GRASSHOPPER

Learning Objectives
After reading this, you should be able to:
1) Differentiate between the nymph and adult of grasshopper

2) Outline the mode of l fe of grasshoppers.

3) Explain the economic importance of grasshoppers.
Grasshopper [ Valangra nigricornis ]


CRASSHOPPER: Valangra nlgricornls

Grasshopper is a common name for a group of insects that belong to the order Orthoptera (Le. straight wings). There are over 10,000 speCies of grasshoppers worldwide, with a predominantly tropical distribution. Depending on the length of the antennae, grasshoppers may be grouped as short-horned or longhorned. When some short-horned grasshoppers reproduce too rapidly for their f00d supply to support them, subsequent generations undergo extensive changes in form and become migratory. Such short horned grasshoppers are known as locusts and make up the family, Acrididae.


The External Structure (Zonocerus variagatus & Valangra nigricomis)
The body of the grasshopper comprises: head, thorax and abdomen. The head bears a pair of antennae which is sensitive to smell, touch and vision. Also on the head are two sets of eyes which include three simple eyes and a pair of very large compound eyes. The location of the eyes is neither forwards nor side ways. The compound eyes are made up of several six sided lenses which enable the organism to view all directions at the same time. Focusing of the eyes is not sharp.

The lower part of the head bears the mouthparts, which consists of labrum, The External Structure (Zonocerus variagatus & Valangra nigricomis)

The body of the grasshopper comprises: head, thorax and abdomen. The head bears a pair of antennae which is sensitive to smell, touch and vision. Also on the head are two sets of eyes which include three simple eyes and a pair of very large compound eyes. The location of the eyes is neither forwards nor side ways. The compound eyes are made up of several six sided lenses which enable the organism to view all directions at the same time. Focusing of the eyes is not sharp.

The lower part of the head bears the mouthparts, which consists of labrum, labium, mandibles, maxillae and labium. They help the insect to handle and chew food. The‘mandibles form the ventral jaw which serves to cut up and crush food particles. They work side by side. The maxillae flank the mandibles. The inner part of each maxilla directs food to the mandibles. It also cut and grinds food. The outer part of the maxillae is modified to maxillary palps which has a sensory function. The labium is the lower lip of the mouth. It bears sensory palps called labial palps. Labrum forms the upper lip of the mouthparts. It has a small notch which helps to hold leaf in place. The grasshopper also has epipharynx and hypo pharynx. The epipharynx fuses with the inner surface of the labrum and continues with the roof of the mouth. In other insects, the epipharynx forms the proboscis (sucking mouthpart). The hypopharynx are small tongue-like structures which are attached to the labium. It bears the Opening of salivary glands.


The thorax is divided into three parts: prothorax, me'sothorax and metathorax. The last two bear a pair of wings each. There are three pairs of legs, one on each thoracic segment. The third pair of legs is very large and is used for jumping in order to escape from enemies, search for food and in preparation for flight The walking legs are used for climbing. Each foot possesses pads and spines which aid the organism to grip surfaces firmly. The two pairs of wings are known as fore and hind wings. The fore wings, called tegmina, are stiff and narrow. The hind wings are broad, transparent and membranous and are used for flight whilst the fore wings are used to protect the hind wings. Both wings fold over the abdomen when the grasshopper is not flying. On jumping, the partially folded hind legs are fully extended and thus pushing the insects upwards and forwards. The wings may be reduced or absent. Females have much shorter wings than males. The grasshopper flies only for short distances and lands on its fore and middle legs.

The abdomen bears ten segments and each segment has two plates: upper and lower plates or sclerites. These are joined by tough but flexible membranes which permit movement of the appendages: legs, wings, antennae. The first to eighth abdominal segments have a pair of spiracles each, which lead to the tracheal system to form complex network. Portions of the tracheal system in the abdomen form thin walled structures called air-sacs, which help the insect to increase the volume of air space and reduce their body density.

The last abdominal segment bears cerci (singular: circus), which are sensory in function. The segment also bears lobes called paraprots. Claspers and aedeagus are the sex organs and they are borne on the ninth segment. The clasper is used for holding the female while the aedegus is used for introducing sperms into the female body. The last sterna of the female are modified into a structure called ovipositor. This enables the grasshopper to dig a hole in the ground and lay eggs into it.



