough inspection must be conducted of the food item intended for purchase at the supermarket or the place of purchase. The expiration date of grains and flour must also be noted, as products that sit undisturbed on the shelf for an extended period of time are more likely to become infested. This does not, however, exclude even the freshest of products from being contaminated. Packaging should be inspected for tiny holes that indicate that there might be an infestation. Foodstuffs susceptible to infestation in particular include dried grains, flour, cereals, and whole-grain products. If there is evidence of an insect infestation, the product should not be purchased. The store should be notified immediately, as further infestation must be prevented. Most stores have a plan of action for insect infestations. Bringing an infested product into a pantry or a home leads to a greater degree of infestation. In the home, putting cereal or grain type items in preventative containers will also help to prevent an infestation or the spread of insects from one product to another. Insects can chew through thin plastic, foil, cardboard and other packaging that the product is put in for resale; transferring purchased products into heavy glass containers that can be tightly sealed or heavy plastic containers can improve sanitation and prevent infestation. Using the oldest products first and buying grains and cereals in smaller quantities which can be used up quickly, depending on the size or intake of the family, decreases the chances of infestation. Fruit flies, however, present an entirely different approach to prevention. The primary method to controlling and eliminating fruit flies is to eradicate sources of attraction. Ripened produce should be either eaten, discarded, or refrigerated. Any fruit or vegetable that is damaged or cracked needs to be cut, and the damaged piece discarded in the case that larvae or eggs are present in the area in question. Careful attention must be paid to potential breeding sites that, when forgotten, could cause a massive infestation- all recycling and compost bins must be cleaned, and areas must be checked for forgotten, rotting fruit. Because of their small size, fruit flies are capable of breeding on the inside of the lid of a container. Therefore, it is imperative that when personally canning fruits or vegetables, beer, cider, or wine, that the container is well-sealed. Adults moths can lay eggs under the lid of a jar, allowing the larvae to crawl into the food source when hatched. Homeowners should also outfit their doors and windows with tight mesh screens that prevent the adult fruit flies from flying in from outdoors. Preventative methods and sanitation are the keys to avoiding an infestation or contamination of foodstuffs.[15][16]
Although not seen when groceries are purchased, some products have the possibility of being infested prior to being placed in the pantry. A periodical check of susceptible foodstuffs is necessary, especially in summer months when most insects are more active. In the event that an infestation is discovered, steps must be taken to eradicate the insects. Controlling an infestation is a lengthy process and insects may still be seen, albeit in dwindling numbers, for several weeks. All infested items, as well as noninfested items, must be removed from shelves, thoroughly cleaned and vacuumed. After vacuuming, the waste containing the infested material must be removed and discarded. Items should be checked for beetles, larvae, and pupa; it must be ensured that all food items are inspected as well, and special attention must be paid to items that have been rarely used. The infested items may either be discarded, heated or frozen to kill the insects. If the food is chosen to be discarded, the item must be completely removed from surrounding premises in order to prevent reinfestation. Freezing products for three to four days or heating them to about 130 to 140 degrees Fahrenheit for 30 to 40 minutes will rid the product of the pests. Decorative ornaments and objects made with plant material and seed located in the vicinity of stored products will increase the risk of reinfestation: insects can feed on those items until they locate stored products. These items should also be thrown out or eradicated by freezing or heating. Cleaning the area where the infested products were found is advisable, as well. Cleaning with bleach or ammonia, however, will not help with the eradication of the pests. Using a vacuum cleaner to clean the area thoroughly, especially in cracks and corners where insects may hide, will decrease the chances of reinfestation. Because food will be stored in that area again, pesticides are not a good method of eradication. Pesticides can leave a residue that can contaminate food products stored near it. Also, once a pest is inside the container, the pesticides have no effect. If the infestation is so severe that pesticides are the only way to contain the problem, a professional should be contacted immediately. Do not try to apply pesticides to any area where food is stored for human or animal consumption. Contamination can occur and cause illness or more severe conditions. Proper storage and cleanliness are the only ways to prevent an infestation from occurring. Sanitation is the key to prevention and eradication of any pests.[15] [16]
If these insects are found infesting stored products, it is not practical to automatically assume the store or producer is at fault. Although some infestations are not the consumer's fault, producers are held by the FDA action defect levels to ensure their product does not contain more than the allotted amount of insects/insect fragments/larvae. If a stored product is found to be infested by insects, and it is suspected that someone other than the consumer is at fault, a forensic entomologist can be contacted to make a determination. Again, it should not be assumed that these are the only five insects found in a common household pantry, but due to the large number of infestations by these five major groups, it can be safely deduced that it is perhaps one of these five. Stored product entomology is an important forensic field that is important to not only the government and the FDA but the general public, as it is involved in the consumption of food in everyday life.
Other stored product pests:
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