- Related Topics:
- ice bug
- phasmid
- Orthoptera
- Dictyoptera
- Exopterygota
Some orthopterans make conspicuous sounds, while others produce sounds that are outside the range of human hearing. In both cases sound production is important to behavior necessary for success of the species concerned. All major groups of orthopterans produce some sort of sound, though sound production is widespread only in crickets, katydids, and grasshoppers.
The stridulatory mechanism of grasshoppers involves moving the hindleg across the folded front wing (tegmen). Serrations, or pegs, which vary in shape, number, and location among different species, are located on the inner surface of the femur and rub across special raised veins of the tegmen, creating a characteristic lisp; sometimes the serrations are on the tegminal veins. In the hindwings of other grasshoppers are stiff veins that make a crackling sound (crepitation) in flight.
Among male crickets and katydids, a front wing with an enlarged transverse vein near its base bears teeth that rasp when shuffled across a scraper on the other front wing. The row of teeth is called the file, and the membrane to which it is attached vibrates when the teeth move over the scraper. During stridulation the tegmina are lifted at an angle of 15° to 40° to the surface of the abdomen, then rapidly opened and closed (shuffled); sound is produced during the closure.
The best-known auditory organs of orthopterans, the tympanic organs on each side of the abdomen, are found in both sexes of grasshoppers and on the front tibiae of most crickets and katydids. There are auditory nerves running from special cells beneath a tympanic membrane (a thin area of cuticle, backed by an air sac and free to vibrate) to a ganglion of the central nervous system. In addition to these evident tympanic structures, other less evident auditory organs occur in the orthopterans. Many orthopterans, however, have no conspicuous tympana and are entirely dependent for sound reception on sensory hairs located on cerci, the head, other parts of the body, and an auditory organ called Johnston’s organ, which is widespread in the second segment of the antenna.
Evolution and paleontology
Ensifera occur from the Triassic to the present; apparently Ensifera and Caelifera separated as distinct evolutionary lines as early as the Carboniferous. The earliest fossils in the acrididoid line had long antennae. Shorter antennae, reduction of tarsal segments to three, and reduction in length of the ovipositor occurred by the Eocene Epoch (56 million to 34 million years ago).
By the late 19th century, all principal groups of orthopterans were represented in collections; however, the order Orthoptera, broader in scope than it is at the present time, included earwigs, cockroaches, mantises, walking sticks` and other groups. By the 20th century, however, basic morphological studies, as well as extensive reports on fossils, contributed new insights into the fundamental relationships of the major groups. In the late 1930s extensive studies of fossils were correlated with important work on current species, especially concerning the Orthoptera (restricted sense). Meanwhile, comparative studies of wing venation, the proventriculus, reproductive organs, and behaviour have steadily advanced the knowledge of group relationships. Additional details and supporting data, for example, were given in an extensive phylogenetic study in 1968. The rank of a suborder (Acridomorpha) for grasshoppers alone (Eumastacoidea through Acridoidea of this article) has not been evaluated sufficiently. Many of the earliest fossil orthopterans were different enough from any present ones to justify the recognition of separate though extinct families.
Classification
Distinguishing taxonomic features
Among the distinctive features of orthopterans are their wings, which, when present, usually number four. The two forewings, generally long and narrow, are many-veined and somewhat thickened. ++-he forewings, hardened and of a leathery consistency, are known as tegmina. The hindwings, broad with many veins, usually are folded fanlike beneath the forewings when at rest. The females have ovipositors. Some are concealed by ventral abdominal segments; others are as long as the body. Orthopterans have mandibulate mouthparts adapted for chewing and undergo simple metamorphosis.
The classification of orthopterans into orders and families is based chiefly on comparative morphology, on indications of ancestry derived from fossils, and on relationships suggested by patterns of behavior and the physiology of body systems. Similar anatomical structures that have been significant in deducing orthopteran relationships include: tarsal segments; hindlegs; wings; stridulatory and auditory organs; head capsule; thoracic sclerites; ovipositor; male genitalia; and proventriculus. In recent years correlations between behavior and mating and reproduction, especially in cockroaches and crickets, have been used widely to support classification of families and subfamilies as well as distinctions between species.
The cerci lack segments are lacking in katydids, crickets, and grasshoppers. The external male genitalia are sometimes concealed and symmetrical. The Orthoptera have the femur of the hindleg enlarged for jumping; other groups have hindlegs similar in size to the middle legs. In mantids the front legs are modified for seizing prey, in mole crickets for digging. The tarsus consists of three or four segments. The antennal segments vary from fewer than seven to many long and setaceous ones.