The Grasshopper

In this section, the grasshopper will be used to demonstrate some of the details of insect structure and function. As you read, remember that these details are not shared by all insects. The diversity of the insect world is so great that no typical insect exists.

External Structure

The major features of an adult grasshopper's external structure are illustrated in Figure 37-3. The body of a grasshopper clearly shows three tagmata. The most anterior tagma, the head, bears the mouthparts. It also has a pair of unbranched antennae as well as simple and compound eyes.

The middle tagma, the thorax, is divided into three parts: the prothorax, mesothorax, and metathorax. The prothorax attaches to the head and bears the first pair of walking legs. The mesothorax bears the forewings and the second pair of walking legs. The metathorax attaches to the abdomen and bears the hindwings and the large jumping legs. The muscles inside the jumping legs store energy when the legs are flexed. Release of this energy causes the legs to extend suddenly, launching the grasshopper into the air and away from danger. A flexible joint at the base of each leg provides the legs with great freedom of motion. Spines and hooks on the legs enable the grasshopper to cling to branches and blades of grass.

The leathery forewings cover and protect the membranous hindwings when the grasshopper isn't flying. Although the forewings help the grasshopper glide during flight, the hindwings actually propel it through the air. The wings are powered by muscles attached to the inside of the exoskeleton in the thorax. Note that insect wings develop as outgrowths of the thorax and are composed of exoskeleton material. Thus, they are not homologous to bird and bat wings, which develop from limb buds.

The segments in the most posterior tagma, the abdomen, are composed of upper and lower plates that are joined by a tough but flexible sheet of exoskeleton. The same flexible sheet also connects the segments to one another. The exoskeleton is covered by a waxy cuticle that is secreted by the cells of the epidermis. The rigid exoskeleton supports the grasshopper's body, and the cuticle retards the loss of body water. Both structures are adaptations for a terrestrial life.

www.scilinks.org Topic: Grasshoppers Keyword: HM60688

www.scilinks.org Topic: Grasshoppers Keyword: HM60688

Maintained by the h j National Science I. \ J\ .3. Teachers Association

Maintained by the h j National Science I. \ J\ .3. Teachers Association figure 37-3

The external anatomy of a grasshopper shows features that are characteristic of most insects: a body consisting of a head, thorax, and abdomen; a pair of unbranched antennae; three pairs of jointed legs; and two pairs of wings.

Where Grasshopper TympanumMouth Part Grasshopper
(a) GRASSHOPPER MOUTHPARTS
Mouth Part Housefly
(b) MOSQUITO MOUTHPARTS
Mouthpart Housefly

(c) HOUSEFLY MOUTHPARTS

figure 37-4

Insect mouthparts are adapted for different functions in different species. Mouthparts are used for biting and chewing in grasshoppers (a), piercing and sucking in mosquitoes (b), and sponging and lapping in houseflies (c).

(c) HOUSEFLY MOUTHPARTS

figure 37-4

Insect mouthparts are adapted for different functions in different species. Mouthparts are used for biting and chewing in grasshoppers (a), piercing and sucking in mosquitoes (b), and sponging and lapping in houseflies (c).

Feeding and Digestion

Grasshoppers feed on plants. The mouthparts of grasshoppers, shown in Figure 37-4a, are modified for cutting and chewing leaves and blades of grass. The labrum and labium are mouthparts that function like upper and lower lips, respectively. They hold the food in position so that the sharp-edged mandibles can tear off edible bits. Behind the mandibles are the maxillae, which also help hold and cut the food. Recall that all anthropods have mandibles and maxillae.

The mouthparts of other insects are specialized for the types of food they eat, as you can see in Figures 37-4b and 37-4c. For example, mosquitoes have long, thin mouthparts that fit together to form a needle-like tube, which the females use to pierce the skin of other animals and suck up blood. The mouthparts of many flies, in contrast, are soft, spongelike lobes that soak up fruit juices and other liquids.

