Butterflies and Moths
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Butterflies and Moths
members of the order Lepidoptera, a large (more than 140,000 species) order of insects which undergo complete metamorphosis. Lepidoptera have two pairs of wings which are covered with scales. The mouth is a sucking one in the form of a proboscis; it is curled up when in a resting position. The body is densely covered with hairs and scales. The prothorax is poorly developed, with movable jointed processes called patagia. The mesothorax has movable plate-like processes, or tegu-lae. The abdomen has ten segments. In a majority of instances the female has separate copulative and ovipositor openings. The larvae, or caterpillars, have chewing mouth-parts. The pupae are usually of the obtect type, with extremities and wings which are closely fixed to the integument. The Lepidoptera differ in size. The largest is the South American owlet moth (Erebius [Thysania] agrippina) with a span of up to 30 cm. Among the European Lepidoptera, the largest is the giant silk moth, or Saturnia pyri (12–15 cm). There are also midget forms with wings about 3 mm across, for example, the pygmy moth (Stigmellidae).
The order was named from the scales (“pollen”) which cover their wings. These scales are modified and thickened hairs. The entire exceptional diversity of colors and patterns of the wings of Lepidoptera is created by the structure and pigmentation of their scales. The color generally is determined by varying kinds of pigments, but the brightest shining colors (iridescence, luster, and so forth) are caused by the very thin structure of the scale surface which causes the complex phenomena of refraction and diffraction. The placement of the varicolored scales on the wing is specific and forms complex patterns which are characteristic for each species and often for each taxonomic group. The colors and patterns of the wings have a dual biological significance. For the butterflies which are active in the daytime, this is a means for recognizing others of the same species. Here a role is also played by the “concealed” (for man) patterns which are caused by the varying reflection by different wing parts of ultraviolet rays which are perceived by the insect eye. The colors and patterns also play a protective role. The Lepidoptera show many remarkable examples of mimicry.
A majority of the Lepidoptera live a crepuscular or nocturnal way of life, and only the butterflies and skippers and a few representatives of other groups are active during the day. The Lepidoptera feed on the nectar of flowers, the juices of rotting fruit, and various sugary secretions of plants, but some of them (for example, the bagworms, lackey moths, and promi-nents) do not feed in an adult state, but live on reserve substances accumulated in fatty tissue during the larval (caterpillar) stage. The proboscis of Lepidoptera consists of a pair of greatly extended groove-like external lobes of the lower jaws fastened into the form of a tube through which food is sucked in. Of the remaining parts of a typical insect mouth, the Lepidoptera have only a pair of labial palpi which support the coiled proboscis on both sides. Often there are also maxillary palpi. In the nonfeeding species of Lepidoptera, the proboscis sometimes has completely disappeared. An excep tion among the Lepidoptera are the representatives of the family Micropterigidae which feed on the pollen of flowers and have kept the gnawing mouth parts with developed mandibles. This group serves as the connecting link between the modern higher forms of Lepidoptera and their extinct predecessors, which were close to the caddis flies.
The organs of vision in Lepidoptera are well developed. On the sides of the head are large hemispherical compound eyes consisting of an enormous number (up to 27,000) of om-matidia, which produce a general mosaic image. Above the compound eyes there often are two so-called simple eyes. Olfaction plays an important role in the life of Lepidoptera, particularly the nocturnal ones. The olfactory organs (the so-called sensillae) are located in large numbers on the surface of the antennae. The latter are extremely diverse, varying from setaceous to compound plumate antennae. In the males which seek out the immobile females -by smell (giant silk moths, tussock moths, and bagworms), the antennae are greatly branched and have a much larger surface than in the females. The organs of taste (the contact chemoreceptors) are located not only on the mouthparts but often on the legs. When the legs come into contact with a sugary liquid, a reflex causes the proboscis to uncoil. The presence of organs of hearing has been established as yet only in the higher forms of the order which are active at night. The auditory organs are located either in the area of the metathorax (owlet moths, prominents) or at the base of the abdomen (measuring worms and Pyralidae). The perceived sound waves lie in the high-frequency range (15–80 kilocycles per second). The Lepidoptera are also capable of perceiving the supersonic echo-location signals of bats, which makes it possible for the Lepidoptera to hide from them in time. To a significant degree the evolution of Lepidoptera has occurred in the direction of improving flight. This has been reflected in the structure of the wing and the thoracic area. In the primitive Lepidoptera (the suborder Jugatae) a similar form and a significant functional independence of the front and hind pairs of wings have been kept. In the suborder Frenatae, the fore pair of wings assumed greater and greater significance in flight, while the hind pair decreased in size and lost a portion of the veins. Accordingly, the mesothoracic segment and its musculature were progressively strengthened, while the metathoric segment was weakened. The subordination of the hind wings to the fore wings was aided by a coupling device in the form of bristles, located at the base of the hind wing, and catches on the lower surface of the fore wing. Nearly perfect flight is achieved in the hawkmoth, where high speed (up to 54 km/hr) is combined with great maneuverability, making it possible for it take nectar from flowers on the wing. In many Lepidoptera, long migrations of hundreds of kilometers have been noted, while the American butterfly Danaus plexippus makes regular seasonal migrations.
