eChapters

All control measures are directed to bring down the nematode population low enough to raise the crop successfully and profitably. The choice of control measures to be taken depends upon the nematode species to be tackled and the crops involved.

1. Cultural methods 
The objective of these methods is to adopt suitable land management practices, so as to bring down the nematode population in the field to a low level, which may not cause economic injury to the crop or to keep the field free from parasitic nematodes by adopting suitable preventive measures. Besides causing direct damage to the crops, several nematode species are known to transmit many fungal, bacterial and viral pathogens, which aggravate the extent of damage caused to the crops. Many of these pathogens gain access to the host plants only through mechanical injury caused by the nematodes. By controlling the nematode parasites, the incidence of diseases caused by such phytopathogens can also be avoided to a large extent. Cultural methods, though may not give spectacular results within a short span of time of a single season or year, as in the case of chemical control measures, if followed over a number of years is sure to give encouraging results. Cultural methods include crop rotation, fallowing, ploughing, flooding, trap cropping, use of organic amendments, selection of seeds and seed materials, use of resistant and tolerant varieties etc.

‘Nematodes’, otherwise known as ‘eel worms’, ‘thread worms’, ‘round worms’, and ‘nemas’ are unsegmented, smooth-bodied, mostly minute, worm-like metazoan organisms. They are classified under the Phylum - Nematoda. The term ‘Nematode’ has been derived from the two Greek words ‘Nema’ = thread and ‘Eidos’ = form, which means thread-like organisms. At present, the nematodes, which are exclusively parasitic on man and livestock are studied under ‘Helminthology’ or ‘Parasitology’, while the plant parasitic or phytonematodes, as well as free-living nematodes are studied under ‘Nematology’, a branch of biological science that exclusively deals with nematodes. Cobb coined the term Nematology in about 1920.

Nematodes are ubiquitous and are found every where life can sustain. They can survive in any type of environment and are found from the arctics to the tropics and from the oceans to the top of hills. Though basically aquatic, nematodes have adopted terrestrial habits. They are mostly found in the soil around the rhizosphere of roots of plants. They constitute 80 - 90 per cent of all multicellular organisms and the number of nematodes may vary from 1.8 - 120.0 million per sq. m. of soil according to Kevan (1965). At present the number of established species is about 15,000, but there may be several thousands more.

For effective and economic control of pests, besides selection of appropriate plant protection chemicals, application of the chemicals at the most vulnerable growth stage of the pests and use of chemicals at the correct dosages, selection of proper plant protection appliances to carry out the operation is also of vital importance so as to ensure uniform application of the chemicals.
 
Plant protection chemicals are mostly used as sprays and dusts using sprayers and dusters respectively. However, in most of the cases spraying is preferred to dusting. Different types of sprayers and dusters are being used for these operations and in both, there are manually operated as well as power operated equipments and in sprayers there are both hydraulic and pneumatic types of sprayers.

The nature of the pesticide formulations to be used and the purpose for which they are used also determine the type of equipment to be used. Dusters are used for dusting insecticidal dust formulations; sprayers are used for spraying insecticidal liquid formulations; granular applicators are used to apply granular formulations; fumigators are used to apply fumigants to fumigate godowns, warehouses, rat holes etc.; soil injectors are used to inject pesticides at a particular depth of soil under pressure; flame throwers are used to throw flames at specified targets.

The chemicals, which can destroy pests or prevent their occurrence by their chemical action, are known as ‘pesticides’. Pesticides include ‘insecticides’, ‘acaricides’, ‘nematicides’, ‘rodenticides’, ‘molluscicides’ etc., which are used to destroy insect pests, mites, nematodes, rodents, slugs and snails respectively.

Pesticides have been used even before the time when man never knew how to read or write. Even before 200 BC, several substances were known to control pests. Sulfur, arsenic poisons, fluorine poisons, as well as some plant extracts and oils were used to control pests. However, these substances could destroy only a few specific pests.

Advances in the invention of pesticides

The invention of many of the present day pesticides started only after 1867. Paris green, a synthetic chemical was the first pesticide used to control the Colorado beetles of potato.  Up to  1939,  only  a few inorganic  chemical compounds and plant poisons were used as pesticides. Only after the Second World War much advances were made in chemical research. After the invention of DDT in 1939, a revolution had started in the field of pest control.  Following the introduction of DDT,  several other pesticides were identified and introduced for pest control. In 1941, BHC was invented by the British and French scientists. During the same period, organophosphorus pesticides were invented by the German scientists and parathion, malathion, demeton etc. were introduced.

