The measures for minimization of pest population depend upon agro-climates, land conditions, selection of varieties, local agro-economical systems and socio-economical conditions of the farmers. The conservation of natural enemies of pests and all the possible measures are adopted under BIPM.
Cultural Measures:
Cultural measures mean such cultural practices which do not allow the favourable conditions for life-cycle, growth and breeding of the pests. In this measures the practices like ploughing, sowing, irrigation and harvesting etc. are so managed that pest population does not cross the economic injury level. Such measures do not require special cost and input.
Here following measures and practices are adopted:
(1) Selection of Site/Crop:
For successful production of crops and trees, it is essential to select proper field and climatic region. The selected varieties should be tolerant to the pests of that particular climatic region. For example-Mythimna separata, Spodoptera mauritia and S. litura are found generally in all the regions but are specially seen in flooded area of some states after the flood recedes.
Citrus plants in sandy soils and waterlogged areas are more prone to pests. Ratooning of sugarcane in the gurdaspur borer (Acigona steniella) infested field is more prone of this pest. Irregular and unequal growth of the crop promotes the pest- infestation on smaller and younger crops.
(2) Ploughing:
Deep ploughing of soil exposes the hidden eggs and pupa of insects, nematodes, rhizomes and bulbs of the persistent weeds and other organisms which become food for their natural enemies. Some birds follow the plough or tractor at the time of ploughing is the good example. Insects in the pupal stages are helpless and are easily removed and killed. Summer ploughing by soil turning plough is specially useful in this respect. The type of equipment used for ploughing has also significance.
(3) Planting Material:
Many insect pest and diseases are transmitted from one crop to the next crop through infested/infected seeds or any other planting materials.
Therefore to grow new crop such certified seeds should be used which are free from all the insect-pests and diseases.
(4) Time of Planting and Crop Duration:
Adjustment in the time of sowing or transplanting helps in pest-control. Early sowing of mustard prevents from infestation of aphids. Gram sown before 15th of October shows less infestation of Heliothis. Late sowing of groundnut prevents from infestation of white grubs. Crops of the short duration give less chance to pest- infestation because these crops mature before the emergence of the pest.
(5) Destruction of Off Type and Volunteer Plants:
Off type plants is impure of new variety grown during the crop- production. Such off type is more susceptible to pest which is grown along with the standard variety. Potato tubers which are remained in the soil during digging, germinate early and attract potato cutworm (Agrotis segetum and other spp.). Ganganagar ageti (off type plant of cotton) is comparatively more prone to jassid (Amrasca biguttula biguttula) and pink bollworm (Pectionofora gossypiella).
(6) Destruction of Alternate Hosts:
Many plants especially weeds work as alternate hosts in off-season for insect pests and diseases. Paddy mealy bug, Army worm and fruit sucking moth spend their life on alternate hosts before attacking on main host crops. Tomato leaf curl virus multiply on parthenium.
(7) Thinning and Topping:
Such practices affect the pest-population. Topping of cotton removes the eggs of Heliothis armigera. Sowing of cotton, maize and hybrid millets at a higher seed rate saves the crops from pest-infestation. Unhealthy and infested/infected plants are removed through thinning.
(8) Prunning and Destruction of Crop Residues:
Unhealthy and infested portions of the fruit trees and horticultural plants are removed through Prunning and are collected and burnt. Prunning in citrus plants during April and May minimises the infestation of shoot borer. Burning of fallen leaves and stubbles in the mango-orchard kills the nymphs of mango mealy bug. Many insect-pests hibernate and hide in the crop-residues and stubbles in the cold season, later on who emerge after becoming adults. Therefore it is essential to destroy the crop residues completely.
(9) Fertility Management:
The crop growth depends on the soil fertility which indirectly affects the pests. Use of phosphatic fertilizer protects from jassid (Amrasca kerri) in lobia and H. armigera in gram. Normal and excess supply of potassium protects from pest-attack where as low dose of K promotes pest- infestation.
