Harmful Animal

The harmful animals are those that cause injury to plants and domes­tic animals. Human beings are affected directly or through bites or stings or by transmission of various kinds of pathogens. The nature of harmful insects ranges from simple nuisance value of cockroaches to spreading of epidemic diseases, such as malaria, filariasis by mosquitos. For the convenience of our study the harmful animals are grouped under the following categories namely disease causing organisms, poisonous animals, fouling organisms and pests.

1-1 Disease causing organisms - Vectors

Some insects are injurious to man as vectors of human diseases. Through the ages millions of people have died of diseases transmitted by insects. There are a number of insect-borne diseases, and they may be transmitted in different ways.

Fig.1. Insect - Vectors

1-Housefly - Musca domestica

House flies are cosmopolitan in distribution. They are closely associated with humans and thrive best where people are careless in the disposal of wastes. Adult flies are nonparasitic.

They feed on all kinds of decaying and decomposing matter. It is an important mechanical vector in the transmission of diseases like typhoid (Salmonella typhosa - a bacterium), dysentery (Entamoeba histolytica) and cholera (Vibrio sps.) The housefly causes diseases through food contaminations.

Control: Housefly control is normally done in 3 different ways, namely sanitary, mechanical and chemical methods. Populations of houseflies can be controlled by proper disposal of manure, garbage, sewage, food waste, human excreta and other organic materials. Mechanical practices such as screening, using of traps or sticky paper or baits can be valuable in excluding houseflies. Insecticides may be used against larvae. Spraying with 2% malathion 1% chlordane or lindane, 0.5% tremephos are effective.

2-Sand flies - Phlebotomus papatasi

These flies are 4 mm long. Only the female possess piercing-sucking mouth parts and are haematophagous. The males are non-parasitic, feeding on moisture. They are small slender insects with hairy bodies. Through biting this fly transmits the disease called kala-azar. The causative organisms are Leish- mania, a parasitic protozoan. During the day time the flies remain hiding. At night they come out to feed. The sand fly attacks during night times. The insect sucks the parasite from an infected person, along with blood. Inside the body of the fly, the parasite undergoes changes. When an infected fly bites man, the parasites pass into the blood and fresh infection is effected. The parasites mostly concentrate in the capillaries of spleen, liver and bone marrow. The disease is characterized by the symptoms like anaemia and emaciation

Control:

Spraying of 5 % DDT / BHC easily kills the flies. The pyrethrum ointment used on exposed part of the body works as a repellent.

3-Rat fleas - Xenopsylla cheopis

The insect parasite, Xenopsylla cheopis is commonly known as the Asiatic rat flea. Both male and female fleas take in the bacillus pasteurella pestis from infected rats during feeding. This rat - flea is responsible for the transmission of plague from man to man, or from rat to man. When this bacterium is introduced into the skin, the lymph glands become inflamed. This is known as bubonic plague. Frequently, the bacilli become established in the victim's blood. The condition is then referred to as septicemia plague. If the victim’s lungs become involved, it is referred to as pneumonic Plague

When the rat flea sucks the blood of man or a rat infected with plague, the bacilli enter into its stomach and grow there into large numbers. The flea thus heavily laden with the bacilli may bite a healthy man and introduce the bacilli into the wound and cause infection. The bacilli are deposited by the flea on the skin along with the faeces. The bite of the flea causes scratchings and the bacilli are introduced into the blood when the skin is scratched.

Control:

Destruction of rats and other rodents is an effective method. Dusting of 1 to 2 % chloradane, or 2 % Y - BHC is very much effective in the elimination of fleas on the body of pet animals. Application of 5% DDT is recommended for spraying at the time of the spread of plague in all the areas.

4-The human louse - Pediculus humanus

Louse is a blood sucking ectoparasite of man. It is cosmopolitan in distribution.

The human louse is a major vector for three important human dis-eases, relapsing fever, typhus and trench fever.

Disease                   -                      Parasite

Relapsing fever      -                      Borrelia  sp

Typhus                   -                      Rickettsia sp

Trench fever          -                      Rickettsia sp

Control: Wearing clean clothes, and having regular bath avoids infestation.

5-Mosquitoes: Anopheles, Culex, Aedes sp

Mosquitoes are cosmopolitan in distribution. They are nocturnal in habit and are found in abundance in damp, marshy lands near stagnant water. Only female mosquitoes are adapted to suck the blood of human beings and function as carrier of viral, protozoan and nematode diseases.