Insect pest control includes all measures adopted to make the life of insects hard and ultimately to destroy them or to prevent their multiplication and spread. Such measures can be taken up before the appearance of the pests or after occurrence of the pests. To achieve this purpose, it is quite necessary to know the factors which favor the occurrence of the pests and acquire enough knowledge about the nature and life cycle of the pests, the vulnerable growth stage at which they can be effectively destroyed and appropriate measures of control. Control measures may be either preventive or direct.
Insect pest control is broadly classified under two different heads viz., natural control and applied control.

I. Natural control
    1.    Climatic conditions. Temperature, rainfall, sunshine etc.
    2.    Physical or topographic factors. Mountains, oceans, rivers, lakes, forests, deserts etc.
    3.    Natural enemies. Parasitoids, predators including insects, birds, mammals, reptiles etc.
    4.    Disease causing organisms or parasites. Entomophagous fungi, bacteria, viruses and other microorganisms.

Collection and preservation of insect specimens is the best way to study their morphology, habitat, distribution, host relationship and many other interesting features. Killing, mounting and arranging the insects in some particular sequence creates much more interest than merely studying museum specimens or looking at pictures. A collection of varied types of insects goes a long way in increasing the knowledge and understanding of the taxonomy of insects.

Not all insects are found in every season and in every place. Their presence mostly depend on the availability of the host, as well as the climatic conditions. Though many insects can be collected in any season, they  are  naturally  abundant  in  moist,  warm  weather,  especially  in the  spring and early summer. To get a good collection, insects have to be collected continuously in all the seasons of the year, from all plants and plant parts, from stored grains and food products. Several types of butterflies, moths, bees, wasps, beetles and flies can be collected from flowers, which they frequent to collect nectar. Many insects can be collected from leaves, stems, fruits, roots and such plant parts. Many insects are found in water and on water plants. Some are found in barks of trees or in decomposing organic matter. These insects have to be collected from different localities where they are found. Most of the insects are diurnal, while some of them are nocturnal. Some are attracted to light. So, a knowledge of the habits of insects is important in making a good collection. Sometimes better specimens may be obtained by collecting the immature stages and rearing them into adults wherever possible. Keeping records of pest collections may help Entomologists to forecast largescale pest occurrence.

Though many of the insect species are injurious to man, his crops and his livestock in different ways, not all the insects are injurious. Some insect species are beneficial to man in many ways.  A  few  are  productive insects and yield materials directly useful to man. Of these, the most important ones are the honeybees, which give honey and bee wax, the silkworms, which give silk and the lac insects, which give lac. Some other insects are useful to man indirectly in many ways.

productive insects

1. Honeybees (Apis species)
Order - Hymenoptera
Family - Apidae

Kinds of honeybees

There are five kinds of honeybees in India. They are :
Apis dorsata - the rock bee
Apis florea - the little bee
Apis indica - the Indian bee
Apis mellifera - the European bee
Melipona iridipennis - the dammer or stingless bee

One of the chief aspects of Entomology is the study of insects from the standpoint of their innumerable relations and activities affecting the interests of man. More than any other living organisms, insects have more intimate and complex relationship with man. It is well known that insects affect human interests both for good and bad. However, their injurious activities are of much greater concern to man than the beneficial aspects of their activities. Several insects are beneficial to man in several ways, both directly and indirectly and there are scores of other insects, which do not interfere with the interests of man in any way.

From the time man stepped into the domain of insects, a stifle has started between the insects and man. To meet his various demands for food, clothing, shelter and various other requirements, man cultivates various crops and raises many domesticated livestock. Unfortunately for man, insects also have started depending on these for their living. When the requirements for man and insects happen to be the same, a race is on for their survival and existence. Insects attack plants and livestock and cause extensive damage and economic loss. So, man considers such injurious insects as his enemy and to safeguard his interests tries to destroy them by various means. However, man’s supremacy and intelligence have not proved a match to the rapid propagation of insects and their various adaptations to withstand any hardship and adverse conditions. In the effort to gain an upper hand, it has not been possible for man to destroy the unwanted insects completely and the struggle is going on as a never-ending ordeal.

