Insects and Humans
Insects and humans
The relationship between insects and humans is long and complex. Since antiquity, insects have infected us with disease, attacked our crops, infested our food stores, and pestered our animals. And although we derive considerable benefit from their services, including pollination, honey and wax production, and the biological control of pests and weeds, the pestiferous (troublesome) activities of a mere fraction of all insect species negatively shapes humankind's perception of them. Still, throughout history insects have managed to permeate our spiritual, cultural, and scientific endeavors.
The field of cultural entomology explores the manifestation of insects in human culture. Insects have been used around the world, particularly in ancient cultures, as symbols of gods or to portend good and evil events. Their images have appeared on murals, coins, and stamps. Insects have long inspired writers, musicians, and poets—all have used their images in story, song, and verse. Artists and craftsmen still use insects as models in painting, sculpture, jewelry, furniture, and toys.
Insects in mythology, religion, and folklore
Numerous tribes around the world have used insects as totems or as symbols to explain creation myths. In the mythology of a South American tribe, a beetle created the world, and from the grains of earth that were left over, created men and women. The bizarre giraffe-like Lasiorhyncus barbicornis is one of the most grotesquely shaped weevils in New Zealand. Because of its striking resemblance to the shape of their canoes, the Maori (native New Zealanders) dubbed the weevil Tuwhaipapa, the god of the newly made canoe. Insect symbolism became even more widespread in the ancient world, especially in the Middle East. For example, hornets were symbolic of the kingdom of the first Egyptian dynasty (around 3100 b.c.), due to their fierce and threatening nature. The sacred scarab played a significant role in the religious lives of the early Egyptians. The word psyche was not only the ancient Greek word for "butterfly," but also a metaphorical reference to the soul. The ancient Greeks also used beetles, fleas, and flies in their plays and fables, such as Aesop's well-known accounting of the ant and the grasshopper. Other insects were used by the Greeks to symbolize everything from industriousness to insignificance. Early Christian animal symbolism related insects to foulness and wickedness, but eastern religions emphasizing spiritual unity with nature considered insects to signify good luck. Depictions of bees were familiar on the shields of medieval knights. Grasshoppers, beetles, and moths found their way onto the coat of arms of numerous European families. Today, modern "clans" such as college and professional sports teams have insect names or use them as mascots.
Insects in literature, language, music, and art
Scenes of honey hunting first appeared in a Spanish cave some 6,000 years ago. Later, banquet scenes depicting skewered locusts graced the walls of an ancient Egyptian tomb. In ancient Greece, images of insects appeared on jewelry and coins. Sacred scarab ornaments and other insect jewelry appeared in Egypt as early as 1600 to 1100 b. c. and were commonly worn as amulets, necklaces, headdresses, and pendants. For centuries the Japanese have carved pendants, or netsuke, in a variety of insect forms. In the Middle Ages, insects were used to adorn decorative boxes, bowls, and writing sets. Medieval monks incorporated insects in their illuminations, the brightly painted borders surrounding important religious manuscripts. The increase of geographic exploration and scientific knowledge saw insect subjects migrating to center page as part of descriptions of newly discovered species. One of the best-known references to insects in literature is in Franz Kafka's Metamorphosis, in which the lead character is transformed into a beetlelike insect. Today insect jewelry is very popular, with beetles, butterflies, cicadas, and dragonflies carved from stone or fashioned from glass and metal. The durable bodies of the beetles are used as pendants and earrings, while butterfly-wing art is commonly sold to tourists in tropical countries. Many countries celebrate insects on their postage stamps. Insects have even inspired the names of rock bands and nicknames for automobiles. They also serve as the root for such derogatory words as lousy, nitpicker, grubby, and beetle-browed. Other insects have found their way onto the big screen, inspiring fear and loathing in B-movies or providing the basis for comical, even sympathetic, characters in major motion pictures and animated features.
Insects as pests
Approximately 1% of all insect species are considered to be of any negative economic importance. Yet these relatively small numbers of species are responsible for significant economic loss as a result of their feeding activities on timber, stored products, pastures, and crops. Insects become pests as a result of a complex set of circumstances created or enhanced by concentrations of plant or animal foods. Plant-feeding insects, particularly those feeding on legumes, tomatoes, potatoes, melons, gourds, and grains, are some of humankind's greatest competitors for food. One-third to one-half of all food grown for human consumption worldwide is lost to damage caused by insects. Blood-feeding insects, such as mosquitoes and other flies, are responsible for spreading numerous pathogens, resulting in millions of human illnesses and deaths annually.
The cultivation of plants for agricultural or horticultural purposes has greatly affected how we perceive insects. Initially, crops were raised in small and widely distributed plots, resulting in small and localized pest outbreaks. But the development of large monocultures of grain (corn, rice, wheat) and fiber sources (cotton) covering vast regions during the past 150 years has resulted in a host of new insect pests. Faced with abundant, predictable, and nutritious concentrations of food in the virtual absence of natural predators and parasites, plant-feeding insects soon achieved unimaginable numbers. Once established, these pests quickly multiplied and spread, threatening economic ruin for entire regions. Every crop grown as food (for humans and their animals), as well as those grown for recreational consumption, either legally (coffee, tea, cocoa, and tobacco) or illegally (marijuana, coca, poppies) has one or more insect pests.