Lepidoptera are dioecious, and only rarely is natural parthenogenesis noted. In Lepidoptera the sexual dimorphism is sometimes sharply expressed. Aside from differences in the structure of the antennae, the males, as a rule, are smaller than the females and are often of a different color, for example, the gypsy moth, the brimstone butterfly, and the Euchloe cardamines. The strongest manifestation of dimorphism is the partial or complete loss of wings by the female (tussock moths, certain measuring worms, and particularly the bag-worms). In the bagworms, the females are often wormlike and are devoid not only of wings but even of legs and antennae. In many cases the winglessness of the females is related to climatic conditions and is particularly typical for the species of Lepidoptera which fly early in the spring or late in the autumn, as well as for alpine and arctic species.
Development. The development of Lepidoptera occurs with complete metamorphosis. The eggs are rich in yolk and are sheathed in a strong external membrane (chorion), the surface of which has a microsculpture which is specific for the species or group. The egg membrane has a complexly organized micropylar opening through which the sperm penetrates during fertilization. The shape of the eggs in the primitive groups is most often flattened-oval, and in the higher forms the eggs are hemispherical or bottle-shaped. As a rule, the eggs are laid separately or in groups on a plant which serves as the food for the caterpillar. In a majority of species, the number of eggs laid runs into the hundreds, reaching 2,000–3,000 for certain owlet moths. The caterpillar stage is morphologically rather uniform. Only the caterpillars of the Micropterygidae differ sharply, and in terms of a majority of features they are closer to the larvae of the order Mecoptera. In the remainder, the number of abdominal legs and the degree of hair development on the body are most variable. On the body there are always hairs (setae), even if the moth or butterfly is seemingly naked. These hairs fulfill the function of tactile receptors. In many species which live openly (in places where they can be influenced by the light, wind, and other external conditions), a dense secondary cover of hairs develops (the Arctiidae, Lasiocampidae, tussock moth, and others). Growth is accompanied by molts. Usually there are four molts and, correspondingly, five periods between molts. A predominant portion of the caterpillars is herbivorous. A covert way of life and feeding in rolled-up leaves, tissues of the leaf, fruits, stems, and roots are characteristic for the caterpillars of the more primitive groups of the order. In the evolutionarily younger families, most caterpillars lead an overt way of life and feed on leaves or coniferous needles. Along with the widely observed polyphagia (for example, in the turnip moth, the gypsy moth, and the beet webworm), the phenomenon of oligophagy is very widely found, that is, adaptation to feeding on a limited group of plants, usually taxonomically related and close in terms of biochemical composition. For example, the caterpillars of the large white (cabbage) butterfly and of many other Pieridae feed only on plants from the Cruciferae family which contain mustard glycosides. An example of extreme food specialization is the Chinese silkworm, which develops normally only if it feeds on the leaves of the white mulberry (Morus alba). The lower plants are used by only a few species (Lithosiinae and fungivorous moths). Even more rarely observed is the feeding on substances of animal origin such as wax (wax pyralid) and wool (the common clothes moth and the casebearing clothes moth). The only predators are the caterpillars of certain moths which feed on scale insects and scale.
The ability to secrete silk is characteristic of all caterpillars. The excretory duct of the silk-secreting glands opens on a special process of the labium, the spinneret. The silk is used by the caterpillars for fastening leaves, for building nests and shelters, but particularly for spinning a cocoon, or protective membrane, within which the caterpillar pupates. An overwhelming majority of the pupae of Lepidoptera are of the obtect type, where only certain abdominal segments remain mobile. Only in the families of Micropterygidae and Eriocraniidae are the cocoons of the exarate, or free type, and all parts of the body and extremities possess some mobility. As a lepidopteran emerges from the cocoon, its wings are still short and soft. Under the pressure of the hemolymph which is forced into the veins of the wing, they straighten out, increase in size by serveral times, and soon harden. After this the lepidopteran is ready for flight.
Fossil remains. Reliable fossil remains of Lepidoptera are known only from the Paleogene, predominantly from Baltic amber. All the species which have been found here already belong to the modern families and often to existing genera or genera that are very close to them. The development of the order has tentatively been placed in the Mesozoic (Jurassic). The Lepidoptera are undoubtedly one of the youngest orders of insects, and their development to a significant degree has paralleled the evolution of flowering plants.
Modern species. The varieties of Lepidoptera are richest in the tropics, where the largest forms are found. The largest forms often amaze one with the vividness and beauty of their color (for example, the South American genus Morpho, or the Indo-Malayan Ornithoptera). Toward the poles, the variety gradually decreases, but even beyond the arctic circle it is still rather abundant. Certain species such as the fritillary (Argynnis polaris) and the tussock moth (Dasychira rossii) reach as far as 82° N lat. The total number of Lepidoptera species found on Soviet territory exceeds 15,000. Of these, about two-thirds belong to five families: leaf rollers (Tortricidae), Gelechiidae, pyralids (Pyralidae), measuring worms (Geometridae), and owlet moths (Noctuidae).
Taxonomy. The order of Lepidoptera is divided into two suborders: Jugatae and Frenatae. In the Jugatae the fore and hind wings are almost equal in size and shape. The radial vein always has four to five branches. The wings are held together by a special lobe (jugum) on the fore wing. This suborder includes the most archaic families such as Micropterygidae, Eriocraniidae, and the ghost moths (Hepialidae).
In the suborder Frenatae, the fore and hind wings are of different shape. On the hind wings the radial vein is devoid of branches, and the wings are held together by a catch, or frenulum. The suborder Frenatae includes the predominant portion of all Lepidoptera. There are more than 70 families forming two large groups: Microfrenatae and Macrofrenatae. The Microfrenatae include the more primitive and predominantly the small Lepidoptera. The basic families are the pygmy moths (Stigmellidae), the clothes moths (Tineidae), the bagworms (Psychidae), Anthroceridae, the clearwings (Aegeriidae), the goat moths (Cossidae), the leaf rollers (Tortricidae), Lithocolletidae, the ermine moths (Ypono-meutidae), Gelechiidae, Pyralidae, and Pterophoridae.
The group Macrofrenatae includes the highly organized, comparatively large butterflies. The series of families of Rhopalocera includes the generally known diurnal butterflies such as the skippers (Hesperiidae), the swallowtails (Papilionidae), the white cabbage butterflies (Pieridae), the blue butterflies (Lycaenidae), and Nymphalidae.
Among the nocturnal Lepidoptera, or moths (Heterocera), are the following basic families: the tent caterpillars and lappet caterpillars (Lasiocampidae), Bombycidae, Attacidae, the hawk moths (Sphingidae), the measuring worms (Geometridae), the prominents (Notodontidae), the tussock moths (Lymantriidae), Arctiidae, Syntomididae, and the owlet moths (Noctuidae).
Economic significance. The herbivorous nature and the enormous number of species determine the great role of Lepidoptera in nature and in the economic activity of man. On Soviet territory, about 1,000 species of Lepidoptera feed on cultivated plants, among which are such important pests as the cutworm, the cotton bollworm, the cabbage moth, and other noctuids, the beet webworm and European corn borer, the codling moth, the Oriental fruit moth, and the plum fruit moth. Equally numerous are the tree pests which cause enormous harm to forestry. Thus, breeding outbursts of the Siberian silkworm moth (Dendrolimus sibiricus) can lead to the desiccation of coniferous forests on areas of hundreds of thousands of hectares. A number of species of Lepidoptera, predominantly of the Pyralidae and Tineidae which have adapted themselves to living in houses and warehouses, damage food supplies, fur, and woolen and silk articles.
The useful activity of Lepidoptera in nature is related to their participation in pollinating flowering plants, particularly nocturnal ones. Certain species of Lepidoptera are raised for producing silk. The domesticated Chinese silkworm, which originates in Southeast Asia, is the basic producer of natural silk. A coarser silk, of the tussah type, is produced by certain semi wild Asian giant silk moths, for example, the Chinese oak silkworm and the ailanthus silkworm.
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