Culex mosquitoes serve as the vectors for filariasis or elephantiasis. This disease is caused by the nematode parasite, Wuchereria bancrofti. It is commonly known as filarial worm. It is found in the lymphatic vessels and lymph glands of man. The female worms give birth to living embryos known as microfilariae. The microfilariae normally circulate at night (10 to 2 am) in the peripheral blood. At that time they are ingested by the mosquito along with blood, the mosquito is not just a mechanical carrier of the parasite. Developmental changes take place in the body of the parasite. When the infected mosquito next bites another person, the larvae penetrate the superficial skin to find their way into the lymphatic vessels, and attain sexual maturity. In severe infection the adults cause blocking of lymphatic system which results in the enlargement of legs, arms, scrotum, and mammary glands. It is known as elephantiasis.

The Anopheles mosquito transmits plasmodium, a causative protozoan for malaria (Refer: Plasmodium)

Another type of mosquito, Aedes transmits yellow fever through a

Virus.

1-2 Poisonous Organisms

Fig.2. Poisonous animals

Free living organisms have developed some device to protect

themselves against predators. These protective devices ranges from the simple stinging cells of Physalia to the massive poison glands of the snakes. The list of poisonous organisms is exhaustive. A few of the important poisonous organisms are mentioned here.

Physalia

These are marine coelenterates. They are notorious for the painful sting they can inflict on unsuspecting swimmers who accidently brush against them. They attack using stinging cells on their trailing tentacles. Their powerful stings cause painful local inflammation and can even be fatal.

Scorpion.

In scorpion the sting is attached to the posterior part of the last segment. It consists of bulbous base and a sharp curved barb that injects the venom. The venom is produced by a pair of oval glands. The scorpion raises the posterior abdomen over the body making it curved forward. A stabbing motion is used in stinging.

The venom of most scorpions is sufficiently toxic to kill a vertebrate. The venom of the scorpion Androctonus is equivalent in toxicity to cobra venom.

The neurotoxic venom of scorpions is very painful and may cause paralysis of the respiratory muscles or cardiac failure in fatal cases. Anti-venoms are available for these species.

Centipede:

Centipedes are distributed throughout the world. They live in soil and humus and beneath stones. The largest centipede is the tropical American Scolopendra gigantea which may reach 26 cm in length. They have a large pair of poison claws sometimes called maxillipeds. Each claw bears a terminal pointed fang. The venom although painful is not sufficiently toxic to be lethal to man even to small children. However S. gigantea has been known to cause human death.

Honey bees and Wasps:

Fig.3. Poisonous insects

In worker honey bee (undeveloped females) the poisonous sting is situated at the hind end of the body. It is a pointed structure provided with minute hooks or barbs at its free end. On stinging the tip of sting gets detached. Hence a bee can sting only once.

Unlike the bee the wasp is able to withdraw its sting from the wound. Hence it can sting again. In wasp the sting is a modified ovipositor and once it has penetrated the skin of the victim poison is injected as in a hypodermic syringe. The wasp’s poison is histamine.

The sting by honey bees and wasps lead to pain and inflammation.

Poisonous fishes

More than 700 species of fishes have poison glands. Venom in fishes is of two kinds. One kind of venom is produced by specialized glands which may occur in various parts of the body. In the second, the flesh itself may secrete some toxic substance and the fish becomes poisonous and inedible.

There are several poisonous cartilaginous fishes. The poison glands are usually associated with a spine or sting as in the case of sting ray. In the sting ray(Trygon), the poison glands lie along a lateral groove on each side of the spine on its tail. The spine causes pain and numbness in the flesh of victim.

The large Barracuda of Cuba and other tropical islands have poisonous flesh, which when eaten cause pain in joints and extremities, nausea, vomiting and general trembling.

Fig.4. Poisonous fishes

The Puffer fish, (Tetrodon) is considered to be world’s most dangerous fish. Its ovaries, intestine, kidneys, skin and eyes contain a neurotoxin called Tetradoxin. This toxin has no antidote. It is several times deadlier than cyanide. In a dilute form, Tetradoxin is used as a pain killer for victims of neuralgia, arthritis and rheumatism

Fig. 5. Poisonous snakes

Indian poisonous snakes are the cobras, the kraits, the vipers and the sea snakes. These can be distinguished from the non-poisonous by the tail, the arrangement and size of scales, plates and shields found over the body.