Excess of K increases the silica-content in the leaf due to which cell-wall of parenchyma and tissues containing epidermal sclerenchyma become hard and unfavourable for pest- attack. Excess application of nitrogen invites pest-attack. Use of Azospirillum sp. makes the plant hard against the attack of insect-pests and diseases.
(10) Water Management:
It is seen that in the flooded area the pests inhabiting in the soil are submerged, some are flown away and some are exposed to their natural enemies. Soil inhabiting pests like white grub and cutworm are reduced after the irrigation. The irrigation in sugarcane and wheat crop protects from white ants.
The attack of aphid (Lipaphis erysimi) is more in rainfed mustard after 47 days of sowing in comparison to irrigated. The deficiency of normal water in the plant increases the concentration of nitrogen and soluble sucrose in the phloem- sap, due to which aphid-infestation is more.
Excess of malic acid in gram brings resistance against Helicouerpa armigera. Irrigation decreases the malic acid concentration resulting in more of pod-borer infestation.
(11) Crop Rotation/Roto Cultivation:
Crop provides food for insect-pests and disease causing organisms and if the food is abundant all-round the year, such pests flourish and multiply rapidly. Their abundance depends upon the fecundity, hibernation, brooding period, dissemination capacity etc. Therefore the pest problem of the specialised farming will be different from the mixed farming areas. The pest-problem of monoculture can be controlled by adopting crop-rotation/Roto cultivation.
(12) Cropping Scheme and Trap Crop:
Certain pests may be controlled by using trap crops in the cropping scheme. Certain pests are more attracted towards certain crops. Such crops are sown in narrow strips around the major crop at a specified row distance are served as a trap for the pest that might be common to both.
The preferred host plants can be grown around the valuable main crop and when the pest has appeared, they can be cut and destroyed. Lady’s finger (Bhindi) is a good example of trap crop for cotton to attract jassids and cotton bollworms. To attract hairy caterpillar, sesame can be grown around the cotton.
To attract diamondback moth, leaf webber and aphids of cabbage, two rows of mustard are sown after each ten rows of cabbage. One row of mustard is sown after 15 days of transplanting and another one after 25 days. When the pest appears on mustard, spraying of 0.5% dichlorvos at an interval of 10-15 days can be done and the main crop (cabbage) is to be sprayed with neem based insecticide which protects natural enemies also.
Transplanting of yellow tall marigold (Tagets sp.) or bidi rustica tobacco (1:5) around the tomato is useful to control Helicoverpa armigera. H. armigera lays her eggs on yellow tall marigold which is exposed to egg-parasitiod Trichogramma chilonis.
Spraying of HaNPV or Bt (HaNPV → Nuclear Polyhedrosis Virus of H. armigera; Bt → Bacillus thuringiensis (bacterium)] is done on the main crop of tomato which is safe to Trichogramma. H. armigera on rustica tobacco may be controlled by Mirid predator named Cyrtopeltis tenuis. In the locust (Schistocera gregaria) affected areas, neem trees are grown to attract predatory birds.
(13) Use of Resistant Varieties:
It is well known that some crops are less attacked by pests because they have more natural resistance than others. They have some special characteristics like acidity or tasteless of cell sap, early maturity, hard bark etc. which help in building their resistance.
Mechanical and Physical Measures:
Such measures involve the use of physical components of environment or the use of labour with or without the help of special equipment. Such measures give quick result therefore these are popular among the farmers but it is laborious and time-consuming and not possible on large scale.
The important components are as follows:
(1) Destroying after Hand-picking:
Different stages of pest’s viz., egg, larva, pupa and insect itself are picked up regularly and are destroyed. It is the oldest method and is suitable for adults and egg cluster of lemon-butterfly, grubs of mustard sawfly and all stages of Epilachna spp.
(2) Use of Net or Screens/Barriers:
Outlets of the farm houses viz. windows, doors & ventilators are screened to prevent flies, mosquitoes, bugs etc. The net is used to cover the nursery of tomato and chilli to protect from transmission of virus through Bemisia tabaci. Wrapping of pomegranate fruits with butter paper or cloth protects from Anar butterfly. Wrapping of orange fruits with bamboo-baskets protects from fruit sucking moth. Coconuts are saved from monkey by planting thorny plants around the coconut plant.
