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INSECT PEST CONTROL METHODS

INTRODUCTION

Insects often interfere with the plans, desires and needs of Man. Such interference may be severe enough to result in morbidity and mortality through diseases, hunger, malnutrition and eventual starvation. With these facts, people often conclude that all insects are “Bad” and should be eliminated whenever possible. However, while it is true that certain insects or groups of insects cause significant problems for humanity, the proportion of these insects species is small compared to the total number of insect species (about 800, 000 species).

Insect pests reduce yield of crop plants or lower the values of the crops through contamination and reduced marketability. The insect activity most commonly responsible for this crop damage is the result of feeding by the insect. Insects are well known either as pests of agricultural crops or vectors of human and animal diseases. They cause agricultural losses and can cause suffering on man and his animals. In efforts to stop or reduce the losses or injuries caused by these insects, various control measures have been devised and are being used. The following are some pest control methods.

METHODS OF PEST CONTROL

a)      CULTURAL CONTROL

This involves the manipulation of the environment to make it less favorable for the pest populations. It can also be said to be the modification of the environment making it less suitable or attractive or conducive for pests through standard cultural practice. These techniques are ancient and vary with the culture, crop and pests involved. The results are not immediate, and these practices must be applied long before economic damage is evident if their impact is to be maximized. These processes do not require the use of machines or equipments instead a good understanding of the insects is required. The major techniques include;

i)                    Crop rotation

ii)                  Strip-cropping,

iii)                Destruction of volunteer plants,

iv)                Pruning of trees,

v)                  Various planting and harvesting techniques

vi)                Removal of previously infested crop residues

vii)               Water management,

viii)            Tillage.

These practices are relatively cheap, simple to employ, and yet vital practices. It will help in reducing pests from a farm land and yield good produce of crops.

 

b)     LEGISLATIVE/LEGAL (REGULATORY) CONTROL

Obviously, insects pests cannot be expected to comply with governmental legislation rulings, however dealing with the manufacture of goods, raising of crops and marketing practices can and often do, play on important role in the introduction and distribution of insects pests and the disease they carry. Regulations governing the importation of goods and food stuffs are the first line of defense against exotic pests. The problem of exotic introductions will continue as tourism and travel among the public and as trade between countries increase. Quarantine often involves different level of government, depending upon the perceived threat. Other attempts to eradicate exotic introductions have failed because quarantines by themselves are not effective long term techniques. Failure often comes when the eradication components, particularly those that use chemicals, come into direct conflict with values of the public.

Legal methods are methods of control where government legislation/laws have been passed so that certain control measures are mandatory with failure to comply being an offence. Those are extreme measures and only apply to certain very serious pest situation of natural importance. Such laws include:

i)                    The plant quarantine act of 1912

ii)                  The Federal Insecticide, Fungicide and Rodenticide Act (1947)

iii)                The Federal Food, Drug and Cosmetic Act (1954)

iv)                The Environmental Protection Agency (EPA) (1970)

v)                  The Federal Environmental Pesticide Control Act (1972) & (1978) and many more etc.  

     

c)      CHEMICAL CONTROL

Pesticides are chemicals designed to combat the attacks of various pests of agricultural crops. They fall into the following classes

1)      Insecticide

2)      Fungicides

3)      Herbicides

To most people, the concept of insect control is synonymous with the use of insecticides. A wide range of technique other than chemicals is available for suppression of pests. Apart from the pesticidal (pest killing) chemicals so commonly considered are other chemicals uses such as;

-          Repellents,

-          Attractant,

-          Sterilants,

-           Growth regulators.

Insecticides: These are pesticides that are specifically toxic to insects. As mentioned earlier, other types of pesticides include; herbicides (for plants) nematicides (for round worm) motuscicidas (for snails and slugs), Rodenticides (for rants and other rodents) and algicides (for algae).

BENEFITS FROM PESTICIDES

1)      Benefit to the farmer: Use of pesticides may increase the quantity and quality of agricultural produce. Fertilization alone increase the agricultural production by 19% and pesticidal spraying by 15%

2)      Reduction of Loss during Storage of Food Grains: The farmers store their excess agricultural produce for fetching more prices during the period when there is scarcity. They spray or dust the food grains with pesticides to protect from pest damage, by doing this the stored food grains can be used for a long time.

3)      Public Health: Pesticides play a very important role in public health operation and disease control in human. In public health insecticides are used against control of vector born diseases, malaria, filariasis and schistosomiasis.