The classification of living organisms has passed through several changes and has reached the present stage with the gradual assimilation of more and more knowledge about them. The classification is mainly based on the anatomy, life style, habits, habitats, metamorphosis and such other characteristics. Though the concept of classification of living organisms was perhaps started by Aristotle between 384 - 322 BC, it was the Swedish scientist Carl Linnaeus (1758) who presented the classification, which was acceptable to most of the Taxonomists. He propounded the binomial nomenclature of naming each and every organism of animal and plant origin with a generic and species name. In his classification, he was consistent in using Latin names for all the organisms. He was the originator of a regular system of classification in which he recognized larger and smaller categories, the larger ones comprising of a varying number of smaller ones. Because of his contribution in the field of Taxonomy, he is rightly called the ‘Father of nomenclature’. A.D.Imms later modified the system to some extent in 1961. However, Brauer (1885) laid the foundation of the modern system of classification of insects. He was the first one to emphasize the fundamental division into primitive wingless insects, the ‘Apterygota’ and the winged or secondarily wingless insects, the ‘Pterygota’. The latest code on classification and nomenclature was approved and published by the ‘International Trust for Zoological Nomenclature’, London in 1964.

Protection from natural enemies and adverse environmental and climatic conditions is vital to safeguard insects and to this effect, insects possess a great variety of protective structures and mechanisms without which they cannot survive.

    i)    Food. Each insect species has certain nutritional requirements for the completion of life cycle. If the required food for any particular species gets reduced in a particular locality, that species will gradually disappear from that locality, though other environmental conditions may be favorable. Under normal conditions, there may be sufficient food for the insect to live on and continue its race. In the event of sudden increase in the population of an insect, the density of the population becomes too high to be supported by the food available in the area. Under such conditions, some individuals of the species either migrate to other suitable areas where enough food is available or else starve, if the species has limited power  of  dispersal  as  in  the  case  of  many  coccids.  According  to  the nutritional requirements insects are characterized as ‘omnivorous’ (feeding on different kinds of both plant and animal food), ‘carnivorous’ (feeding on animal food) and ‘herbivorous’ or ‘phytophagous’ (feeding on living plants). Those insects, which feed on many cultivated and wild species of plants, are termed ‘polyphagous’ (e-g) Locusts, grasshoppers, cutworms etc. If the feeding activities of a particular species of insect are confined only to plants of one botanical family, it is termed ‘oligophagous’ (e-g) cabbage butterfly - Pieris brassicae. When only a single species of plants constitute the food of a particular species of insect, it is termed ‘monophagous’ (e-g) Brinjal fruit borer.

Insects generally reproduce by laying eggs or ‘ova’. The initiation of growth inside an egg, which in most cases is preceded by fertilization, leads to a long series of changes, finally attaining the adult stage and in due course to sexual maturity and finally to reproduction of a new generation. This chain of events from the egg stage to death constitutes the ‘life history’ or ‘life cycle’ of an insect.

Eggs are laid singly or in batches of only a few or up to hundreds or  even thousands. Generally eggs are laid under conditions, where food is available for the feeding of the future young ones.  The eggs are generally smooth, elliptical or oval, but some have diverse shapes such as, disc-like, hemispherical, conical, globular, spindle and many other forms. The egg surface may also have a variety of textures. In some aquatic insects, the eggs are covered with a gelatinous secretion, which swells in water forming a jelly-like spawn. In mosquitoes, the lateral sides of the eggs are expanded, which serve as floats. Eggs vary in size, from microscopic to about 3.0 mm. in diameter and 5.0 - 6.0 mm. or even more in length.

The development of an insect is a continuous process, but on the basis of external manifestations, it is divided into definite stages. The stage within the egg is termed ‘embryonic development’, that after hatching ‘post-embryonic development’ and the changes of form during the post-embryonic development constitute ‘metamorphosis’.