(3) Temperature:
Almost all the insects are inactive at the low temp, between 60°F (15.5°C) and 40°F (4.4°C) and even at the lower temp. i.e., below 40°F (4.4°C) practically there is no damage by the pests. But higher temp is more suitable to control the pests than the lower temp. Steam sterilisation of glasshouse kills the soil pests (insects, disease causing organisms and nematodes). Simon cotton seed heater is used to kill the larvae of Pectinofora gossypiella in which cotton seed is treated for 3- 7 minutes at the temp, of 125 to 135°F upto 140°F (51.6°C- 57°C upto 60°C).
Bulbs are given Hot water bath treatment to destroy nematodes and mites. Blow lamp is used to kill the colonies of wooly aphids. Seeds and grains of godown pests and due to hot air treatment moisture content of seed is also reduced resulting in the increase in storage-life of seeds/grains. The empty godown may be given superheating above 50°C for 10-12 hours to kill hibernating pests.
(4) Use of Mechanical Traps:
Light traps are used for those pests who attract towards light. Such pests are white grubs, Agrotis, rice stem borer, leaf hopper etc. Blue cloth is used to trap (polyphagous) tobacco caterpillar (Spodoptera litura). Different types of traps are used to trap rats.
Pheromone traps viz. Cis-9, trans-11-Tetradeca dienyl Acetate for Spodoptera litura and S. littoralis; and Cis-9-, trans-12-Tetradeca-dienyl Acetate for Ephistia elutello and S. litura are used. To control crawling insect- pests on trees, banding materials are used which are of two types- (i) Sticky band (e.g. Ostico) and (ii) Slippery band (e.g. Cellophane). Greese bands are used to control mango mealy bug, wingless insects and ants.
(5) Use of Radiant Energy:
High Frequency radio waves (2450 mega cycles, 12.25 cm wavelength and 940 watts) generates temp, of 170°-187°F (76.6°C – 86.1°C) which is used to kill hibernating or hiding pests in godown like grainery weevils and confused flour beetles within 15-20 seconds only.
Radiant energy is indirectly used to make male insects sterile. Male insects are made sterile by using γ-radiation (gamma radiation) or chemo-sterilants and are released in the normal population of insects where such sterile insects compete with the fertile males for copulation with the female.
And thus population of insect-pests can be controlled. E. F. Knipling and Co. of USA in 1937 made the pupae of Screw Worm fly (Cochliomyia homini uorax) sterile on Curakao Island. He used the γ-radiation by cobalt-60 (60Co).
Such male sterile insects were released @ 400 males per square miles to get 100% sterile egg masses and the pests were completely controlled. This technique was known as Sterile Male Technique and thus E.P. Knipling was the propounder of the concept of genetic control of insect pest.
(6) Use of Drie-Die:
The Drie-die (prevalent in USA) is a very porous & fine silicagel. It desiccates water from the cuticle of insects resulting into death. It is used mainly for godown insect- pests.
(7) Spike Thrust Method:
Iron hooks are used to kill white grubs and adults of Rhinoceros beetle present in Coconut- crown. This method is spike thrust method and is also used for sugarcane stem borer and Mango stem borer.
(8) Removal of insect-pests by sieving and winnowing.
(9) Use of scintillating tapes to protect from birds.
(10) By making intense sound and shaking the pests.
Biological Control Measures:
In a natural or unperturbed perturbed ecological system the insect-pests and weeds are automatically controlled by their natural enemies. But in the perturbed ecological system predators, parasites, mites, fungi or any other organisms are used in excess to control different types of pests; which is called biological control measures. Parasitoid, Predators and Pathogens are used as the natural enemies to control insect pests but parasitoids and Predators are used more.
Parasitoid:
When an insect is itself a parasite, then it is called parasitoid e.g., egg parasitoids of Trichogramma chilonis and T. japonicum are used to control Tissue borers of sugarcane and Rice.
Primary Parasite:
Such parasite attacks on phytophagous insects.
