Insects Harmful to Man

[Music] [Applause] [Music] insects make up 3/4 of the many thousands of different kinds of animal life most insects have no direct effect on man and some are helpful but there are others whose activities are harmful most harmful are those that carry disease closely related to the harmless math is the Anopheles mosquito which spreads malaria the mosquito lays its eggs and water the eggs hatch into larvae which swim above feeding and growing coming every so often to the surface to breathe the larvae change into pupae and from the swimming QP the adults eventually emerge [Music] the female feeds on animal blood to obtain the food needed for her aides to enable her to do this she has a sharp needle-like hollow structure called a proboscis [Music] this pierces the skin and through it is passed the fluid that keeps the blood from clotting it is this fluid that contains the germ which causes malaria in man because mosquitoes spend all but their adult life in water they can be controlled at the larval stage water and malarial regions is regularly patrolled and thousands of lives are saved each year by preventive measures [Music] plants are cleared from rivers to keep the water flowing and oil is sprayed to keep the larva from breathing [Music] another active blood sucking and disease-carrying insect is the tet see fly which is about the size of the blowfly the tet see fly is a serious problem in Africa because it spreads sleeping sickness as the mosquito spreads malaria some animals are affected as well as human the female lays fully formed larvae which go into the pupil stage almost immediately control is therefore very difficult please to feed on blood they're so small that they can live on the bodies of man and animals moving about between the hairs which hide their flattened bodies epidemics of plague and typhus are still carried demand by the tropical rat flea bedbugs are yet another group of blood sucking insects although bedbugs don't spread disease they live in mattresses in beds causing irritation and loss of sleep since house flies don't feed on blood they don't spread disease directly but they do so indirectly causing illness and man by contaminating food they eat most kinds of plant and animal matter dissolving the food with their saliva and sucking up the juices in this way germs from the Flies earlier meals are spread over the food this is why food should always be protected from houseflies some insects harm domestic animals this cow which seems healthy is infested with the larvae of the warble fly the warble fly lays its eggs on the animals leg the larvae traveled through its body and finally burst out of its back millions of elm trees have been killed by Dutch elm disease which is spread from Crete a tree by the European elm bark beetle the bark beetle lives just below the bark of trees and feeds on the living wood they are specially adapted for tunneling their hard wing cases are used as shovels first the beetle digs a central chamber for mating then the female tunnels away from the chamber laying eggs as she goes when the larvae hatch they eat away from the main chamber at right angles producing a pattern of tunnels that spread out in all directions bark beetles eat living wood there are other beetles whose larvae live on dead wood used for buildings and furniture these old Timbers from a church tower are full of holes made by the larvae of the Deathwatch beetle over long periods of time so much wood is eaten away that its strength is lost the Deathwatch beetle gets its name from a ticking noise made by the adult as a mating call [Music] although the holes made by furniture beetle larvae are smaller they do a great deal of damage they are often known as woodworm the larvae eat their way through the wood and when they are fully mature the adults emerge from the hole not so common but a serious past is the house long horn beetle which lives an aged lumber this piece of wood has been sawed a cross to show the large holes made by this fence [Music] look at the gnawing mouth of this long horn beetle larvae like most beetles the adult longhorn beetle can fly so the pests can spread rapidly in crop achill countries great damage is done to the structure of buildings and other materials by termites which gradually eat away all the wood notice all the termite droppings man's food both growing crops and stored food is also eaten by insects some beetles can even live in dry flour the Sawtooth beetles are often found in granaries the Sawtooth beetle gets its name from the saw like edge of its upper body adults and larvae feed on the grain and can move very quickly [Music] the weevil is a beetle that is well adapted for life in stored grain its head is stretched into a long beak or snout the grain weevil spends its larval stages inside a grain and finally emerges leaving only the husk a fits damage growing crops these cabbages have been attacked by the cabbage aphid although they are very small insects Athens multiplied rapidly into huge numbers and caused much damage to the plants on which they feed they also spread disease see how many there are these are all females which can produce more females without even mating [Music] black fly is another kind of aphid and is often found on beans a Fitz collect where the SAP of the plant is plentiful along the leaf veins and on the plant stem they insert their trump-like proboscis into the plant and suck up the SAP but more serious as a disease spread by aphids and this sugar beet field just one or two plants are affected by a disease called virus yellows so serious is this that the farmer will spray the crop with insecticide to keep the disease from spreading there's a wide variety of insects that feed on plants locusts have been feared for thousands of years notice how quickly these locusts feed and imagine a plague of millions of them locusts are most common in warm country in cooler climates there are pests such as the caterpillar of the cabbage white butterfly these larvae eat cabbage leaves almost constantly from the time they hatch out of the eggs until they spend their chrysalis however nature provides its own balances many caterpillars are killed by the apat Alize fly which lays its eggs and their bodies eventually the caterpillar is destroyed when the apat Alize larvae emerged to spin cocoons only a small number of cabbage white caterpillars escape to become pupae themselves emerging finally as butterflies this example of biological control reminds us that although many insects are harmful to man others are helpful and all are part of the delicate web known as the balance of nature [Music]