Similar to animals of the higher order, insects also possess all important internal systems of organs necessary for the proper performance of the various vital functions. The most important of the systems are the alimentary or  digestive  system,  the  circulatory  system,  the  respiratory system, the reproductive system and the excretory system. The fundamental arrangement of the various organs is more or less similar in all insects and does not exhibit much remarkable variations as seen in the external morphological features. The dorsal blood vessel or heart runs along the median line immediately below the dorsal wall. The digestive system including the alimentary canal and its appendages lie in the middle, below the heart. The nervous chain lies below the alimentary canal and immediately  above  the  ventral  wall.   The  organs  connected  with  the reproductive system are found in the posterior region of the abdominal cavity on both sides of the alimentary canal.  Though these arrangements are characteristic of all Arthropods, including insects, they are quite different in the higher animals (Fig.23)

‘Integument’, the outer layer of insects consists of the ‘basement membrane’, ‘epidermis’ and the ‘cuticle’. One of the most important characteristics of insects is the presence of the rather hard, flexible chitinous exoskeleton or cuticle, which covers the entire body and provides support to the body. The exoskeleton of insects that is akin to the internal skeleton of vertebrates accounts for their size and shape. Movement is made possible by the division of the cuticle into separate plates or sclerites.  Primarily these  sclerites  are confined to segments and the sclerite of one segment is connected to the sclerite of the adjoining segment by means of an articulate called ‘suture’, a region in which the cuticle is very thin and flexible. The cuticle of each segment is divided into four primary sclerites viz., a dorsal tergum, two lateral pleura and a ventral sternum. The dermal glands present in the epidermal layer secrete the entire cuticle of the insect.

Like that of the body, the cuticular skeleton of the appendages is divided into tube-like segments connected to one another by articular membranes, thus creating a joint at each junction. Such joints enable the segments of the appendages, as well as those of the body to move freely.

In addition to the exoskeleton, an endoskeleton is also developed. This may be an infolding of the procuticle that produces inner projections or ‘apodemes’ equal to bones in vertebrates on which the muscles are inserted.

Insects came into existence in this world some 250 - 500 million years ago, while man appeared in this planet only about a million years ago and intruded into the domain of insects. From this time onwards, a rapport had started between the insects and man. Man considered insects obnoxious and not worth consideration in the early days. However, the real impact of insects on the activities of man became manifested to a greater extent only during the past few thousands of years. Gradually man began to understand the nature of insects and started looking at insects, both as his adversaries and as his beneficiaries. He started exploiting the useful insects for his own benefit and tried to destroy those, which are harmful to him.
 
There are numerous references in the ‘Ancient Epics’ and ‘Puranas’ such as, ‘Ramayana’, ‘Mahabharata’ etc. to show man’s acquaintance with insects even from very early days. Several references to insects are found in the ‘Holy Bible’ also. Ancient people of India were quite aware of insects, which provide honey, lac and silk. They were familiar with honeybees and gathering of honey and bee wax from hives. Honey was used in most of the religious rituals. Honey and bee wax were used in many Ayurvedic medicines against various diseases. The story of the lac palace constructed by the Cauravas to destroy the Pandavas by setting the wax palace on fire at night as narrated in Mahabharata is quite well known. The ancient Indians knew how to manufacture silk from silk thread produced by silkworms. Records show that an Indian king had sent some silken stuff to a Persian ruler even as early as in 3870 BC. References to insects such as, flies, beetles, bees, wasps, moths, ants etc. are found in old Sanskrit literature. The Ancient people also used some Mercury, Arsenic and Sulfur compounds for the control of some of the harmful insects. Numerous references to insects are found in the ‘Holy Bible’ also. King Solomon, the wise (971 BC), who ruled Israel had told his people to learn from the ways of ants, which are so active and orderly (‘Proverbs’, Chapter 6). He had mentioned as to how the ants gather and store food at the time of harvest, when food is available in plenty to be used in summer when food is scarce (‘Proverbs’, Chapter 30).