Hyperparasite:
Such parasite attacks on primary parasite. Hyperparasite is also known as secondary parasite.
Autoparasite:
In some species of insects it is found that male insect attacks on female insect of its own species which is called Autoparasite.
Homeostasis:
Over a long time the population of pests become stable i.e. Homeostasis is the stability of pest populations over a long time. Pest populations may fluctuate temporarily but over a long range of time, they tend to be stable.
Predators:
Who hunts or kills other organisms for food, is called predator. The first insect scientifically employed for any biological control programme was the Vadalia beetle (Rodolia cardinalis) brought from Australia into California (USA) in 1888 to control the cottony cushion scale (Icerya purchasi) a serious pest of citrus.
However the first natural enemy to be introduced by man from one country to another was a Mynah from India to Mauritius in 1762 to control the red locusts. Chandra Shekhar Lohmi of India discovered a bug in 1975 which successfully controlled the Lantana camara a flowering weed of Nainital. This bug is known as Lantana bug.
Followings are the important in biological control:
(1) Conservation of Natural enemies.
(2) To release parasite/parasitiods.
(3) Use of Microbials/Pathogens.
(4) Use of Predators.
(1) Conservation of Natural Enemies:
Conservation and enhancement of natural enemies should be of first priority. If the natural enemies are properly conserved, the need of other control measures is greatly reduced.
Conservation means to avoid such measures which are harmful to natural enemies and to enhance those measures which are helpful in increasing their longevity, reproduction or to build up attractive habitat. Conservation becomes most critical when there is a small reservoir of natural enemies outside the cropped area.
Pupae of epipyrops are found in large numbers on the leaves and trashes of sugarcane at the time of harvesting. If these trashes/leaves are not burnt but are left around the harvested fields, the adults emerge to augment the supply of natural enemies in the pre-monsoon season against Pyrilla purpusilla on the young sugarcane crop. Cultural practices likes ploughing, mowing or burning of crop residues may be harmful to natural enemies.
The concept, ‘More is the diversity, ‘more is the stability’ holds true, since diversity may provide alternate hosts as source of food, sites in winter and so on. Almost all the pesticides have adverse effect on the natural enemies. Therefore good pesticide should be used and promote such predators who are relatively resistant to such pesticides different measures are so managed that the population of predators is increased. For predatory birds and wasps, artificial nests should be available and flowering trees having pollen and nector like Euphorbia, wild clover etc. should be planted at bunds.
(2) To release Parasite/Parasitoids:
For the effective control of the particular pest, the specific parasites or parasitoids are released. This method is the most effective and economical against pests those have only one or few discrete generations in a year. Massive release have been attempted in several programmes involving natural enemies like Trichoderma spp. and general predators like green lace wings and Coccinella septempunctata.
(3) Use of Microbials/Pathogens:
The micro-organisms like bacteria, virus, reckettsiae, protozoa, nematodes and fungi have the capacity to affect the pests, d’ Herelle utilized one bacterium named Coccobacillus acridiorum (Modern name-Cloaca cloaca VAT. acridiorum) isolated from desert locust Schistocerca pallens for the control of locust. However his work was not confirmed by the later scientists, though d’ Herelle may be named as the father of microbial control.
The term ‘microbial control’ was coined only in 1949 by Steinhaus. Bacillus thuringiensis (bacteria) is very effective in controlling many Lepidopterous larvae like cabbage worm, Pectinofora gossypiella, sugarcane stem borer etc. Bacillus popilliae causes milky disease in Japanese beetle. NPV (Nuclear Polyhedrosis Viruses) have the effective control over Spodoptera litura and Helicouerpa armigera.
(4) Use of Predators:
The coccinellid predator Cryptolaemus montrouzieri (Muls.) feeds on citrus mealy bug and grapevine mealy bug. The exotic coccinellid Curinus coeruleus Mulsant a shiny bluish- black ladybird beetle was introduced into India from Thailand in October 1988 to control subabul psyllid, Heteropsyla cubana crawford. Ducks are employed to control striped bug, Tetroda histeroides in rice crop.