Mode of Life
Grasshoppers can be found in every part of the world. They are diurnal insects and therefore very active during the day and are seen in gardens, farmlands and open grasslands. They are therefore terrestrial organisms. They feed on varieties of foods including blade of grasses and vegetations. On jumping, the partially folded hind legs are fully extended and thus pushing the insects upwards and forwards. The grasshopper flies only for short distances and lands on its fore and middle legs. The pair of hind legs is very large and is used for jumping; in order to escape from enemies, search for food and in preparation for flight. The walking legs are used for climbing. Each foot possesses pads and spines which and the organism to grip surfaces firmly. The pair of compound eyes and the three simple eyes are used for vision. The pair of antennae on the head is sensitive to smell, touch and vision. The grasshopper breathes by means of spiracles which are connected to tracheal system. The membranous exoskeleton protects the organism from desiccation and mechanical injuries.


Adult male grasshoppers chirp usually by rubbing the inner side of the hind legs against veins on the forewings. The recognizable "songs" they produce are distinctive for each species and are used in courtship. Some females also produce sounds. Theirhearing organs are on the abdomen, just behind the junction of the hind legs with the body. The female digs a hole in the ground and lays the fertilized eggs in it. Some species show arrested development of eggs, called diapause, during adverse climatic conditions. In temperate zones, there is usually an annual life cycle, but in tropical areas, breeding may be continuous with several generations each year. The grasshopper undergoes incomplete metamorphosis. The colour of the grasshopper is used for camouflaging, which helps it to escape enemies and predators.


Fertilization in grasshopper is internal. The female has seminal receptacle in which sperms received during mating are stored. The stored sperms only fertilize the eggs when they are matured. The posterior portion of the
female bears a hard pointed organ called ovipositor. which is used to dig a hole in the ground in which the fertilized eggs are laid. The female secretes gum which covers the eggs as protective devices. With the presence of enough warmth and moisture the eggs hatch in two to three days into nymphs which moult five times to become adults. The grasshopper, therefore, undergoes incomplete metamorphosis.


The External Structures of the Nymph
       The nymph is light brown in colour and about six millimetres long. They have no wings but resemble the adults in all other respects. They feed and moult until they increase in size to reach adult size or stage. The nymph takes about thirty to fifty days to become adult. The period between two moultings is called instars. The internal organs develop fully by the time of the last moulting.


Structural Differences between Adult Grasshopper and Nymph
     Though the young grasshoppers (nymphs) are miniature versions of the adult, they lack wings but the adults have wings. Cerci are absent in the nymphs but present in the adults.

Economic Importance
Grasshoppers have powerful mouthparts suitable for biting and chewin and are herbivorous. They feed on a wide range of plants, including important crops, the most serious damage being inflicted by locusts. Some people feed on them.

As such, they cause extensive damage to valuable crops and garden plants. They destroy leaves including tender portions. They thus, feed on the whole herbaceous plants. This causes famine resulting in starvation and death.


Control Measures
     The most effective control measures include aerial spraying using helicopters and low flying aeroplanes. Devices such as radar, computers and satellites can be used to detect the movement and concentrations of the swarms. Insecticides such as carloamate bendiocarbs, fenitrothin and synthetic pyrethroids can be used to spray the swarms of grasshoppers or locusts. These chemicals kill the target insects (locusts) and exclude non-targeted ones. Predators such as lizards may be used to control grasshoppers.






I Hope You Now Know More About A Grasshopper.

NOW Answer The   Questions Below

1. Briefly outline the life cycle of a grasshopper.

2. How is the grasshopper adapted to its environment?

3. Outline the economic importance of the grasshopper to humans.

4. Explain how you would control grasshoppers on a maize farm.





       ACTIVITY

         Observing A Grasshopper

1. Collect specimens of nymph and adult grasshopper.

2. Examine the specimens carefully with a hand lens.

3. Draw and label lateral viewsof the nymph and adult grasshopper.

4. Why is the size of the two pairs of front legs so different from that of the hind legs?

5. What are the main differences in the external features of the adult and the nymph?

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