Cobra: It is well known all over India. When provoked it raises its head and expand the skin of the neck region in the form of a characteristic hood. The hood may bear a spectacle mark. Such cobras are called two ringed or spectacled forms. In others there is a oval spot surrounded by an ellipse. These are known as the one ringed or monocled variety. They are found in Bengal. In still others there is no mark on the hood. Only two species of cobra are found in India. They are Naja naja (Indian cobra) and Ophiophagus hannah (king cobra).

Krait: These are common poisonous snakes of India. There are two com­mon Indian kraits. They are the common krait (Bungarus coeruleus) and the banded krait (B. fasciatus).

Vipers : There are two classes of vipers. Some have a distinct pit on the sides of the head between the nostril and the eye in the region called ‘lore’. These are called pit vipers. The other one is the pitless viper .Vipers is vivipa­rous in nature.

The vipers have movable upper jaw, so that the fangs when not in use can be folded backwards. It gets erected with the opening of the mouth while inflict­ing injury. It produces a loud hissing sound by expelling air through nostrils.

Pitless Viper - Vipera russellir (Russell’s viper) Echis carinata (The little Indian viper).

Pit viper - Trimeresurus sp

Sea Snakes: Sea snakes can always be distinguished from other snakes by their laterally compressed tails. This is an adaptation to their life in the sea. All sea snakes are highly poisonous.

Eg. Hydrophis sp Enhydrina sp

Poison Apparatus of a Snake

The poisonous snake possesses a poison apparatus comprising of a pair of poison glands, a pair of poison ducts and a pair of fangs. The poison glands are situated on either side of the upper jaw below and behind eyes. They are specialized salivary glands. A duct carries the venom secreted from each gland to the fang. A fang is meant for injecting the venom into the body of the prey. Fangs are specialized teeth of the upper jaw which are tubular or grooved.

Fig. 6. Snake jaw showing fangs and poison glands

Fig. 7. Fangs of snakes and marks left by the bite of poisonous and non-poisonous snakes

Biting mechanism in Cobra

Cobra is not an aggressive snake. When disturbed, it attempts to escape. When the snake attacks, the mouth opens by lowering the lower jaw. This makes the fangs to be erect to penetrate the muscles of the victim. When the mouth is closed the poison glands are pressed. The venom thus reaches the fangs and is injected into the body of the victim. This whole process takes place in no time.

Snake Venom

There are two types of snake venoms. One type acts mainly on the nervous system (neurotoxic). It affects the optic nerves (causing blindness) or the phrenic nerve of the diaphragm (causing paralysis of respiration). The other type is haemolytic. It breaks down the red blood corpuscles and blood vessels and produces extensive extravasation of blood into the tissue spaces.

1-3 Fouling Organisms

Several aquatic organisms cause damages to submerged surfaces. Since this infestation has an economical importance, several studies are being made. Marine sedentary organisms may affect piles, floats, wooden dry docks and boats. These organisms are called foulers. Most of these organisms are distributed all over the world through the agency of ships.

They are of economic importance, since fouling of ships results in increased resistance to movement through water, reducing the efficiency, lowering of speed, increasing fuel consumption and leading to wear and tear of engine. The efficiency of underwater sound equipment fitted on to commercial and naval vessels is also seriously affected as result of the accumulation of fouling organisms.

Pipes and conduits used to convey salt water in ships, industrial plants. oil refineries, nuclear power plants and aquaria become clogged and the flow is interrupted by the growth of these organisms inside the pipe. Thus the problem of fouling organism is serious.

Factors influencing the settlement of fouling organisms

Several factors are known to influence the settlement of larvae of fouling organisms. The most important of which is recognized to be the formation of the primary film. It is composed chiefly of diatoms and algal spores with a relatively small portion of bacteria. The thin filaments of algae may afford foothold on the substratum for the larvae to settle. The algae and diatoms serve as food for these larvae.

Members of the fouling community

The most important members of the fouling community include algae and representatives from almost all the invertebrate groups and the tunicata. Among the molluscs the mussels are the most important foulers. They settle heavily, especially in the pipe systems carrying seawater and obstruct the flow of water. Among Arthropoda, the barnacles are the dominant representatives of the fouling community. There are over 100 species of barnacles as foulers.