The Euglandina rose and Gonaxis quadrilaterlis is employed to control Gaint African snail Achatina fulica. The predator Cyrtorhinus lipidepennis (Miridae) feeds on all developmental stages of brown plant hopper (BPH) but primarily on eggs. The wolf spider Lycosa pseudoannulata is also a potential predator in nature in rice ecosystem.
Due to increasing importance of biological control, many countries have now biological control stations that collaborate with each other to solve their pest control problem through natural enemies (biological control agents). The CIBC of India (Commonwealth Institute of Biological control) is the unit of CAB (Commonwealth Agricultural Bureau) with it’s headquarter at Trinidad (West Indies).
The CIBC, Bangalore came into existence in 1956 and since then it has imported over 100 species of insects. The function of the Institute (CIBC) is to furnish information on natural enemies of insect pests and supervise and supply biological control projects anywhere in the world.
Chemical Control:
Chemical control measure is the most prevalent amongst the different measures of pest management. For the effective and balance use of minimum quantity of the pesticide.
There are two main principles:
(1) Use of selected pesticides.
(2) Need based use of Pesticide.
(1) Use of Selected Pesticide:
Physically and biologically selected pesticides are desirable from environment point of view. Monotoxic chemical kills only one species of pest and does not harm to other organisms, but such chemical is discovered very few. The main object in selecting pesticide is that the selected one must be harmless and non-injurious to beneficial and non-targeted fauna and flora. Since very few such chemicals are available, therefore such measures should be adopted which minimise the hazardous and adverse effects of the pesticides.
These measures are:
(a) The minimum amount of pesticide should be prescribed.
(b) The chemical should be selected on permanent basis but at every time the pesticide of less strength should be used.
(c) The chemicals should be used in a planned way to kill targeted pests only and not harm natural enemies.
(d) Keep the surface rough at the time of transplanting so that beneficial organisms can escape in hollow places.
(e) Use the pesticide only when the pest population crosses the Threshold injury level.
(f) Only selective and non-persistent pesticides should be sprayed at soil that the natural enemies can be escaped from to come in direct contact.
Study on selective protection of recommended concentration of chemical pesticides revealed that endosulfan-22 in chlorinated hydrocarbon group is comparatively safer to natural enemies. Other safer pesticides are phosalone-29, monocrotophos- 12, oxydemeton methyl-11, dichlorvos-10 under organo-phosphate group. Botanicals or biopesticides, fungicides, acaricides, and herbicides are generally safe to natural enemies.
There are about 1005 species of plants which have insecticidal properties; 384 species have antifeedant properties, 297 have repellant; 27 have attractants and 31 species have growth inhibiting properties. Neem (Azadirachta indica). Pongamia globra and Mahua (Madhuca indica) are well known botanical pesticides.
Extract from neem seed-kernel (2-5%) is effective against rice cutworm, diamond black moth, rice brown plant hopper, rice green leaf hoppers, tobacco-caterpillar and different species of aphids. Mahua seed kernel extract (5%) is effective against sawfly and other insects.
(2) Need based use of Pesticide:
The Strategy of a good IPM Programme advocates need based use of pesticides rather than calender based prophylactic treatments. The pesticide should be chosen on the basis of its effectiveness and least injury to useful non-targeted organisms. The pesticide formulations, application measures and time of application are also important for effective IPM Programme.
The following points are to be adopted under chemical control measures:
a) Essential nursery treatment so that the population of pests borne in nursery can be minimised.
b) Minimum use of pesticide.
c) Proper care of nursery so that need based pesticides can be used.
d) The pesticide should not be used on calendar basis with some exception.
e) Use of proper amount of pesticide at proper time.
Pest Surveillance:
Pest surveillance is the fundamental tool in IPM for taking management decisions. It requires estimation of changes in the pest distribution and their abundance information about the life history of pests and influence of natural enemies; and the effect of climatic factors on pest populations. Vulnerable stages of the pest are ascertained. Their programme can be taken on the basis of area or at the farm level.
The use and misuse of pesticides has led to the problems of pest resistance and resurgence, distinction of beneficial organisms and wild life, pesticide residues in food, fodder and feed etc. Pesticide resistance management (PRM) is possible only when survey and surveillance of pest is carried out.
Forecasting of Pest Attack:
Ecology of pests is the basis for pest management. Regular pest monitoring, survey and surveillance is necessary to enhance the preparedness of the farmers to meet the challenges. The analysis of the agro-ecosystem under which the pests and their natural enemies thrive is vital. Forecasting of pest attack is essential for planning of successful management practices. The correct forecasting depends upon the vast knowledge of biology and ecology of the pest.
For the correct forecasting, following primary informations are essential:-
(i) Seasonal quantitative study,
(ii) Study of life-history of pest, and
(iii) Effect of weather and season on pests.
The seasonal quantitative study of pests reveals the ups and downs in their number (population), geographical distribution, and limit of the emergence in one season. The study of life history helps in finding out the important facts about the number of eggs laid down, place of egg-laying, time interval and food quantity taken by each instar, maturity period of female adults etc.
The weather/season directly or indirectly influences not only the crops but the population of pests their parasites, parasitoids and natural enemies also. The pest intensity from one crop to others is also affected by weather or season.
For successful IPM programme, the agro-ecosystem analysis on selected crops and the conduct of Farmers’ field Schools (FFS) have been gaining importance. Farmers are trained on IPM approach on their field, rice/vegetable fields or orchards to gain knowledge and skill as to how to grow healthy crops and to manage pests. Such schools are called Farmers’ field schools.
Quarantine Measures:
The method of exclusion of the pests, enforced through certain legal measures is commonly known as quarantine. Introduction of foreign pests is possible when agriculture produce, seeds, fruits and goods are imported. Partherium weed came into India with the import of Mexican wheat.
The pests problem also arises due to the transport of agricultural produce from one region to another. To stop the spread of such pests, the establishment of domestic quarntine is essential. For example the apples grown in the Kargil and Ladhakh areas of Jammu & Kashmir are not sent to outside because these areas are habitat of codding moth (Cydia pomonella). And due to such domestic quarantine the apple- industries of H.R and Kashmir valley are protected from the damage caused by such pests.
Varietal Control:
Selection of the resistant varieties is an important component of I.PM. It is essentially a preventive measure. The use of resistant varieties is the cheap and the best measure of pest control.
Gall midge and Brown plant hopper of Rice, Borer and scales of sugarcane, wheat rust, downey mildew of coarse grains, pulse viruses etc. have been controlled by the use of their concerned resistant varieties. Development of high yielding and pest resistant varieties are gaining importance throughout the world.
Varietal resistance against the insect pests is grouped into four categories:
(1) Tolerance
(2) Avoidance
(3) Non-preference, and
(4) Antibiosis.
(1) Tolerance:
In case of tolerance, the host plant is attacked by pests but there is little or no loss in biomass production or yield. Tolerance is mainly dependent upon growth capacity of the plant and the growth capacity is affected mainly by favourable conditions. In some cases, tolerant varieties show greater recovery than susceptible varieties from pest damage.
It is generally found that the attack of shootfly, stem borer or cutworm in germination stage aggravates their growth. The tolerance may be due to ability of the host to suffer less damage by the pest e.g., aphids in sugarbeet and brassica, greenbugs in cereals. Thus the use of tolerant varieties of agriculture is useful.
(2) Avoidance:
Pest avoidance (or disease escape) refers to the freedom of susceptible host varieties from the pests purely due to environmental factors. Avoidance may be a result of environmental factors, early varieties, changed date of planting, change in the site of planting, use of resistant root stocks, balanced application of NPK, control of pest carriers and control of pest itself. Early maturing cotton varieties may escape from pink bollworm infestation. Early sowing of mustard varieties escapes from aphid infestation.
(3) Non-preference:
Some varieties are unattractive or unsuitable for colonization, oviposition or both by the insect pest. This type of resistance is also known as non-acceptance and antixenosis. Non preference involves various morphological and biochemical features of host plants. Female insect does not lay eggs on non-preferred plant.
(4) Antibiosis:
Antibiosis refers to an adverse effect of feeding on a resistant host plant on the development and/or reproduction of insect-pest. In other words the lethal or harmful effect of plant on the biosis (life) of the insect-pest is known as antibiosis.
Such plants have characteristic features like hard and thick epidermis, hairy stems and leaves and above all the plant may be toxic. The morphological physological or biochemical features of the host plant either individually or in combination may attribute to antibiosis.
The capability of the disease resistance in plants is expressed in three ways i.e. the type of disease resistance:
(i) Disease Escape/Pseudo-Resistance:
Some crop varieties complete their life cycle before peak period of infection due to their characteristics of fast growth and earlier maturity. And thus such varieties escape from the development of lebilitating attack by disease causing organisms. Therefore it is called pseudo -resistance and escaping from the disease is Disease escape. For example early variety of wheat escapes from heavy damage by rust.
Early variety of potato escapes from the disease caused by Phytophthora infestans because attack of this disease occurs after the harvest of early potato. The crop in young or seedling stage is very susceptible whereas the fully developed and matured crop is unaffected which is known as Mature Plant Resistance.
(ii) Resistance:
Resistance is the ability to withstand (insect-pests and) diseases which may be conditioned by a number of internal and external factors operating to reduce the chance and degree of infection. In resistant variety, disease symptoms do develop and the reproduction rate is never zero (i.e. r#0) but it is sufficiently lower than one (i.e., r < 1). It means the development of disease in the resistance variety is very less which is expressed in the term of reproduction rate of pathogen i.e.-
0 < r < 1 or 1 > r > 0
(iii) Immunity:
The inability of parasite to infect the host even under most favourable conditions is known as immunity. The state of immunity is the absolute where the crop (host) is fully protected from infection. In other words such immune varieties neither allow the pathogen to develop nor show any disease symptom. Here the reproduction rate of pathogen is zero (i.e. r = 0) which is called Absolute Resistance.
According to van der Plank (1963) Resistance is of two types on the basis of physiological differences:
(a) Vertical Resistance/Perpendicular Resistance/Racial Resistance:
It is also known as race-specific, pathotype (biotype) specific or simply specific resistance. In this type, the resistance is effective against only one or some specific pathotypes or biotypes. It is generally determined by major genes (oligo-genes) and is known as pathotype specificity. Due to oligogenes, resistance is only for avirulent pathotype. In case of occurrence of frequent virulent pathotype, epidemics are common.
(b) Horizontal Resistance/Field Resistance:
It is also known as race-nonspecific, pathotype non- specific, partial resistance, General resistance. This type of resistance is effective against all the known biotypes or pathotypes. It is determined by polygenes i.e. many genes with small effects. Here reproduction rate is not zero but it is less than one i.e. r > 0 but r < 1. It means the symptoms of the disease appear but the rate of spread is slow, r.
Male Sterile Technique:
Male Sterile technique of pest control is known as genetic control under autocidal technique. The concept of genetic control was conceived by E.F. Knipling. For detail see ‘the use of radiant energy’. For making male insects sterile, γ-radiation obtained from cobalt -60 and chemo-sterilants are used. Chemo -sterilants are mainly derivatives of strong alkylating agent Aziairidine. TEPA [tris (1-aziridinyl) phosphine oxide] METEPA [tris (2- methyl 1-aziridinyl) Phosphine oxide] and Apholate [2,2,4,4,6,6, hexahydro-2,2,4,4,6,6.-hexakis (1-aziridinyl)- 1,3,5,2,4,6-triazatri-phosphorine] are common alkylating agents.
Male sterile insects made by radiation have shown less sexual competiveness whereas steriles made by chemosterilants have shown increased sexual competitiveness. Successful examples of male sterile technique by radiation are in fruit flies, Oriental fruit fly-Dacus dorsalis and Mediterranean fruit fly-Ceratit/s capitato. Upto some extent this technique has been used is melon fruit fly (Dacus cucurbitae), Onion fly (Hylemya antigua) cotton boll weevil (Anthonomus grandis) cockchafer (Melolontha vulgaris) cabbage looper (Trichoplusia sp.) Corn earworm (Heliothis zea), gypsy moth, codling moth (Laspeyresia pomonella) Chemosterilants have been successfully used in cotton boll weevil, red bollworm (Diparopsis castane) Pink boll worm (Pectinophora gossypiella) to produce male sterile. Male sterlie made by TEPA has been successfully employed to control Mexican fruit fly (Anastrepha ludens).
Use of IGR, Pheromones, Attractants & Repellants:
Juvenile harmone and chitin inhibitors are examples of IGR (Insect Growth Regulator) which affect insects only. Juvenile hormone (J H) inhibits developing adult insect under the pupal stage. JH is effective even if it is applied on the cuticle of pupa. It is secreted by corpora allata. Williams (1967) suddenly observed JH in the stomach of male Cecropia moth which has been chemically known as Neotenin.
This hormone when sprayed on the target insects at the suitable stage affects the metabolic activities and produces disorder in their reproduction and development resulting into death of the insects. Since it does not kill instantly, therefore it is not suitable to use at the time of outbreak of pests. Altoid, Kinoprene, Altozar etc. are commercially major IGR. Chitin synthesis inhibitor and Azadirachtin like phytochemical are proved good IGR.
‘Pheromones’ are such chemical substances produced by an organism exogenously which influence the behaviour or physiology of other member of its own species.
Pheromones are grouped as:
(i) Sex pheromones: such pheromones attract opposite sex.
(ii) Trail pheromones: such activate others to follow.
(iii) Aggregation pheromone: to get aggregation response.
(iv) Alarm pheromone: to alarm.
The word ‘pheromone’ was coined by Karlson and Butenandt in 1959 for a chemical that is secreted into the external environment by an animal and that elicits a specific response in a receiving individual of the same species. It is also called ‘ectohormone’.
Semiochemicals are those signalling chemicals that an orgalism can detect in its environment which may affect the organism’s behaviour or physiology. Phermones are those that act between members of the same species whereas allelochemics are those that act between species. The allelochemics may be allomones, which favour the emitter, or kairomones, which favour the receiver. Many allelochemics act both as an allomone and a kairomones.
Such chemicals are called synomones. Allomone is a substance produced by an organism that, on contact with an organism of another species, induces a response favourable to the individual that produced the substance e.g. the neotropical social wasp Mischocyttarus drewseni applies a secretion to the stem of its nest that repels foraging ants. Kairomones are such volatile compounds which evoke behavioural response adaptively favourable to the receiver.
Kairomones are secreted by host plant and host insects. The Kairomones secreted by host plant are used by the pests for their own benefit and the Kairomones secreted by the host insects are used by the natural enemies for their own benefit. The Kairomones secreted by host plant may be used as pest trap in the survey of the pest.
In the normal cases, the sex pheromone produced by the female acts as attractant and produced by male acts as aphrodiasiacs (i.e., to prepare female for copulation) The chemical nature of some sex pheromones have been discovered e.g., sex pheromone of Gypsy moth has been identified and synthesized as Cis-7, 8-epoxy-2 methyloctadecane.
Pheromones are used in two ways:
(a) Used as a luring agent.
(b) By breaking normal mating behaviour i.e., intersexual communication system of the pests.
Attractants and Repellants are also used in pest control. Geraniol and engenol to trap Japanese beetle (Popillia japonica) and Siglur to trap Mediterranean fruitfly are used as attractants. To repel cockroach N, N-diethyl-m-toluamide 2-hydroxy-n-octyl sulphide as repellant is used. Some chemicals like DTA [(4′ – dimethyltriazeno) acetianilide], Fentin acetate (fungicide) are used as antifeedants.
Natural Pyrethrin has the property of antifeedant. Antifeedants are such substances which inhibits from pest attack without killing or repelling the pests. These are also called feeding deterrents and rejectants. The pest dies slowly due to starvation. The crop or any material treated with such chemicals becomes antifeedant.