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Overview[]
hymenopteran, (order Hymenoptera), any member of the third largest—and perhaps the most beneficial to humans—of all insect orders. More than 115,000 species have been described, including ants, bees, ichneumons, chalcids, sawflies, wasps, and lesser-known types. Except in the polar regions, they are abundant in most habitats, particularly in tropical and subtropical regions. The order includes the best known of the social insects—ants and some species of bees and wasps. Most species, however, are solitary in habit. Hymenopterans may be parasitic or nonparasitic, carnivorous, phytophagous, or omnivorous.
Morphology[]
Adult Morphology[]
Hymenopterans are chiefly small to medium-sized insects, usually with four membranous wings and a narrow waist that sets off the abdomen from the thorax, or middle region of the body. The mouthparts may be either of the biting type or of the biting-sucking type. In the higher evolutionary forms—bees, for example—mouthparts are modified into a sucking apparatus, although many also retain biting mandibles. The ovipositor, or egg-laying organ in the female, is often very long and may be modified for piercing, sawing, or stinging. Metamorphosis is complete; i.e., the insect develops through four distinct stages: egg, larva, pupa, and adult. Sex is usually determined by whether or not an egg is fertilized, with fertilized eggs developing into females and unfertilized ones becoming males.
Behavior[]
Communication[]
Hymenoptera display an array of interesting behavioral characteristics, particularly in social species. The dancelike movements of honeybees communicate information from one individual to another about the location, distance, quantity, and quality of a particular food source. These movements were carefully studied and described by the German entomologist Karl von Frisch. Trophallaxis, or the mutual exchange of food between larvae and adults of bees,
Parasitism[]
Ants, and wasps, has been of special interest to hymenopterists. Hyperparasitism—the parasitic habit of one species upon another parasitic species—has also attracted attention. Polyembryony, the development of many individuals (as many as 1,000) from a single egg, is an unusual phenomenon occurring in some members of the families Chalcididae and Proctotrupidae. Parthenogenesis (production of young by females that are not fertilized by males) also occurs in some forms. The spider wasps (Pompilidae) usually construct single cells in the ground, in rotten wood, or in rock crevices and provision them with paralyzed spiders. The threadwaisted wasps (Sphecidae) have diverse nesting habits. Most of them nest in the ground and use leafhoppers, treehoppers, cicadas, stinkbugs, bees, winged ants, beetles, or caterpillars as food for the young, each species or group confining itself to one type of prey. Mud daubers (Sceliphron, Chalybion) build small nests of mud, often in attics, outbuildings, or eaves, and provision them with the bodies of paralyzed spiders.
Mutualism[]
Certain ants are remarkable for their relationship with insects such as aphids and scales that provide honeydew or other sweet fluids. Ants that obtain sweet fluids from the caterpillars of certain species of blue butterflies (Lycaenidae) reciprocate by allowing the caterpillars to devour ant larvae. The honey ant (Myrmecocystus in the United States, Plagiolepis in Africa) has in the nest a division of worker ants known as repletes, which are fed sugary secretions. As a consequence of high food intake, the abdomens of repletes swell into globules up to 1 cm (about 0.4 inch) in diameter.
Natural Adaptability[]
Principal differences in structure within the order include the presence or absence of wings that, when present, consist of two pairs; the presence or absence of a “waist” modifications of the ovipositor; and adaptations of mouthparts for specific eating habits. Polymorphism, the occurrence of two or more forms of a species, is highly developed in some of the social Hymenoptera. A honeybee colony, for example, contains at least one queen, plus workers and drones, with each form being structurally and physiologically different from the others.
Social castes[]
Hymenopterans range in size from the smallest fairyflies (Mymaridae), which are about 0.21 mm (about 0.008 inch) in length, to the largest of the Pelecinidae, which may exceed 5 cm (about 2 inches) in length.
Diversity[]
Bees and wasps, as the most significant agents for the pollination of flowers, are found virtually everywhere that flowering plants occur. Social species may live in colonies of as many as 1,000,000 individuals. Ants are most numerous, both in numbers and in species, in tropical and subtropical regions. The number of ant species in arctic or Alpine regions is extremely small. The group appears to be absent over great areas north of the Arctic Circle.
Economical Importance[]
The honeybee has been valued since pre-Christian times for its honey and beeswax. Beekeeping in modern times has become a lucrative and highly developed enterprise. Royal jelly, produced by honeybee workers, has enjoyed some popularity as a cosmetic, although its beneficial properties in this respect have not been satisfactorily demonstrated.
Pest Eradication[]
Certain parasitic forms are valuable control agents against insect pests. Notable among these are the parasitic wood wasps that attack wood-boring beetles; braconids that parasitize many Lepidoptera and wood-boring beetles; eulophids that parasitize scale insects; pteromalids that parasitize several crop pests; chalcids and trichogrammatids that parasitize a variety of orchard pests; and tiphiids that parasitize the Japanese beetle. Fig insects (Agaonidae) are valuable as the only pollinators of the Smyrna fig, an important crop in the Western United States.
Recent Threats[]
The fire ant (Solenopsis saevissima), accidentally introduced into the United States from South America, feeds on young plants and seeds and is known to attack young mammals. The destructive habit of legionary ants, or army ants (Dorylinae), is of particular importance in South America. Armies of as many as 1,500,000 such insects destroy almost all animal life they encounter. Leaf-cutting ants (Atta) are serious pests, especially in Brazil, where they may ravage extensive plantings of cultivated plants overnight. These insects are used locally as a source of food by people in South America.
Metamorphosis[]
Solitary Life cycle[]
The solitary wasps, of which there are about 20,000 species, usually build nests or cells, which they provision with permanently paralyzed insects or spiders. One egg is laid in each cell, and the body of the paralyzed host provides all the nutriment needed by the developing larva. Some solitary wasps nest in woody or pithy stems, whereas others dig tunnels in the soil. The mason, or potter, wasps construct nests of mud, which are sometimes vaselike or juglike and may be found attached to twigs or other objects. Sawflies, which are phytophagous, lay their eggs in incisions in plants, cut by the sawlike blades of the ovipositor. Species of several genera, notably Pontania, induce the growth of galls on willows.
Social Life cycle[]
In several families of Hymenoptera the larvae are completely dependent upon the continuous care of the adults. The colony is a family community of which every insect is an integral unit. Apart from the community, any one individual cannot properly function or survive. The essential work in the society—such as nest building, feeding and tending the brood, and defense of the nest—is performed by female workers. The fertile female, the queen, performs only one task: egg laying. The workers can be differentiated morphologically and physiologically as soldiers, outside workers, inside workers, and nest builders. The males play no part in everyday nest activities. They live only for a short time at a specific time of year, occur in limited numbers, and are virtual parasites of the colony that must feed them. The activities of certain solitary bees of the subfamily Halictinae are helpful in understanding certain aspects of the evolution of the highly organized hymenopteran societies. The females of Halictus quadricinctus survive the hatching of their own offspring. Mother and daughter stay together in the same nest, which consists of single brood cells. Thus, although each female takes care of her own cells, they build and defend the nest together. In Augochloropsis sparsalis there is a further development in that females of one nest stay together for one summer, and a division of labour occurs. Some of the young females return, still unmated, from the nuptial flight. These individuals then take charge of gathering pollen and nectar and further building of the nest and are called worker bees. The mated females merely deposit eggs.
Generations[]
The life of the honeybee colony is potentially endless. Because the queen’s honey-collecting apparatus and her pharyngeal glands and wax glands are degenerated, she is incapable of building a nest or feeding and tending the brood. The continued survival of the colony results from the fact that young queens replace the old and that queens mate with many males (a practice called polyandry) to promote genetic diversity within the colony. After their nuptial flight young queens return to the home nest. If, during the spring, many offspring develop, the colony population greatly increases, and the number of cells in the comb for developing young is no longer adequate. The colony then divides by swarming, during which the old queen leaves the nest with about half of the worker bees, and the old nest is relinquished to a newly hatched queen. The swarm finds a new nesting place and builds new combs. To make the task easier, all the departing workers consume honey before leaving the old nest.