More than 6,000 species of thrips, true bugs, homopterans, beetles, flies, butterflies and moths, ant, wasps, and even a few termites are considered serious agricultural pests throughout the world. In some regions, the catastrophic loss of food crops as a result of locust or caterpillar depredations not only causes enormous economic harm, but can also lead to human malnutrition, starvation, and death. Large numbers of insects reduce crop yields by feeding on vegetative structures or removing nutritious fluids. Species with piercing/ sucking mouthparts (aphids, psyllids, leafhoppers, mealybugs, and plant bugs) transmit plant pathogens such as bacteria, fungi, and viruses, that reduce plant vigor. Beetles are implicated in the spread of viral diseases and pestiferous nematodes.
In temperate forests, adult and larval moths and beetles, and to a lesser extent sawfly and horntail wasps and a few flies, attack stands of living, dying, or dead trees. Although these insects form an essential part of the nutrient cycling system, their presence in trees managed for timber can quickly propel them to pest status. These insects bore into trunks and limbs, while others focus their attack on cones, seeds, foliage, buds, and roots. Living trees may suffer from reduced vitality, stunted growth, or death. In most cases, forest pests attack trees that are already under stress from lack of water, poor nutrition, or injured by disease or fire. With their impaired defense systems, trees often fall victim to plant diseases introduced by these insects.
Forest pests not only cause stunted growth, reduced yield, and lowered values of lumber and other products, but are also responsible for the loss of habitats, damaged watersheds, and increased fire hazards. Habitat disruption also leads erosion and flooding. Pest outbreaks are more likely to occur in pure stands, old growth forests, and in plantations. Ice storms, hail storms, floods, high winds, drought, disease, and fire may trigger forest-pest outbreaks.
Termites, wood-boring beetles, and carpenter ants can and do infest dry and treated timber used to build homes and outbuildings. They damage wood by feeding or continually chewing tunnels until the wood is completely hollowed out, leaving only a deceptive outer shell. Termites are the most destructive structural pests and attack timber throughout the world. While termites tunnel secretly, leaving behind only the occasional pile of frass in door and window jams, successive generations of anobiid ("death watch") and bostrichid (false powderpost) beetles clearly mark their presence with shotlike exit holes covering wooden surfaces.
Long before the appearance of humans, insects were nibbling on scattered seeds and grains, scavenging rotting fruit, hair, feathers, or decaying flesh. The moment humans began to store and process these materials for our own use, our relationship with these insects was forever cemented. The scavengers quickly adapted to living in human habitation, becoming nearly cosmopolitan (worldwide in distribution) as a result of commerce and other human activities.
The larvae of clothes moths and carpet beetles destroy woolen clothing, rugs, and hides. Powderpost beetles destroy finished wood products, damaging floorings, cabinetry, and furniture. The cigarette beetle (Lasioderma serricorne) is a serious pest of spices, legumes, grains, and cereal products. The drugstore beetle (Stegobium paniceum) attacks spices and legumes, as well as herbs, crackers, and candy. The omnivorous sawtoothed grain beetle (Oryzaephilus surinamensis) infests cereals, bread, pasta, nuts, cured meats, sugar, and dried fruits. The confused flour beetle (Tribolium confusum) is one of the most important pests of food stored in supermarkets and homes. The rice weevil (Sitophilus oryzae) infests stored cereals, especially rice; the closely related grain weevil (S. granarius) prefers wheat and barley products. Larvae of the Indian mealmoth (Plodia interpunctella) feed on coarsely ground grains, such as cornmeal (also known as "Indian" meal), as well as crackers, dried fruit, nuts, and pet food, leaving sheets of silk in their wake. The American (Periplaneta americana), Oriental (Blatta orientalis), German (Blattella germanica), and brown-banded (Supella longipalpa) cockroaches not only invade food stores, but also destroy paper products and clothing. Ants frequently invade homes in search of food and water.
Pests of domestic animals
Flies, fleas, and lice harass, weaken, infect, or kill livestock, poultry, and pets, and the damaged hides and reduction in meat, milk, egg and wool production result in economic loss. Some insect pests are quite specific when selecting their hosts, others attack many species of domestic and wild animals. Horn flies, mosquitoes, black flies, blowflies, and screwworms are all considered general blood-feeding pests. The irritating bites of female heel flies can cause entire herds of livestock to stampede. Blood-feeding horn flies and lice may feed in such numbers that their hosts suffer anemia from blood loss. Screwworm maggots live in the wounds of injured animals, where they feed on living tissues, sometimes causing death of the host. Horseflies, blowflies, and stable flies transmit anthrax and other pathogens that cause keratitis, and mastitis. Parasitic fleas and lice spend most, if not all, of their lives on the bodies of their bird and mammal hosts. Infestations of cattle lice may lead to terrible irritation and thus constant scratching against fences and posts, resulting in raw skin, hair, and blood loss. Infested animals lose their vigor and fail to gain weight. Hog lice carry swinepox and other infectious swine diseases. Flat, wingless sheep keds are parasitic flies that pierce the skin and suck the blood of sheep, causing them to rub, bite, and scratch. Some species, such as fleas, beetles, and cockroaches, are intermediary hosts of disease-causing organisms such as poultry tapeworm and heartworm, and may infect domestic animals and pets if ingested.
Vectors of human disease
Lice, flies, mosquitoes, fleas, and assassin bugs are important insect vectors of human disease. Until World War II, many more soldiers died as a result of infectious diseases spread by insects than as a result of injury on the battlefield. Houseflies are implicated in the mechanical spread of disease, and myasis, or the infection of the body with maggots, is a common medical phenomenon. Assassin bugs carry the flagellate protozoan that causes Chagas's disease.
Mosquitoes spread several viral diseases, including yellow fever and various encephalitides. They are also vectors of disease-causing nematodes and protozoans. Yellow fever and malaria infect 200 to 300 million people each year, killing approximately 2 million. The most notorious disease-spreading mosquitoes belong to the genera Aedes and Anopheles. Aedes aegypti is found worldwide in warmer regions and is the vector of yellow fever. Other species of Aedes are associated with dengue, eastern and western encephalitis, and Venezuelan equine encephalitis. Several species of the widely distributed Anopheles are vectors of malaria.
The tsetse are biting, blood-feeding, African flies and are efficient vectors of African sleeping sickness in humans and nagana in animals, diseases caused by a parasitic trypanosome. Although tsetse prefer other animals as hosts, they frequently bite humans. Historically, sleeping sickness dramatically retarded the exploration and settling of much of the African continent. Although sleeping sickness is usually under control in most regions, nagana remains an important and widespread disease.
Fleas ingest the plague-causing bacterium by feeding on infected rodents. As the rodents die from the disease, the fleas bite humans to feed, passing on the bacterium to their new host. Bubonic, pneumonic, and septicemic plague are all forms of the plague. Bubonic plague, or Black Death, was responsible historically for the deaths of millions of people in Europe, Asia, and Africa. Although plague is treatable today with antibiotics, future pandemics are still likely. With increased bacterial resistance to antibiotics, the specter of resistant strains of the plague-causing bacterium remains a deadly possibility. Oriental rat fleas also spread endemic typhus.
Outbreaks of the body louse can reach epidemic proportions in elementary schools and military posts. These lice are vectors for the rickettsial disease epidemic typhus. Unlike mosquitoes, the lice do not inject their host with the pathogen. Instead, human hosts infect themselves by crushing lice at the bite site, or by exposing their eyes, nose, and mouth to the feces of infected lice. Typhus is fatal to body lice. They pick up the disease from the blood of an infected host and soon die, but not before they can infect others.
Controlling insect pests
Today, many pests are effectively controlled by a system known as integrated pest management (IPM). IPM programs entail a combination of chemical, mechanical, cultural, physical, or biological controls. These methods are augmented by legislation mandating proper pest-control procedures, implementing quarantines of plant and animal hosts, and certifying pest-free imported and exported agricultural commodities.
Effective pest control, whether in the home, forest, or farm, is absolutely dependent upon the correct identification of the insect and a knowledge of its life cycle. Armed with this information, pest-control efforts can be directed at the pest's most vulnerable stages of development. Even closely related species can have slight differences in biology that can render useless methods designed to control their relatives. Knowledge of a pest's biology, coupled with thorough and regular survey and detection programs, frequently enable the implementation of preventive measures before pest populations cause serious economic damage.
Chemical controls can attract, repel, or poison pests. They are used in traps or applied as dusts, granules, sprays, aerosols, and fumigants. Systemics penetrate plant tissues, killing only the insects that feed on the plants. Chemical insecticides include inorganics, oils, botanicals, and synthetic organophosphates. These compounds act as physical poisons, killing the insects by asphyxiation or by abrasion that causes the loss of body fluids. Protoplasmic poisons precipitate proteins, while respiratory poisons deactivate respiratory enzymes. Many commonly used insecticides, including parathion, pyrethrins, and dichlorodiphenyltrichloroethane (DDT), are nerve poisons. Abuse of insecticides, especially those that persist in the environment such as DDT, can and do lead to catastrophic declines in predators that rely directly or indirectly on insects as food. Insect resistance to pesticides, which can occur in a matter of generations, may preclude the usefulness of chemical applications.
Mechanical and physical controls directly affect the insects or their environments. Labor-intensive methods such as hand picking, trapping, and barriers are often impractical on a large scale. Exposing storage containers to extreme temperatures will reduce insect populations in grain elevators, while soaking plant bulbs in warm-water baths kills some pests infesting nurseries.
Cultural controls involve the utilization of various agricultural practices to reduce insect pest populations and require extensive knowledge of the pest's life cycle. Crop rotation prevents the buildup of pest populations over time, as does the careful selection of mixed crops. Small, expendable plantings known as trap crops are planted to lure pests away from major crops. Once infested, these crops are treated with pesticides, plowed under, or both. Tillage reduces populations of soil insects by eliminating their host plants, exposing them to dry air and predators, or crushing them. Clean culture is the removal of all crop residues, leaving nothing behind for pests to lay their eggs on or to eat. Changing planting and harvesting times to reduce crop exposure to pests can also be effective. Genetically altered crops, although controversial, may be less attractive to pests or more tolerant of pest damage. Some possess insecticidal qualities or lack essential nutrients required by pest species.
Insect populations may be naturally or biologically controlled by a host of "checks and balances." When a species becomes established outside its natural range, it may achieve pest status because its normal population controls did not also become established. This same disruption may occur when a species encounters an unlimited food supply in the highly disturbed ecosystems typical of the monoculture practices of modern agriculture. Entomologists are then deployed to find the geographic origin of the pest and to identify its naturally occurring predators, parasites, and pathogens. These "biological control" organisms are then selected for the host specificity, effectiveness, ease of rearing, and ability to adapt to their host's new environment. Typically, successful natural or biological control is marked by closely synchronized fluctuations between prey and predator populations. Pest outbreaks are followed by heavy predation followed by prey scarcity that depletes the predator population. The goal of biological control programs is not to eradicate the pest, but to keep populations below levels at which they are economically damaging.
Pest control of any kind has its risks and may adversely affect other species or their habitats. Biological control is based on the fact that the introduction of alien organisms will disrupt established populations. Tests are usually conducted to determine whether introduced organisms will adversely affect nontarget organisms, but extensive investigations of the delicate balance between pests, their natural enemies, and other insect species in the community are seldom practical and difficult to assess. In some cases, species introduced as biocontrols, such as the marine toad into Australia to control sugar cane beetles, have become part of the much larger problem of alien species invasions, a major factor in local and species-wide extinction.
The dislike of humans for insects is understandable, as they bite, sting, invade our homes, infest our food, and ravage our gardens and crops. But for some, this dislike is replaced by an intense, irrational fear called entomophobia. Entomophobia in childhood usually develops in both sexes, but if developed in adulthood occurs mostly in women. Entomophobes not only fear insects, but also the places where they might occur, and avoiding contact with insects can be quite problematic given the animal's universality. As with those who suffer other phobias, entomophobes experience typical fright responses such as an increased heart rate, sweating, labored breathing, tremors, and dizziness, as well as temporary paralysis or running away. Entomophobia (and other phobias) may develop as a result of innate fears regarding threatening objects or situations, or genetic predisposition. Treatment may include psychoanalysis or modeling therapy, in which a therapist, friend, or relative touches an insect in the presence of the entomophobe.
Delusory parasitosis, or Ekbom's syndrome, is when a person is under the false illusion he or she is being attacked by insects or other parasites. Sufferers typically seek help from entomologists and pest-control operators, rather than qualified mental health care professionals, convinced that "bugs" are burrowing under their skin. Sufferers, often middle-aged men and menopausal women, subject themselves to caustic fluids and compounds to rid themselves of the imagined pests, or mutilate themselves with knives or razors in an effort to dig them out. Friends and relatives are sometimes so convinced of the veracity of the sufferer's condition that they develop sympathetic itching.
The scientific study of insects
Entomology is the science of insect study. Entomologists around the world observe, collect, rear, and experiment with insects, either for purely scientific or for practical reasons. Regardless of the approach, the basis for useful and accurate entomological work is insect classification. Taxonomy, the
science of naming things, is one of the basic elements of insect study. Unlike common names, which can vary considerably between regions, cultures, and languages, scientific names are universally recognized. Papers published around the world in different languages all use the same scientific names for the same species. The use of this universally recognized system greatly facilitates the storage and retrieval of biological information. Efforts to standardize common names are usually applied only to economically important insects.
Insect systematics is the study and ordering of the natural diversity of insects. The discipline blends taxonomy with information from other fields of biology, such as morphology, behavior, genetics, biogeography, phylogenetics, and DNA sequencing, to arrive at a classification that reflects the evolutionary paths of insects. Systematics also contributes information used in other insect studies, including faunistics, the study of some or all insects in a region; ecology, the study of insect interrelationships with their environment; and zoo-geography, the study of insect habitats and distributions, past and present. Insect distributions based on detailed faunistic and taxonomic studies provide clues to the nature and extent of past climates. The fossil remains of insects whose species or genera are extant today, combined with information on their current habitat requirements, can be used with a considerable degree of confidence to infer ancient ecological conditions that prevailed tens or hundreds of thousands of years ago. The validity of these and other conclusions all depend on the quality of current systematic knowledge. Systematic data is also critical to our ability to conserve insects threatened with extinction and to preserve their habitats. Laws and regulations drafted by legislators and other administrative bodies to protect sensitive species are more likely to succeed if they are based on systematic information that accurately reflects the biology, distribution, and habitat requirements of the insect.
There are a number of entomological subdisciplines. Forensic entomologists examine insects found at crime scenes to determine such facts as time and place of death, and also investigate infestations of food and materials to determine liability. Forest entomologists track the depredations of insects attacking managed timber. Economic entomologists focus their attention on controlling pest species that attack gardens, crops, vineyards, and orchards. Medical and veterinary entomologists study insects as vectors of disease. As humans continue to modify and destroy habitats, we increase our contact with insect vectors, increasing the frequency and importance of insect-borne diseases that afflict both humans and animals. Battling diseases, such as the West Nile virus, that affect humans, domestic animals, and wildlife will require the close cooperation of researchers in the biomedical and veterinary sciences. Conservation medicine connects these two fields of endeavor to explore the links between wildlife species and the health of ecosystems and people. By pinpointing environmental sources of pathogens, scientists can begin to understand the ecological causes of changes in human and animal health, and entomologists will make significant contributions to the development of this field.
The human benefits derived from insects are enormous, not only as objects of pure scientific interest, but also for the services and products they provide. They not only pollinate crops, but also directly produce food, fiber, and other useful products. Insects are an important source of nutrition and income in many parts of the world. They also help control pest species, reducing our dependence upon chemical controls. Insects provide educators with a rich and diverse template from which they can introduce students to the natural world and provide scientists with sensitive ecological indicators.
Insects are the most important animal pollinators. Brightly colored flowers with highly attractive odors draw insects seeking nutritious pollen and nectar. Pollen is an excellent source of protein; nectar is high in carbohydrates. The relationship between flowers and insects is one of mutualism: angiosperms provide insect pollinators with food, while the insects are essential to the propagation of the angiosperms. Insects in at least 29 orders participate in pollination. Although many flower-visiting insects focus their attention on pollen and nectar, others eat part or all of the inflorescence.
The effectiveness of pollinators of agricultural crops, especially bees, is determined by their host-plant specificity, foraging distance, daily foraging period, prevailing temperature and humidity, number of flowers visited, and pollen-carrying capacity. Although those honey bees managed in association with extensive monoculture are effective pollinators, solitary native species or other social bees are frequently better adapted for pollinating orchards and other crops. Bumblebees are used to pollinate greenhouse tomatoes in North American and Europe and are the sole pollinators of red clover. New Zealand has imported "long-tongued" bumblebees to increase their red clover yields with great success. In Europe, flies are the most effective pollinators of special varieties of cabbage and other cruciferous crops.
In Japan, fruit growers used bundled hollow reeds as artificial nests to encourage the pollination activities of Japanese horn-faced bees (Osmia cornifrons) with spectacular success. This solitary species has since been imported into the United States for orchard-fruit pollination. The European alfalfa leaf-cutter bee (Megachile rotundata) has been imported to facilitate alfalfa pollination. Small colonies of the native social Alkali bee (Nomia melanderi) have also been used in some parts of the United States as pollinators. These and other solitary bees are not as easily manipulated as honey bees, but their use as pollinators in commercial crops is increasing.
Oil palms, natives of West Africa, were imported into Southeast Asia as a major plantation crop, but with limited success. Outside their natural range, oil palms had to be pollinated by hand. Entomologists searched oil palms in West Africa and soon discovered a complex of beetles, mostly weevils, responsible for their pollination. One species was imported to Malaysia, where its establishment has resulted in consistently higher yields of oil palms.
Apiculturists, or beekeepers, manage colonies of bees that have been selected for their docility and foraging capability. The bee genus Apis consists of four species in Europe and Asia, of which one, A. mellifera, is widely kept by humans for their honey and wax production. For centuries, honey was the only sweetener available to Europeans, and fermented honey was used to make wine such as mead in Europe and tej in Ethiopia. The antiseptic qualities of honey also made it useful as a dressing for wounds. Artists and sculptors have long used beeswax to cast and mold sculptures, construct masks, and to build models. Beeswax was also used in ointments, suppositories, cosmetics, candies, lubricants, adhesives, varnish removers, and furniture and shoe polishes, but has been supplanted by paraffin. The pollination services of honeybees are just as valuable as their production of honey and wax. Beekeepers transport millions of hives each year in an effort to market their bees' pollination services and to ensure a continuous supply of pollen and nectar for them throughout the season.
Early beehives in Greece were made of clay pottery, while those European and Africa were made of hollow logs. Later the Europeans began using dome-shaped beehives constructed of woven straw. Modern hives first appeared in or around 1850 in the United States and Europe. These bee enclosures consist of a stack of boxes, each with frames suspended inside that serve as a foundation for the waxen honey and brood comb. The brood capacity of each hive is expanded throughout the season by adding new boxes and frames. The bees usually store their brood in the deeper boxes below, while keeping honey in the shallower boxes and frames above. In temperate regions, the bulk of the honey, up to 222.5 lb (100 kg) per box is harvested annually. The bees are fed a sugar solution at regular intervals during the late summer and throughout the winter.
Other valued bee products include wax, royal jelly, new swarms, and propolis. The latter is a resinous material collected
by foraging bees and is used to attach combs to the roof of the hive. It has antibiotic qualities and has been claimed to successfully treat some human ailments. Royal jelly is high in protein and vitamins. It is fed to all larvae for the first five days, but only those destined to be queens receive it until pupation. Pollen has many therapeutic properties and is reported to alleviate the symptoms of colds, influenza, asthma, hay fever, arthritis, rheumatism, prostate disorders, and menstruation and menopause, as well as to enhance virility. Pollen treatments often involve ingesting a mixture with unrefined honey or propolis. In Eastern Europe and Western Asia, areas with intensive apiculture, people frequently live to be 100 years or older. Unrefined honey, including bits of wax, pollen, and propolis, is a regular component of the local diet. However, the precise value of these components, and their relationship to longevity, remains unclear.
Commercial silk is harvested primarily from cocoons spun by the silkmoth (Bombyx mori), also known as the Oriental silkworm or the mulberry silkworm. The silk is produced by the salivary glands of the larvae, or silkworms. A native of China, the silkworm is the world's only completely domesticated insect; none are known in the wild. In other parts of China, Africa, and India, cocoons of other moth species are first collected in the wild before the silk can be harvested.
The earliest records of sericulture date back to 2600 b. c. Raw silk became an important item of trade between China and Europe. The Silk Road, opened in a. d. 126, stretched westward nearly 6,000 miles across China, Turkestan, and Iraq, before ending at the northeastern shore of the Mediterranean Sea. China carefully guarded its silk industry for centuries, but about 150 b. c., eggs were smuggled out of the country and into India. In a. d. 300, the Chinese sent four women to Japan to instruct their royal court in the art of sericulture, establishing what would become the world's largest silk industry. In a. d. 555, two European monks smuggled silkworm eggs and mulberry seeds out of China, marking the beginning of sericulture in the western world.
Sericulture is widely practiced today. China and Japan remain the largest producers of silk, but thriving silk industries are found in South Korea, Indonesia, Brazil, Thailand, and Uzbekistan. China accounts for about 80% of the world's raw silk production. Once the largest producer of silk, Japan is now the world's largest consumer, its market driven by the manufacture of kimonos. Italy is the largest producer of silk in Europe, while the United States is the largest importer. The present value of silk production around is estimated at more than $1 billion.
Raising silkworms is incredibly labor intensive. About 1,700 cocoons are required to make one dress; and their caterpillars must consume 125 lb (56.7 kg) of mulberry leaves before pupation. Just one pound of caterpillars can consume 12 tons (10.9 t) of mulberry leaves before reaching the pupal stage. The larval host plant, mulberry, is easily and widely grown, but most caterpillars in Japan are reared on a completely synthetic diet. Silkworms are susceptible to various maladies. Interestingly, the investigation of one of these diseases ultimately led the French microbiologist Louis Pasteur to correctly deduce the microbial origin of diseases.
To harvest the silk, mature caterpillars are transferred to a rack where they can spin their cocoons before pupating inside. The cocoons are then boiled to kill the pupae within and to remove the sericin, a dull and chalky outer coating. The ends of the silk filaments from several cocoons are located, unraveled, wound together, and attached to a spool. The number of filaments attached to the spool determines the size of the thread. The spools of raw silk are then soaked and dyed before they are reeled onto skeins. The skeins are bundled into books, which are gathered into bales and shipped to mills for weaving.
Apiculture and sericulture were the earliest forms of insect farming. Today, other insects are reared in captivity for commercial, research, and biocontrol purposes. Insect farms may be small-scale operations or massive commercial enterprises. Cockroaches, grasshoppers, crickets, fly maggots, blood-worms, fruit flies, mealworms, and other insects are regularly reared throughout the world as live pet food, fish bait, research subjects, and educational tools. Still others are mass reared to combat weeds and insect pests.
Butterflies and other insects are raised around the world and shipped live to insect zoos and butterfly houses, research facilities, or preserved for the dead-stock trade. Most specimens are used as ornaments or in decorative displays. Hobbyists and researchers requiring quality specimens also drive a significant portion of the dead-stock trade. The sale of preserved insects, mostly beetles and butterflies, amounts to tens of millions of dollars annually.
Butterfly farms, established in Central and South America, Malaysia, and Papua New Guinea, have been regarded as a benefit to butterfly conservation because they do not rely on specimens caught in the wild to supply the commercial demand for living and preserved specimens. Butterfly farmers enclose their breeding colonies with shade cloth to protect the stock from parasites and predators. Some pupae are shipped live, others are kept until they reach adulthood. After the butterflies emerge, some are released to enhance local wild populations, while the remainder is packaged for sale. Proceeds from the sales are used to support families, maintain the farm, and to preserve or enhance the environment that replenishes the breeding stock.
Insects as biological controls
Biological control, or biocontrol, is the augmentation of naturally occurring enemies of a pest to reduce or eliminate the reliance on expensive and potentially ecologically disastrous pesticides. Another form of biological control involves irradiation to produce large numbers of sterilized male insects, such as fruit flies and screwworms, for release. When combined with cultural practices, mechanical controls, and carefully managed use of insecticides, biological control is an important component of any IPM program.
Numerous predatory and parasitic insects are commercially reared for use in biological-control programs in greenhouses, fields, and orchards. Parasitic wasps are routinely released worldwide to control plant-feeding pests such as moth caterpillars, aphids, and scale insects. After some early and well-documented successes, the widespread introduction of ladybird beetles (or ladybugs) to control aphids and scales has achieved mixed results. Although most insect biocontrols target garden and agricultural pests, others attack medical and veterinary pests or weeds. For example, cactus-feeding moths, scales, and beetles have been imported into Australia and parts of Africa to control invasive cacti.
Insects as food
Insects are an excellent source of fat and protein and were no doubt a staple in the diet of early hunter/gatherers. Today, eating insects, or entomophagy, is widely practiced. Throughout tropical Africa, people invade termite mounds for the large queens and eat them on the spot. The queens' swollen, egg-filled abdomens (the size of a breakfast sausages) are an extremely rich source of fat. Another caterpillar, the mopane worm (Imbrasia belina) is regularly harvested in southern Africa, where it is dried and eaten like a cracker or soaked in tomato sauce. Large grasshoppers are commonly eaten in parts of Africa and Asia. In Thailand, locusts are roasted and eaten on satay sticks, while giant water bugs are roasted or soaked in brine and eaten like crackers. June beetles, weaver ants, and mole crickets are eaten in the Philippines, and adult and larval weevils and scarab beetles are consumed in parts of Asia and Australia. Australian aborigines eat a wide variety of insects, including the well-known cossid moth larva known as the witjuti or "wichety" grub. The aborigines also excavate nests of honeypot ants in search of the nectar-filled ants known as repletes. A different genus of honeypot ant is known from western North America, where some rural Mexicans also dig them up for food. Western European culture has largely ignored insects as food, although they appear regularly as a curiosity at entomological gatherings and some eateries. Given their nutritional value, abundance, and diversity, the commercial opportunities afforded by the development of insects as food are boundless.
The plethora of defensive chemicals, mating pheromones, toxins, and other compounds produced by insects undoubtedly have a therapeutic value and, as with botanicals, their early use as "folk medicines" should not lessen their prescription or discourage further research. The real or imagined benefit of using insects as medicine probably developed as a result of their consumption as food. Various insects were burned, roasted, and pulverized into numerous concoctions purported to have some curative effect. Early Europeans used powdered ladybird beetles to relieve toothache and to cure measles and colic. Whirligig and rhinoceros beetles were used in preparations to increase the libido, and one Javanese click beetle is the primary ingredient of a particularly sexually stimulating potion. Japanese folk medicine incorporated species from several families of beetles to treat conditions as varied as convulsions, cancer, hydrophobia, and hemorrhoids.
In Medieval Europe, concoctions derived from insects were thought to transfer their outstanding qualities to the patient, and thus conspicuously hairy bees and flies became ingredients in hair tonics and baldness cures. Singing crickets and katydids were recommended to treat disorders of the ears and throat. Earwigs were prescribed for earache, perhaps because of their fan- or ear-shaped hind wings. Wasp galls were pressed into service as treatment for hemorrhoids; simply carrying one in a pocket was all that was required. Even today in parts of Latin America and Asia, the ingestion of large, powerful horned beetles is thought to impart the same robust qualities to the consumer. As far as is known, any therapeutic effects achieved by these treatments were attained entirely through the power of suggestion!
Insect defenses have been adapted and exploited for pharmaceutical use. Bee stings have long been used to treat patients with rheumatism, as the venom acts to increase blood flow to the afflicted areas while simultaneously stopping pain. Several commercial preparations using bee venom are sold today. Cantharidin, a blistering defensive compound found in the bodily secretions of blister beetles, renders them distasteful to predators. Cantharidin is highly toxic to humans if ingested; 30 mg is lethal. In smaller doses, cantharidin can cause severe gastroenteritis and irreversible kidney damage. In spite of its toxicity, cantharidin extracted from the European Spanish fly (Lytta vesicatoria) and other blister beetles has been used to treat epilepsy, sterility, asthma, rabies, and lesions resulting from gonorrhea. Lytta vesicatoria is best known for its purported qualities as an aphrodisiac, which were first noted in the sixteenth century. Today pharmaceutical catalogues mention cantharidin for use in some ointments and plasters, the preparation of tinctures in veterinary medicine, and an ingredient in some hair-restorers. In Peru, warts are scarified, then covered with a pulp made from blister beetles. A blister forms over the wart, and after several days of treatment, the wart is destroyed.
During the Napoleonic Wars and the U. S. Civil War, military surgeons noted that untreated soldiers with deep wounds infested with maggots healed more quickly and in greater numbers than their treated comrades. During World War I, it was discovered that some wound-infesting maggots consumed only dead tissue. As they fed, the maggots excreted large quantities of the nitrogenous substance called allantoin that acted as a sterilizing agent. For years surgeons have employed maggots carefully raised under aseptic conditions to clean deep wounds, especially those filled with pus or associated with bone fractures. However, synthesized allantoin and the use of antibiotics have rendered maggot therapy all but obsolete, except in the most extreme of cases.
Ants and beetles with large, piercing mandibles have been used as crude sutures to close wounds. The insects are held up to the edge of the wound and allowed to bite the skin, bringing the two sides together. The heads are then separated from the body and left in place until the wound has healed. As mentioned earlier, antiseptic honey has been used to dress wounds, while sterile and inert beeswax is used in some orthopedic surgeries to fill spaces in bones.
Other products produced by insects
Several species of scale insects and their relatives have been used for centuries to produce varnishes, dyes, and inks. Shellac is a sticky, resinous material produced as a shell-like coating by the lac insect (Laccifer lacca), native to India. These insects live in small groups, encrusting twigs of acacia, soapberry, and fig. Twice each year, the twigs are gathered and the insects scraped off. Bright red lac dye is then extracted from the body tissues of the female with hot water, while the resinous "shelllac" is melted and filtered. The shelllac eventually cools, forming the flaky texture of commercial shellac. Because of its elasticity, resistance to solvents, adhesive properties, and insulative qualities, shellac is used in furniture and shoe polishes, printing inks, electrical insulators and sealants, clothes buttons, and a variety of hair-care products. Before compact discs and vinyl albums, shellac-based records were the standard in the recording industry. India exports 50.7 million lb. (23 million kg) per year, mostly to Europe and the United States.
The red dye cochineal is produced from the dried and pulverized bodies of the cactus mealybug, or cochineal insect (Dactylopus coccus). The pigment is repugnant to the insect's predators and probably deters parasites. Feeding exclusively on cactus, the cochineal insect is distributed from southwestern United States to South America. The Pima Indians of Arizona and the Aztecs of Mexico cultivated and used these insects as dye. The Spanish explorer Hernando Cortez was the first westerner to report the use of cochineal, and the intense vermilion dye soon became an important item in European commerce. Spain's monopoly of cochineal was eventually broken, and imported scales and their cacti were soon raised throughout the Mediterranean region and in India and Australia. However, despite the efforts in these various locales, the insects managed only to establish themselves in the Canary Islands. To produce cochineal, the insects are scraped off the cactus and killed in boiling water, which also removes their waxy coating. The bodies are dried in the sun and then ground into a powder. Approximately 70,000 insects are needed to produce 3 lb (1.36 kg) of powder, or 1 lb (0.45 kg) of cochineal. The importance of cochineal has declined with the increased use of synthetic dyes, although it still enjoys some popularity as a natural food coloring in Latin America and in some soft drinks. Its use in cosmetics is complicated by the fact that Orthodox Jews do not consider cochineal insects kosher. Today Peru and the Canary Islands are the principal producers of cochineal.
Insects as bioindicators
Researchers use insects as indicator species to measure environmental disturbances, the effects of habitat fragmentation, and changes in biodiversity. The responses of some sensitive insects to habitat disturbances are rapid, predictable, and easily analyzed and measured. For example, aquatic beetles and the larvae of mayflies, stoneflies, dragonflies, and damselflies are especially sensitive to even subtle changes in water temperature, chemistry, and turbidity. The presence or absence of a particular species may indicate habitats polluted as a result of illegal chemical dumping, agricultural and mining runoff, effluent from power plants and sewage treatment, or increased erosion as a result of logging. Careful monitoring of aquatic insect populations can signal problems long before pollutants manifest themselves in plant and vertebrate populations. Changes in some terrestrial insect populations, especially those species with high ecological fidelity, are used to measure changes in plant communities, such as those affected by urban and agricultural development. Soil-dwellers have long been used to indicate soil fertility and levels of pollution. The presence of easily identifiable, taxonomically well-known, and intensively studied species, such as butterflies and tiger beetles, are also used to identify significant ecological habitats worthy of protection.
Insect populations are subject to decline, extirpation, and extinction, primarily as a result of habitat loss. Urbanization, agricultural development, water pollution and impoundments, wetland modification, exotic introductions, and pesticides have all been linked to the decline of some species. Even lesser-known, although no less significant, phenomena such acid rain, electric lights, and off-road vehicles exact a toll on insect populations. Collecting, although touted by some as a significant threat to localized species, has never been shown to result in the extinction or extirpation of populations. Nonetheless, collecting large numbers
of specimens from a single population is considered unethical by many entomological societies, and is stated as such in their guidelines. The Xerces Society, based in the United States, is the only international organization dedicated solely to the conservation of all invertebrates, including insects. Several European countries publish catalogues of sensitive, threatened, or endangered species known as Red Lists, and other national organizations sponsor insect-conservation programs that include the formulation of plans for habitat management and restoration and captive breeding, and reintroduction programs.
Most legislative efforts to conserve insects have been directed at butterflies and beetles, although other insect orders receive some recognition. Internationally, the Convention on International Trade in Endangered Species (CITES) monitors the importation and exportation of listed species. The Endangered Species Act (ESA) of the United States is a comprehensive legislative effort, not only to list and protect threatened and endangered species, but also to provide for the preservation of their habitat. In Papua New Guinea, laws protect some species, regulate the sale of others, and preserve important habitats. The collection and sale of Papua New Guinea insects may be sanctioned only by a government marketing board known as the Insect Farming and Trading Agency. National parks and wildlife reserves may have laws protecting all wildlife in their jurisdiction, including insects. Other local, state, or provincial agencies also protect insects. Many species are afforded protection because they occur in small populations living in highly restricted or sensitive habitats, such as caves or sand dunes.
Insects as educational tools
Insects afford primary, secondary, and college students an inexhaustible resource that stimulates curiosity and provides important insights into the biological world. Processes found in all animals, such as growth and reproduction, are easily observed in insects. Their relatively short life cycles and dramatic physical transformations during the growth process make them ideal subjects for classroom and laboratory study. They are readily available, inexpensive, easy to maintain and handle, and their use seldom raises the ethical issues associated with using vertebrate animals. Outdoor environmental education with insects provides students with opportunities to study and observe food webs, especially pollination and predator-prey relationships. In addition to numerous field guides, there are numerous instructional materials available, particularly at the primary and secondary levels.
High schools and universities dissect large numbers of cockroaches and locusts to study morphology and physiology. Fruit flies have been used in genetic research for decades and are excellent models for students studying inheritance, as the giant chromosomes found within their larval salivary glands are easily observed. Adult features, such as eye color and wing length, are easily recognized and used in simple breeding experiments. Ants and crickets demonstrate pheromone and acoustic communication systems, respectively. Dissections of mud dauber wasp nests provide opportunities to observe such ecological interactions as parasitism and nutrient recycling. Mealworms (Tenebrio molitor) and tobacco hornworms (Manduca sexta) provide insight into complex behaviors resulting from competition and overcrowding. Madagascan hissing cockroaches (Gromphadorhina portentosa) make excellent research subjects for studies of communication, dominance hierarchies, and learning, while mantids offer fascinating opportunities to observe growth, development, and predatory behavior.
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Arthur V. Evans, DSc