Fig. 8. Common foulers

1-Using copper sheathing on wooden hulls of boats

2-Applying suitable antifouling paint

3-Chlorination in condenser system

1-4 Pests

Any animal which becomes a source of trouble or loss to human is called a pest. Among insects such pests are numerous and are of different kinds. An insect is usually called as a pest when it causes appreciable damage and loss to the crops or other belongings. The pests may be classified as major or occasional. The insects damaging standing crops cereals, fruits and other plant products of commercial importance are designated as crop pests. Those insects destroying stored grains are called the store pest. Insects causing damage to household articles are called the household pests.

Pests of Crops

Fig. 9. Common pests of crops

I. Pest of Cotton

a. Pink boll worm - Pectinophora gossypiella

This pest causes damage to the buds, flowers and seeds.

b. Red cotton bug - Dysdercus koenigii

This bug sucks the cell sap of green bolls and leaves.

c. Spotted boll worm - Earias vitella, E. insulana

These two species are the most important pests of cotton in India causing heavy losses to the crop every year. E- vitella is abundant in high rainfall areas, where as E- insulana abounds in areas receiving scanty rains. The caterpillars of Earias. bore into the stem portion of young seedlings and apical shoots and later eat into buds, flowers and bolls. The attacked shoots wither, droop and ultimately die.

Control : The attacked shoots and bolls should be collected and destroyed. Avoid growing lady’s finger during the offseason in the vicinity of the cotton fields. Insecticidal control of the pest consists of spraying is done every 15 - 20 days of monocrotophos, endosulfan or malathion.

II. Pests of Paddy

a. Rice stem borer - Tryporyza incertulas

This pest bores into the stems of the young mature stages of paddy.

b. Rice bug - Leptocorisa acuta

It is the most important pest of paddy in India. It mainly feeds on paddy but is also found feeding on millets, maize, sugar cane and some grasses. The adults and nymphs feed on the milky juice of the forming grains which as a consequence become chaff.

Control: In nurseries and fields, the leaves of paddy plants containing eggs should be clipped and burnt. As the bugs feed and breed on various types of grasses, removal of such grasses from the fields will help in reducing the population. Collection of bugs with a hand net and their destruction is a useful mechanical method. Among the insecticides BHC and malathion as dusts and carbaryl and methyl parathion as sprays just before flowering of the plants are effective.

III. Pest of Sugarcane

a. Indian sugarcane leaf hopper - Pyrilla perpusilla

This pest sucks the cell sap of leaves

b. Sugarcane root borer - Emmalocera depressella

This pest causes damage to the stem below the soil surface

c. Sugarcane shoots borer - Chilo infuscatellus

This pest causes damage to the shoot

d. Sugarcane top shoot borer - Scirpophaga nivella

It is one of the most destructive pests of sugarcane.It is found all over India. The damage by the borer actually starts from the mid-rib of the top leaves into which it bores and makes tiny holes. When the growing point is damaged, side shoots are formed in the young plants and bunchy tops in the orders ones. The quality of the juice is also affected.

Control: Effective control of this pest is possible only by integrating mechanical and chemical control methods. Mechanical methods include the collection and destructions of egg masses and affected top shoots and sowing of resistant varieties. The chemical methods involve application of 4 % carbaryl or endosulfan granules in the leaf whorls or spraying of 0.05 % monocrotophos or 0.1 % endrin

IV. Pests of Vegetables

a. The red pumpkin beetle - Raphidopalpa foveicollis

This pest causes damage to the leaves, flowers and buds of younger plants.

b. Cabbage butterfly - Pieris brassicae

This pest causes damage to the leaves

c. The Hadda beetle - Epilachna dodecastigma

This pest causes damage to the leaves of the brinjal, potato and tomatoes

d. Brinjal shoot and fruit borer - Leucinodes orbonalis

It is the most important and destructive pest of brinjal and has a countrywide distribution. The pest starts damaging the brinjal plant a few weeks after its transplantation. When the shoot is attacked by the caterpillar it droops and withers, finally drying up. When the petioles of the leaves are bored into by the larva the

leaves wither and drop. The attacked fruits show holes plugged with excreta on them. Upton 70 % loss of crop is caused by this pest

Control: Prompt collection and destruction of the plant parts harbouring larvae help in reducing the infestation. Insecticides such as carbaryl, endosulfan, Lindane and diazinon, when applied at regular intervals give relief from heavy infestation.