Accorinti, J.1983. Antifungal products from algal origin. Rev Int Ocean Med, 72, 45-53.
Allnutt, F.C.T. 1996. Cyanobacteria (Blue -Green Algae) Biotechnology: Past, Present and Future. Journal of Scientific and Industrial Research. 55, 693-714.
Ananthanarayan, R. and Paniker, C.K.J. 2005. Textbook of Microbiology (VII Ed.) Orient Longman Pvt Ltd, Chennai-600 002. pp 1-657.
Asthana, R.K., Srivastava, A., Singh, A.P., Deepali, Singh, S.P., Nath, G., Srivastava, R. and Srivastava, B.S. 2006. Identification of an antimicrobial entity from the cyanobacterium Fischerella sp. isolated from bark of Azadirachta indica (Neem) tree. Journal of Applied Phycology. 18, Number-1, 33-39.
Ayehunie, S., Belay, A., Baba, T.W., and Ruprecht, R.M. 1998. Inhibition of HIV-1 replication by an aqueous extract of Spirulina platensis (Arthrospira platensis). J. Acquir. Immune. Defic. Syndr. Hum. Retrovirol. 18, 7-12.

The objective of the present investigation was to evaluate the antibacterial properties of cyanobacterial species viz., Anabaena variabilis, Anabaena fertilissima, Nostoc muscorum, Nostoc punctiforme, Nostoc linckia, Nostoc commune, Spirulina platensis., Westiellopsis prolifica and Hapalosiphon sp. against some pathogenic species including Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pnumoniae and Salmonella typhi. The following are the major findings of the study.

    •    Extracts prepared in methanol were found more active as compared to ethyl acetate, hexane and dichloromethane.
 
    •    Antibacterial activity of extracts varied with the test organisms. Maximum antibacterial activity was shown against Staphylococcus aureus followed by Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi. Klebsiella pneumoniae was found to be least susceptible against all tested cyanobacterial extracts.

    •    Antibacterial activity was observed against both Gram-positive and a spectrum of Gram-negative bacteria by almost all the cyanobacterial species examined in the present study except Westiellopsis prolifica where activity was observed only against S. aureus, a Gram-positive bacterium.

Present work was aimed to determine the antibacterial activity and minimum inhibitory concentration (MIC) of active crude extracts of selected cyanobacterial species. Nine cyanobacterial strains viz. Anabaena variabilis, A. fertilissima, Nostoc muscorum, N. punctiforme, N. linckia, N. commune, Spirulina platensis, Westiellopsis prolifica and Hapalosiphon sp. belonging to family; Nostocaceae, Oscillatoriaceae and Stigonemataceae were selected from the herbarium of Indian Agricultural Research Institute, New Delhi, and maintained in BG-11 growth medium throughout the study in the laboratory.

In the present investigation, nine cyanobacterial species viz. Anabaena variabilis, Anabaena fertilissima, Nostoc muscorum, Nostoc punctiforme, Nostoc linckia, Nostoc commune, Spirulina platensis, Westiellopsis prolifica and Hapalosiphon sp. were tested for their activity pattern against some selected bacterial species.
 
Each cyanobacterial species was initially subjected to determine the early stationary phase of their life-cycle, which is believed to be the most appropriate period for the production of secondary metabolites by an organism. The growth curve for each cyanobacterial species was prepared by culturing them in BG-11 growth medium. Optical densities (OD) recorded at 650 nm were plotted against number of incubation days for each cyanobacterium. After 23-25 days of incubation period, each culture was harvested to obtain the biomass and spent medium, which were then subjected to process of extraction by using various solvents viz., Hexane, ethyl acetate, dichloromethane and methanol. The extracts and spent medium thus obtained were then investigated for antibacterial activity against five pathogenic bacteria including Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pnumoniae and Salmonella typhi.

Nine cyanobacterial strains viz., Anabaena variabilis, A. fertilissima, Nostoc muscorum, N. punctiforme, N. linckia, N. commune, Spirulina platensis, Westiellopsis prolifica and Hapalosiphon sp. were cultured in the laboratory. The growth curve for each culture was studied by growing them in Erlenmeyer flask using BG-11 growth medium. They were examined to determine the early stationary phases of their life-cycle, which are believed to be the most appropriate period for the production of secondary metabolites by an organism. After 23-25 days of incubation period, each culture was harvested and spent medium was collected by filtration of the biomass. Hexane, ethyl acetate, dichloromethane and methanol were used as the solvents for obtaining the extracts from biomass and spent medium of each culture which were then investigated against five pathogenic bacteria viz., Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Salmonella typhi. Antibacterial activity of different cyanobacterial sp. has been shown in various tables.

Culture Media and Reagents

The media used throughout the study were procured from Hi- Media Laboratories, Mumbai, India and the chemicals used were procured locally. Composition of each medium is as follows: