HYMENOPTERAN

a member of the insect order Hymenoptera, the third largest of the insect orders with more than 110,000 species of bees, ants, sawflies, ichneumons, wasps, chalcids, and horntails. Because of the preponderance of plant pollinators and insect parasites in the group, it is probably the most economically important order of insects. Hymenopterans are found throughout the world except in the polar regions, and they are especially abundant in tropical and subtropical regions. The first hymenopterans appeared possibly as early as the end of the Permian Period (about 225,000,000 years ago), and were certainly in existence by the middle of the Jurassic Period (150,000,000 years ago). The first bees appeared during the Miocene epoch, which began some 26,000,000 years ago and lasted about 20,000,000 years. Hymenopterans range in size from the fairyflies (Mymaridae), which are only 0.21 millimetre (0.008 inch) long, to the Pelecinidae, which can exceed 5 centimetres (2 inches), but most members of the order are under 2.5 cm long. The order is divided into two suborders, the Symphyta (sawflies and horntails) and the Apocrita, which consists of several superfamilies including the Chalcoidea (chalcids), Cynipoidea (gall wasps), Scolioidea (ants and parasite wasps), Vespoidea (paper and potter wasps), and Apoidea (bees). As in other insects, the adult hymenopteran body includes three regions: head, thorax, and abdomen. Most hymenopterans have a narrow waist dividing the abdomen from the thorax. Membranous wings are present in most species; when they occur there are two pairs, and the anterior pair is the larger. The wings are interlocked by tiny hooklets along the anterior edge of the hindwings. The mouthparts are adapted for biting or for sucking. Two large compound eyes are present, as well as (usually three) simple eyes, or ocelli, located on top of the head. The structure of the antennae varies widely, but they are typically of moderate length or occasionally longer than the body. Various bees have pollen-carrying structures (scopa); these may be basket-like webs of long hairs on the legs or ventral abdomen. The ovipositor is at the tip of the abdomen. In sawflies it is sawlike, for slitting the plants in which these insects lay their eggs. In all remaining hymenopterans it is adapted for piercing or stinging. Many bees have wax glands on the ventral part of the abdomen. This wax is used to construct combs for housing the brood and storing nutrients. In the hymenopterans the senses of vision and smell reach their most advanced development within the class Insecta. Bees are sensitive to light of various wavelengths, including ultraviolet. They are able to orient themselves by means of the Sun (even on cloudy days owing to their sensitivity to polarized light) and by various visible landmarks. The sense of smell is used by guard bees, which check every individual entering the hive to make sure it has the correct colony odour. Ants leave scent marks to find their way back to the nest. Many hymenopterans use scent to find mates. Hymenopteran larvae generally have a head, a 3-segment thorax, and an abdomen composed of 9 or 10 segments. In the suborder Symphata the larvae are typically caterpillarlike, with six legs on the thorax and more on the abdomen, except for the wood- and stem-boring forms, which lack abdominal legs. Larvae of the Apocrita typically lack legs and resemble maggots. Bees and wasps can be found anywhere flowering plants occur. Few ant species are found in colder climates, but in the tropics there is a great abundance and diversity of ants. Some hymenopterans, such as sawflies and bees, are phytophagous (plant-eating). Others, including various wasps and ichneumons, are parasitic on other insects. South American army ants (Dorylinae) eat any plant or animal food that they find. Some groups, including many wasps, sawflies, and some bees, are solitary. Others, including all the ants and many advanced bees, are among the most well-known social insects. Most solitary wasps, of which about 20,000 species are known, provision their nests with paralyzed insects or spiders. They place one in each cell containing an egg, and the larvae thus hatch with a ready food supply. Females of the parasitic superfamily Ichneumonoidea leave their eggs in or on the larvae of various insect hosts. The social insects form colonies in which each individual has a well-defined role, and individuals of these species usually do not survive for long when separated from their colonies. The colonies of advanced species have a reproductive female, or queen, plus various other physiologically or behaviourally distinct types to maintain the colony. The majority of colony workers are nonreproductive females; males are necessary only for a brief mating period each year. The female workers build and defend the nest and care for and feed the brood; they may or may not be morphologically differentiated into builders, soldiers, inside workers, and outside workers. In the honeybee there are no different morphs (body types) for these jobs; rather, the division of labour is based on age group. Honeybees have evolved a mode of communication by which they can pass information to their hive-mates through dance-like movements. The duration, angle, and direction of the dance can tell the other bees the quantity and quality of a new food source as well as its distance and direction. When a hive becomes overcrowded the old queen will take half of the population and seek a new nesting site. Scouts are sent out from the swarm, and when they return they use a similar dance to describe the location and potential of any sites they have found. Various hymenopterans are important to man. Bees and other species are among the most important pollinators of flowering plants, and the honeybee has long been cultivated for both honey and beeswax. Various parasitic forms are valued as controls on insect pests: wood wasps, for example, parasitize wood-boring beetles; eulophids parasitize scale insects; and tiphiids parasitize Japanese beetles. The larch sawfly (Pristiphora erichsonii), European spruce sawfly (Gilphinia), and wheatstem sawflies (Cephidae) are among the few hymenopterans that are serious economic pests. Bumblebee (Bombus) Sawfly (Cimbex) any member of the order Hymenoptera, comprising the third largest and perhaps the most beneficial to man of all insect groups. More than 110,000 species have been described, including ants, bees (see photograph), ichneumons, chalcids, sawflies (see photograph), wasps, and lesser known types. Except in the polar regions, they are abundant in most habitats, particularly in tropical and subtropical regions. Collectively, the Hymenoptera are most important to man as pollinators of wild and cultivated flowering plants, as parasites of destructive insects, and as makers of honey. The Hymenoptera are divided into two suborders: Symphyta (mainly sawflies and horntails) and Apocrita (wasps, ants, bees, and most parasitic forms). The order includes the best known of the social insectsants and some species of bees and wasps. Most species, however, are solitary in habit. Hymenopterans may be parasitic or nonparasitic; carnivorous, phytophagous, or omnivorous. Additional reading General works K.V. Krombein et al., Hymenoptera of America North of Mexico (1958); Catalog of Hymenoptera in America North of Mexico, 3 vol. (1979). Evolution S.I. Malyshev, Genesis of the Hymenoptera and the Phases of Their Evolution (1968; orig. pub. in Russian, 1966). Social insects C.D. and M.H. Michener, American Social Insects (1951); D.W. Morley, The Evolution of an Insect Society (1954); W.M. Wheeler, The Social Insects: Their Origin and Evolution (1928); E.D. Wilson, The Insect Societies (1971). Specific taxonomic groups C.H. Andrewes, The Lives of Wasps and Bees (1969); W.S. Creighton, The Ants of North America (1950); H.E. Evans, The Comparative Ethology and Evolution of the Sand Wasps (1966), and Wasp Farm (1963, reissued 1985); M. Lindauer, Communication Among Social Bees, 3rd ed. (1971); T.B. Mitchell, Bees of the Eastern United States, 2 vol. (196062); C.R. Ribbands, The Behaviour and Social Life of Honeybees (1953, reissued 1964); K. von Frisch, The Dance Language and Orientation of Bees (1967, reissued 1993; originally published in German, 1965); W.M. Wheeler, Ants: Their Structure, Development and Behaviour (1910, reissued 1960); Paul D. Hurd et al., Principal Sunflower Bees of North America with Emphasis on the Southwestern United States (1980). Martin Lindauer Paleontology and classification Evolution According to S.I. Malyshev, a Soviet entomologist, the first hymenopterans appeared early in the Mesozoic Era (about 225,000,000 years ago)about the same time as the first butterflies, moths, and flies. It is his thesis that the Hymenoptera derived from the so-called Eumecopteraancestors of the modern scorpion fly (order Mecoptera), the first insects to undergo complete metamorphosis. Another expert fixes the appearance of the first Hymenoptera in the middle of the Jurassic Period (150,000,000 years ago). So-called protohymenopterans, found in Permian beds (250,000,000 years old) in Kansas, have been regarded by some paleoentomologists as ancestral to the modern order. These resembled modern sawflies in having forewings and hindwings of about equal size and in lacking marginal hooklets for joining the two pairs. True sawflies (Tenthredinoidea) are also extant from the Jurassic Period. Because of the many longitudinal veins in the wings of these forms, they were believed to share a common origin with cockroaches, which have wings that exhibit a similar vein pattern. Many fossil ants are known from the Early Tertiary Period (60,000,000 years ago), both from Europe and North America. Some of them have been assigned to living genera. Males, females, and workers were already clearly differentiated in ants at that time. The aculeates, or stinging Hymenoptera, were one of the most recent large groups of insects to evolve. By the Tertiary Period both parasitic forms and aculeates had become abundant. The first bees, according to the fossil record, appeared in the Miocene Epoch (26,000,000 years ago). These were leaf-cutting bees (Lithargus). Since many of the flowering plants depend upon bees for pollination, it is believed that such plants and bees evolved at about the same time. Classification Annotated classification Some disagreement on the taxonomic structure of the order Hymenoptera exists among systematists. For many years it was customary to separate the suborder Apocrita into two subdivisions: the stinging forms (Aculeata) and the parasitic forms (Parasitica). So many exceptions to such a dichotomy were encountered, however, that it has been generally discredited. Biologically, the basis for such a separation is slim. Many forms assigned to the Parasitica are phytophagous, and a number of the Aculeata are parasites. In the generic, or nontaxonomic, sense the term aculeate still applies to the stinging forms. The classification given below is based on that of Borror and DeLong (1964), which, in turn, is essentially that of Muesebeck et al. (1951) and Krombein et al. (1958). It covers 71 families, of which 28 are relatively scarce.