Home-stored product entomology

Introduction

Stored product entomology is used most commonly in lawsuits over the contamination or infestation of foods by insects, usually in the commercial sector. Although stored product entomology may seem a lesser-known subject, this branch of forensic entomology is extremely important, as it encompasses all cases involving the finding of insects in any food products. A stored product entomologist’s job is determining if the product was truly infested before it was shipped or purchased by the consumer, and whether or not legal action can be taken against the producer. These entomologists are so important, and these cases so common, that many large food companies actually hire a forensic entomologist to keep on staff to assist in court proceedings involving a contaminated product. Companies are required by the FDA to have no more than a certain number of larva/insects/insect fragments in their product, and it is when this defect action level is exceeded that a consumer can prosecute. Because of the huge number of lawsuits that involve finding insects in food, a stored product entomologist is extremely important to the integrity of the company, as well as the safety of the consumer. Stores often have special employees whom are notified in the case of an infestation, in order to take action quickly to prevent further food contamination. Although many of these cases are justified, some are just scams of people looking to make money, and in the latter case, a stored product entomologist can effectively make a determination as to who is at fault. On the other hand, stored product entomology does not focus on just purely legal court proceedings; rather, it also deals with the prevention and eradication of common household insects, five of which are identified in the following paragraphs. The average person is not primarily concerned with lawsuits involving large companies, but rather the health and well-being of themselves and their families. Five major household pantry insects that are found most commonly in stored foodstuffs include the red flour beetle, the drugstore beetle, the sawtoothed grain beetle, Indian meal moths, and fruit flies. Stored product entomology includes a plethora of other insects, but these five are the insects that are found most often in food items in a house or a pantry. There are thousands of other species of insects that infest other areas, such as weevils, yet this is focused chiefly on the insects that are reported to be the most common.

Five Major Home-Stored Product Pests

Flour Beetles (Tribolium castaneum and Tribolium confusum)

There are two different types of beetles that are classified as flour beetles. They are 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, the outer covering, 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 consist of six legs, with two pointy projections toward the rear. Finally, the pupae 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 last approximately 3 years or more, with the larval stage ranging anywhere from 20 to over 100 days, and the pupal stage taking around 8 days. Beetles usually breed in damaged grain, grain dust, high-moisture wheat kernels, and flour. The female flour beetle can lie between 300 and 400 eggs during a lifetime [with from a period of 5 to 8 months]. The flour beetles infest mainly grains, including, cereal, corn meal oats, rice, flour, crackers, and other grain products. This type of beetle happens to be 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 these areas they can infest material such as flour, resulting in a sharp odor or moldy flavor. The Red flour beetle is able to fly short distance and the Confused flour beetle is not able 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 around warmer climate.

Drugstore Beetle (Stegobium paniceum)

File:Drugstore Beetle.JPG

Drugstore Beetle

The Biscuit beetle is closely related to the commonly known Cigarette beetle. Adult Drugstore beetles are shaped cylindrically with dimensions ranging from 2.25 to 3.5 mm. Their exoskeleton consists of a reddish brown coloring and contains elytra. Elytra are sclerotized (hardened) wings that fold back over the abdomen and hinge upwards allowing the hind wings to come out in order to have flight, as is true with all beetles. The presence of this physical feature with the striated appearance on them helps distinguish the Drugstore beetle from its similar Cigarette beetle. Females are capable of laying up to 75 eggs during a life time. 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 larvae move out of the substrate to build a cocoon and pupate. The pupation process takes a total of 12-18 days. The entire life cycle of the Drugstore beetle lasts approximately 2 months or up to as long as 7 months. Adult female beetle’s have a lifespan of about 13 to 65 days. These stored product pests will attack almost anything that they can get in to. Food products that they are likely to attack are flours, dry mixes, breads, cookies, and other spices. Non-food material they tend to feed on includes wool, hair, leather, and sometimes they will infest museum specimens. This specific type of beetle is able to produce symbiotic yeasts that produce B vitamins. The production of this vitamin allows the beetle to survive on the consumption of poor nutritional foods. They are found in areas that have a warmer climate, and are less plentiful among the tropics as their counterpart, the Cigarette beetle.

Saw-toothed Grain Beetle (Oryzaephilus surinamensis)

Saw-toothed Grain Beetle

The Saw-toothed grain beetle, closely related to the Merchant grain beetle, is commonly found in kitchen cabinets feeding on items such as cereal, breakfast foods, dried fruits, macaroni, crackers, etc. They are small insects, reaching roughly around 1/8 of an inch. Their name marks their distinguishable saw-tooth-like projections found on each side of their thorax. Their body shape is flat, slender, and is brown in color. Their size and shape allow them to easily break through well sealed and packaged foods. They also have the capacity to chew through items that are packaged in paper. An adult female Saw-toothed grain beetle can lie anywhere between 45 to 250 eggs, that are usually hatched in a range of 3 to 17 days. The larvae look much different from the mature adult. They have a yellowish coloration along with a brown head. The larval period can last as long as 10 weeks and as short as 2 weeks. Proceeding from the larval period, they will move into pupation. This occurs by sticking together pieces of food material to form a protective covering around their bodies. This can last anywhere from 1 to 3 weeks. A fully mature adult beetle, under perfect conditions can last a maximum of 4 years which is quite long for an insect to live.

Indian Meal Moths (Plodia interpunctata)

Indian Meal Moth

Indian meal moths are found in a variety of foods found in the pantry. Coarsely ground grains, cereals, dried fruits, and herbs are common items the moths infest. They have also been found in animal food such as dried dog food, dried fish food, and sometimes bird seed. The adult moth is small; generally, their size averages about 3/8 inch, with a 5/8 inch wing span. As adults, the moths are easily indentified 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 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 either hang from the ceiling; these cocoons can also be found on walls, as well as near the food source. A female can lie over 200 eggs, and will usually die after this process because as adults Indian meal moths do not eat.

Fruit Flies (Drosophila melanogaster)

Fruit Fly

Fruit flies are pests that are found around ripened or fermenting fruit. Tomatoes, melons, squash, grapes and other perishable items brought in from the garden are a common cause of infestation developing indoors. Fruit flies are also 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.

Detection of an Infestation

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:

Whole or cracked grains (rice)

Flour, meal, or similar ground grain products

Spices

Cereals

Pasta

Candy

Powdered milk

Nuts (whole or pieces)

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 Indian meal 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.

Red Flour Beetle Detection

This beetle is similar to the Saw-toothed grain beetles in both habits and types of products infested. This beetle 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. The adult Red flour beetles are about 3/16 inch long, are reddish brown, and elongate oval in shape. The larvae are shaped like cylinders, are white or cream colored, and are usually identifiable by two small pointed spines on the tail end. The larvae are generally larger than the adults- about ¼ inch long. The confused red flour beetle and the red flour beetle are very similar; the difference lies in the ability of the red flour beetle to fly short distances.

Saw-toothed Grain Beetle Detection

The Saw-toothed grain beetle feeds on a plethora of feeds, but is not capable of attacking whole or undamaged grains, therefore; is 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 that are found to infest stored products. Larvae are found to develop in flour, dried foods, cereal products, and other stored products. As adults, these beetles do not fly, nor are they attracted to light. Adult females can live for several months to more than a year.

Drugstore Beetle Detection

These beetles will infest almost anything- they are found most often, however, in flour; bread; spices, like red pepper; breakfast foods; and meal. In the case of an infestation, contaminated products have telltale tunnels which have the appearance of tiny holes. Larvae are about 1/8 inch long, are yellowish-white with a light brown head, and have a curved body covered with fine hair. Adults are attracted to light and can fly, and are about 1/8 inch long, appearing cylindrical in shape and brown in color. 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.

Indian Meal Moth Detection

Indian meal 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 Indian meal 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. The larvae are pink to dirty white in color. The larval stage looks similar to a caterpillar and crawls away from the infested foods to pupate into an adult. Often, a few larvae may be found in the packaging of the product, along with the ‘cobwebs’, cast skins, and “frass” (fecal pellets). Larvae can essentially be described as 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. The adult is easily recognizable, as it is 1/2 inch long, and has pale gray and coppery brown wings. Homeowners first recognize these small moths that fly in a zig zag fashion around various rooms, usually in the kitchen or around food, in the home. As are most moths, Indian meal moths are attracted to light and fly mostly at night in front of or near television sets. Most complaints about these moths come during the warmer parts of the year- usually the months of July through August- but 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 Indian meal 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 Fly Detection

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-rippening 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. Fruit flies are tiny- usually about 1/8 inch long, and are seen buzzing around sites of infestation. Upon closer observation, these flies are tan with large red eyes. Because the larvae are so small, they are usually not seen. 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.

FDA Regulations

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”.

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

 

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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 OR Any 1 subsample contains 90 or more insect fragments
	Rodent filth (AOAC 965.38)	Average is 1 or more rodent hairs per 100 grams in 6 100-gram subsamples examined OR Any 1 subsample contains 3 or more rodent hairs
	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

 

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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

 

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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

 

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HOPS

Insects (AOAC 967.23)

Average of more than 2,500 aphids per 10 grams

DEFECT SOURCE: Pre-harvest infestation
SIGNIFICANCE: Aesthetic

 

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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

 

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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

 

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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

 

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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

Prevention and Eradication

Prevention

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. Although, this does not exclude even the freshest products from being contaminated. Packaging especially susceptible to infestation should be inspected for tiny holes that indicate that there might be an infestation. Foodstuffs 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, and 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 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, as eggs can be laid under the lid, 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. Preventitive memthods and sanitation are the keys to avoiding an infestation or contamination of foodstuff.

Eradication

Although not seen when a product is purchased, some products have the possiblity of being infested prior to 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 be still be seen, albeit in dwindling numbers, for several weeks. First, all infested items, as well as noninfested items, must be removed from shelves, and all surfaces must be cleaned by vacuuming. After vacuuming, the bag containing the infested material must be removed and discarded. Items should be checked for beetles; 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, or simply 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 or heating the product is also%2