4)      For protection of material: Insecticides are incorporated into plants, timber, plastic, sheathing etc. to prevent attack by insects. Used in industry for control or hazardous vegetation in forest and airport.

5)      Pesticides are routinely employed in the field of domestic hygiene to control flies, cockroaches, bedbugs, fleas and other pests.

6)      Pesticides are used as ectoparasictes in veterinary practice.

 

PROBLEMS OF PESTICIDES

1)      Pesticides residues have detrimental effect on human animal and plant.

2)      Development of resistance to insecticides among more than 250 insects species of both agricultural and medical importance

3)      Some are highly toxic to man and his animals.

4)      Disruption of the balance of nature between the insects pest and their natural parasite and predators which eventually perish through intensive insecticide applications and this has often resulted in the appearance of new insect pests.

5)      Environmental pollution by pesticides that arousal much concern in recent tears

d. BIOLOGICAL CONTROL

Definition: Biological control can be defined as the control of insects by insects. Biological control is sometimes applied only to control insect pests through the use of the insect predators and parasitoid of pest species. Biological control in the broadest sense, include all methods which reduce pest damage without the use of chemical pesticides, or which directly reduce pest populations. Within this contest, biological control encompasses resistant crop varieties, pest habitat modification and the use of pheromones and growth inhibitors. Biological control involves the use of Natural enemies and the technique of sterile male release. Biological control uses both entomophagus insects and entomopathogens. Entomophagus insects include parasites and predators. Not all insects are harmful; among the beneficial species are those living at the expense of insects which are troublesome to us.

Biological control is the restriction of the number of an animal or plant by natural enemies and this illustrate some aspects of the study of natural enemies and their use in the control of insect pest (Pierrard, 1993). Biological control can be used against all types of pest including vertebrates, plant pathogens and weeds as well as insects. The methods and agents used are different for each type of pest.

METHODS USED IN BIOLOGICAL CONTROL INCLUDES

i)                    The use of Natural Enemies of pest insect.

ii)                  Use of genetic and sterility in insect control.

iii)                Use of sex attractants/insect Attractants.

 

(i)                 USE OF NATURAL ENEMIES OF PEST INSECTS: For almost every animal and plant that lives on land or in fresh water there is an insects or sometimes many that attacks it. Vertebrates are attacked by fleas, lice, and biting flies. Invertebrates have their own contingent of insect predators, parasitic wasps and flies. Plants are attacked by borers, leaf chewers, sap suckers and seed feeders. The significant concept to be derived here is that if the animal or plant being attacked by insect is considered a pest by human, then its own natural enemies can be regarded as beneficial to humans. Any suppression of the pest by its insect’s enemies will contribute to human welfare by suppressing the effect of the pest on humans.

This concept is the basis of applied biological control. Weeds like purple nutsedge (Cyperus rotundus L.) hedge bindweed (Convolvutus sepium L.) and Carduus spp. There is also a “natural control” (pest suppression without human intervention) that exerts an overall effect of staggering magnitude. It may be unnoticed by human until the balance is disturbed by pesticides, pollution, or other factors and the resultant population explosion of pests ensures.

If a pest population begins to build up in an area, then the pest’s own pest (its natural enemies) should also start to build up. The natural enemies should be on the increase because there are more food resources (the pest) available. The outcome of such as occurrence logically should be reduction of the pest by its natural enemies so that it no longer is at the economic threshold, and can thus by tolerated. Natural enemies play an important row in limiting potential pest populations when a non-toxic control method is used, natural enemies are more likely to survive and reduce the numbers and damage of potential pest species.

There are three categories of natural enemies of insect pest, namely;

i)                    Predators,

ii)                  Parasitoids and

iii)                Pathogens

·         PREDATOR: Predators capture and consume succession of living individuals or prey.  Insects are an important food for many vertebrates, including birds, amphibians, reptiles, fish and mammals. Those insectivorous vertebrates usually feed on many insect species, and rarely focus on specific pests unless they are very abundant.

Important insect predators include lady bud beetles, ground beetles, rove beetles, flower bugs praying matids and other predatory true bugs, lace wings and lower flies. Spiders and some families of mites one also predators of insects and mite pests.

·         PARASITOIDS:  Parasitoids are insects with an immature stage that develops on or in an insect, and ultimately kills the host. Adults are typically free living and may be predators. They may also feed on other resources, such as honey dew, plant nectar or pollen. Because parasitoids must be adapted to the life cycle, physiology and defenses of their hosts, many are limited to one or a few closely related host species. Thus accurate identification of the host and parasitoids species is very important if you use parasitoids for biological control

PATHOGENS:

Insects, like other animals and plants, are infected by bacteria, fungi, protozoan and viruses that cause disease. These diseases may reduce the rate of feeding and growth of insect pests, slow or prevent their reproduction, or kill them. In addition, insects are also attacked, by some nematodes that, along with the bacteria they carry, cause disease or death. Under certain conditions, diseases can multiply, and spread naturally through an insect population, particularly when the density of the insects is high. An example of an insect pathogen that has been successfully controlling its host is the fungus

Entomophaga maimaiga, a pathogen of the gypsy moth. This fungus was introduced about 1911, but was not recovered in forests until 1989, when it was widespread and abundant in New England. It has continued to control New England gypsy moth populations for several years. It over winters in leaf litter as resting spores, which germinate when gypsy moth larvae are present. Newly hatched caterpillars are dispersed by wind, and those that fall to the forest floors are probably infected while crawling to a tree. While these larvae are feeding in the tree canopy if there is enough rainfall, the fungus in their bodies produces spores that spread to other caterpillars. If conditions are right, this infection cycle occurs again during the larval stage. Large caterpillars rest during the day in forest litter, where they are also susceptible to infection. In late June, as infected caterpillars die in large numbers, new resting spores are produced to survive the next winter. This biological control process depends on well timed rainfall to be successful.

ii. Use of Genetics and Sterility in insect control. Reproduction in pest insects can be disrupted by releasing sterile or genetically altered insects into natural populations. This approach of using insects for self-destruction is known as Autocidal Control. Utilizations of these techniques are dependent on our ability to produce economically large numbers of insects into natural populations. Also the insects released must be successful competitors with member of the natural population for mates. Several genetic mechanisms exist that can at least theoretically reduce the reproductive capacity of pests. The use of lethal mutations involves introduction of genes that are lethal under certain conditions when the specific conditions occur a breakdown in normal physiological function occurs. The first and best known sterile insect program involved eradication and suppression of the screw worm, a fly attacking life stock. It was initiated by knipling and his associates in the U.S. Department of Agriculture.

Also the arrival of new world screw worm fly in Libya in 1988 that produced a grave threat not only to Libya but to the Africa continent as a while was completely eradicated by the saturation of the infested zone with sterile flies.

iii. Use of Sex Attractants:

These are chemicals produced by female insects when they are ready to mate. The chemicals are detected by the male even in minute quantities and follow the odour to the source. This has been used to trap males and brought to their death by using female sex attractants, these chemicals are called Sex pheromones it is well known in many insects especially among Lepidoptera e.g. is the Actias selene moth. Synthetic pheromone of Spedoptera litloralis is now used in cotton fields for monitoring moth population and mass trapping and the disruption of pheromonal communication between sexes with very encouraging result in Egypt.

Note: The variety of chemical sources that attract insects is myriad. Foods, mates, oviposition sites, nesting sites, and prey habitat are among the many chemical emitting sources that affect one or more species of insects. Chemicals emitted by one individual of a species that cause behaviour in another individual of that species are termed “PHEROMONES”. Collectively the pheromones, allomones and kairomones are called “SEMIOCHEMICALS”. The first insect pheromone identified was the sex pheromone of the silkworm bombyx mori. As with most Lepidoptera, the female moth produces and emits a pheromone when she is physiologically receptive for mating. The male, often with its relatively more elaborate antennal receptors, hornes in on the source of the pheromones the female and mating occurs. Although the silkworm’s pheromone (bombycol) was not found until 1959 the attraction of male moths to females because of odor has been known for many years. Since the 1st isolation of bombycol a whole series of sex attractants have been identified. Since each species of insect typically has its own unique sex attractants. Classes of attractants other than pheromones are also being investigated for their potential use in pest suppression. In biocontrol, the arrestant kairomones emanating from caterpillar frass (feaces) have been identified and are being used to cause the pest parasitoids to search for their hosts more diligently in low density situations. Food lures for Mediterranean fruit fly, Japanese beetle and yellow jackets are being used commercially in control programs.

 CLASSICAL BIOLOGICAL CONTROL (CBC)

This process requires extensive research into the biology of the pest, potential natural enemies and their biology, and possible unintended consequences (e.g. Negative effects no native species that are not pests or no other natural enemies of the pest). After suitable natural enemies are found studied and collected, they must undergo quarantining to eliminate any pathogens or parasites on the natural enemy population. Then, the natural enemies are carefully released, timing their arrival with the enemy pest life cycle, in a site where the target pest is abundant, and where they will do well. Although this process is long and complex, when successful, the results can be impressive and permanent.

One of many examples of a pest controlled by successful introduction of natural enemies is the alfalfa weevil. The alfalfa weevil is a native to Europe, and was first reported in the United State about in 1904. It appeared in the eastern united state about 1951, and by the 1970s was a major pest across the country. Larval densities were high enough to require most growers to spray one or more times per year. Several parasitoids were introduced against the weevil. The most successful were two species of parasitoids that attacked the larvae, one that attacked the adult, and a parasitoid and predator that attacked the eggs. In addition there was a control program to collect natural enemies, rear them in large numbers, and release them. These natural enemies, plus a fungal disease that infects larvae and pupae, has kept weevil densities in the North east for below the economic injury levels. The success of this biological control was enhanced by cultural methods, such as timing cuttings to reduce weevil populations and avoid disruption of natural enemies. In addition, introductions of other natural enemies of alfalfa pests and pest-resistant alfalfa varieties minimized insecticides use against alfalfa blotch leaf miner and aphids. This also allowed natural enemies of alfalfa weevil to flourish.

Classical biological control (CBC) is the introduction of exotic predators and parasitoids which are the natural enemies to combat the effect of insect pests, though the pests may have been introduced accidentally, causing great damage to agricultural crops.

CBC is defined as the conscious use of a natural enemy to reduce pest population below the economic injury level. It is recognized as one of the oldest and most sophisticated method of suppressing pest populations. Classical biological control has proved to be a successful approach here in Africa.

Among many adverse factors which continually affect every insect species in the struggle for existence are the other living things that feed upon it. There are collectively known as its natural enemies. The fact that man has during the best few centuries, learned something about the habitats, ecology and interrelations of insects enable him to take sides in the constant warfare that insects are carrying on against each other.    

STEPS FOR CLASSICAL BIOLOGICAL CONTROL

i)                    Collecting parasites or predators in places where they have naturally developed or assembled in great number and releasing them in places where they may do the most good.

ii)                  Collection and storing or handling the host insects in such a way to kill them but permitting parasites or predators among them to escape.

iii)                Raring under favourable conditions great number of parasites or predators and releasing them, whenever and wherever needed especially at the time when the normal fluctuations of the pest insects have reached their point of greatest abundance.

iv)                Importing parasites and predators or diseases from a foreign country which is extensively used.

 

ADVANTAGES AND DISADVANTAGES OF CLASSICAL CONTROL

Advantages of CBC over other methods of control includes;

i)                    Absence of toxic effects

ii)                  No development of resistance by the pests

iii)                 No residues of poisons in the environment

iv)                No build up toxins in the food chain

v)                  No killing of pollinators or development of secondary pests through the destruction of their natural enemies

vi)                The permanence of successful biological control programmes where repeated application of chemicals would be required.

vii)              The fact that biological control is self adjusting and does not require the careful timely and organization, which would be given to pesticides applications, and which often make it impracticable on small peasant building in underdeveloped areas.

 

DISADVANTAGES OF CBC

The disadvantages of CBC include:

1)      The identity of pest must be clearly established, and the taxonomists need to be made aware of any biological differences, as well as morphological or anatomical differences between various pest species.

2)      Most serious pests are not indigenous to the area in which they are pests and so it is necessary to go back to their country of origin for suitable predators and or parasites for pessible introduction.

 

INSECT PEST MANAGEMENT

Early practices were aimed at minimizing damage, but with the advent of synthesized insecticides in the 1940s attempt became directed towards eradication. Despite these efforts, however, successful eradication of insect pest species and maintaining this isolation is rare except in the case of localized areas such as islands. Consequently, In the late 1960s and early 1970s a new era began when, as the result of concern for the environment and observed resistance of pests to insecticides, integrated pests management (IPM) reemerged as a dominant concept.

INTEGRATED PEST MANAGEMENT: This is the practice of regulating insect pest population to prevent outbreaks instead of attempting to eliminate them through the use of as many control strategies as possible without injury to humans and the environment. To accomplish this, effective regulation measures involves:

a)      A knowledge of the pest life cycle

b)      Number of generations per years

c)      Population densities and growth potential

d)     Density-dependent and independent factors

e)      All phases of crop production including economic

f)       To try and establish whether or not the pest has natural enemies