V. Pest of Coconut palm

Rhinoceros beetle - Oryctes rhinoceros. It is distributed throughout South East Asia, Southern China, Philipines and south Pacific Islands. The adult causes infestation by feeding the young leaf fronds. They make burrows and throw out a fibrous mass. The infestation is marked by a number of holes on the fronds, when they open out. The attack results in the destruction of growing plant as a result of which the tree dies.

Control: The beetles should be destroyed by inserting specially designed hooked rod. In earlier developmental stages beetles should be destroyed by tackling the breeding places like manure pits near gardens by spraying 0.01% aldrin.

VI. Pests of Stored grains

Fig.10. Pests of stored grains

a. Rice weevil - Sitophilus Oryzae

This is a very serious major pest of stored grains in farm storage. It is worldwide in distribution. Generally, infestation starts in grains only during storage which may lead to heat spots in the grain. The grains are hollowed and the weight is reduced.

Control: The weevil is unable to breed at a grain moisture content of 9 % or less. Hence dry storage of grains can avoid infestation by the pest. The larvae and adults are killed by exposing them for 48 hrs. To the vapours of ethylene dichloride- carbon tetra chloride mixture under gas - proof covers. Fumigation of infested grains with methyl bromide is also effective and kills all stages of pest including eggs.

b. Khapra beetle - Trogoderma granarium

Khapra beetle is a very serious pest of wheat and other stored grains all over India. Only the larval stage is destructive, adult beetle being harmless. The grubs attack the germ portion of the grain. In severe infestation the cereals are reduced to mere frass

Control: Stocks of grains should be stored in thoroughly clean and insect-free stores which are regularly aerated. Before storage of grains, the godowns should be properly disinfected with benzene hexachloride smoke or fumigants.

c. Pulse beetle - Callosobruchus Chinensis

This is a very important pest of various pulse crops in India. It affects both in fields and in stores. The pest attacks leguminous pods in the field from where they are carried to godowns. The larvae bore into the pulses and grains. They feed and grow inside. The damaged grains are unfit for human consumption.

Control: Control can be achieved by growing susceptible crops at least a kilometer away from storage godowns which are the main source of infestation. Fumigation with methyl bromide in the godowns is very effective but proper care must be taken because of the high toxicity of this compound.

VII. Pests of household goods

Fig. 11. Pests of household goods

a. Termites (white ants) - Odontotermes obesus

There are more than 2000 species of termites. The food of termites consists primarily of wood (cellulose). This habit of termites is the cause for very serious losses, particularly in tropical countries. They destroy wood work, furnitures, buildings, fences and other wooden structures that come into contact with the soil. The losses caused by termites to Indian agriculture and other commercial crops are extensive. About 40 species of termites are injurious to economic plants such as wheat, barley, maize, gram, sugarcane, groundnut, several vegetables, fruit trees and coconut in India.

Control: The seriousness of their attack demands immediate control. For termite control, insecticides should be applied to the soil. Emulsions of1 % chlordane, 0.5 % aldrin and 0.5 % heptachlor are suitable for soil treatment. 5 % pentachlorophenol is good for wood preservation. The application of a mixture of BHC and aldrin to soil in the foundations of a building is effective.

b. Silverfish - Lepisma saccharina

It is cosmopolitan in distribution. It is commonly found living in moist warm places and among old books. It is a whitish wingless insect of about 13 mm in length It mostly attacks old books and magazines. It infests starched clothes, rayon fabrics, book labels or bindings where glue has been used.

Control : The books should not be kept in damp places. Books should be exposed to sunlight frequently. Dusting of 5% malathion has proved to be an effective control measure for heavily infested cases.

References

T. Sargunam Stephen, Biology (Zoology). First Edition – 2005,  Government of Tamilnadu.

مواضيع ذات صلة

قناديل البحرJellyfishes

ORIGIN OF LIFE- THEORIES

Geological time scale

Origin of life

Introduction to Genetics

Beneficial animals

Developmental Biology

Zoology

Wildlife Biologist

Turtle

Tunicate

Tuatara