The digestive tract of a grasshopper is shown in Figure 37-5. Food enters the mouth, is moistened by saliva from the salivary (SAL-uh-VER-ee) glands and then passes through the esophagus and into the crop for temporary storage. From the crop, food passes into the gizzard, where sharp, chitinous plates shred it. The shredded mass then enters a portion of the digestive tract called the midgut. There, the food is broken down by enzymes secreted by the gastric ceca (GAS-trik SEE-kuh), which are pockets that branch from the digestive tract. Nutrients are absorbed into the coelom through the midgut. Undigested matter enters the posterior section of the digestive tract, the hindgut, and leaves the body through the anus.

Circulation, Respiration, and Excretion

Nutrients and other materials are transported through the body of a grasshopper by an open circulatory system that is similar to that of the crayfish. Hemolymph flows through a large dorsal vessel called the aorta (ay-OHR-tuh), which is shown in Figure 37-5. The muscular heart, which is located in the abdomen and thorax, pumps the hemolymph forward through the aorta and into the part of the coelom nearest the head. The hemolymph then percolates through the coelom toward the abdomen and reenters the heart through small pores along its length.

Most animals transport oxygen and carbon dioxide through their circulatory system. However, insects exchange these gases with the environment through a complex network of air tubes called trachea. Trachea also serve this purpose in some spiders. In grasshoppers, air enters the tracheae through spiracles on the sides of the thorax and abdomen, as seen in Figures 37-3 and 37-5. The ends of the tracheae branch near the cells of the body and are filled with fluid. Oxygen diffuses into the cells from this fluid while carbon dioxide diffuses in the reverse direction. Air can be pumped in and out of the tracheae by the movements of the abdomen and wings.

Grasshopper Tracheal Tubules

figure 37-5

The major internal organs of a female grasshopper are seen in this cutaway side view.

Like spiders, insects have excretory organs called Malpighian tubules that collect water and cellular wastes from the hemolymph. As Figure 37-5 shows, the Malpighian tubules are attached to the digestive tract between the midgut and the hindgut. In insects that live in dry environments, the Malpighian tubules return most of the water to the hemolymph, producing a very concentrated mixture of wastes that is deposited in the hindgut and leaves the body with the feces. This is another method by which insects are adapted for life on land.

Neural Control

The grasshopper's central nervous system consists of a brain and a ventral nerve cord with ganglia located in each body segment. Nerves extend from the brain to the antennae, eyes, and other organs of the head. The antennae contain sensory structures that respond to touch and smell. The three simple eyes are arranged in a row just above the base of the antennae. The simple eyes function to sense the intensity of light. Two bulging compound eyes, which are composed of hundreds of individual light detectors and lenses, provide a wide field of view. In addition to sensing light intensity, the compound eyes can detect movement and form images.

Other nerves extend from the ganglia to the muscles and sensory structures in the thorax and abdomen. One such structure is a sound-sensing organ called the tympanum (TIM-puh-nuhm). The tympanum is a large, oval membrane that covers an air-filled cavity on each side of the first abdominal segment. Sounds cause the tympanum to vibrate, and the vibrations are detected by nerve cells that line the cavity. Tympana are also found in many other insects that use sound in communication, such as crickets and cicadas. In addition, sensory hairs that are similar to those of a crayfish are distributed over an insect's body. At the base of each hair is a nerve cell that is activated if the hair is touched or moved by vibration.

figure 37-5

The major internal organs of a female grasshopper are seen in this cutaway side view.

Word Roots and Origins tympanum from the Latin tympanum, meaning "drum"

Word Roots and Origins ovipositor from the Latin ovum, meaning "egg," and positus, meaning "to place"

Reproduction

Grasshoppers have separate sexes, as do all insects. During mating, the male deposits sperm into the female's seminal receptacle, where they are stored until the eggs are released by the ovaries. After release, the eggs are fertilized internally. The last segment of the female's abdomen forms a pointed organ called an ovipositor (OH-vuh-PAHZ-uht-uhr), which you can see in Figure 37-3. The female grasshopper uses her ovipositor to dig a hole in the soil, where she lays the fertilized eggs.

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  • KAARINA
    Where the tympanum be found in grasshopper?
    1 year ago

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