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IAA
Indol-3-ylacetic acid; a plant growth regulator.

I.C.A.O. standard
The standard atmosphere adopted by the International Civil Aviation

atmosphere
Organisation. Its chief specifications are: mean sea level (MSL) pressure 1013.25 mb; temperature 288.15 K (15°C); temperature lapse rate -6.5 K/km up to 11 km where the temperature is 216.65 K (-56.6°C) and with an isothermal lower atmosphere above 20 km.

Ick
Serious disease of freshwater fish, caused by ciliate protozoan Ichthyophthirius multifiliis.

Icosahedral
Many sided; a type of virus which does not possess an envelope and has a crystalline appearance; naked virus.

Icosahedron
A geometrical shape occurring in many virus particles, with 20 triangular faces and 12 corners.

Icterus
(Jaundice) Yellowing of the skin and other organs because of bile pigments in the blood.

Idiosoma
Posterior of the two basic parts of the body of a mite or tick, bearing the legs and most internal organs.

Illegitimate seed
Resulting from natural cross-pollination between plants or clones where the male parent cannot be ascertained.

Ileo-caecal (valve)
The valve formed by a projection of the mucous membrane at the junction of the ileum (last section of the small intestine) and the caecum (the large blind gut).

Ileum
The last part of the small intestine adjoining the large intestine.

Imago
The adult or reproductive stage of an insect.

Imagochrysalis
Quiescent stage between the nymph and adult in the life cycle of a chigger mite.

Imbibition
Absorption of water.

Immature
Young beef animal, generally a bull or castrate, which will have to grow out somewhat before finishing (cf. store).

Immature grains
Grains which are underdeveloped or not fully developed (sometimes referred to as unripe). Lacking in size and weight compared to a fully mature grain.

Immediate hypersensitivity
Biological manifestation of an antigen-antibody reaction in which the maximal response is reached in a few minutes or hours; intra-dermal injection of anitgen produces local swelling and redness with heavy infiltration of polymorphonuclear leukocytes; intravenous injection may produce anaphylactic shock and death.

Immigration
The movement of individuals into a population.

Imminent hazard pesticide
A situation in which the continued use of a pesticide during the time required for cancellation by the controlling authority would likely result in unreasonable adverse effects on the environment or to an endangered species.

Immune
Exempt from attack or infection by a given organism.

Immune cross-reaction
Binding of an antibody or cell receptor site with an antigen other than the one that would provide an exact 'fit', i.e. an antigen-antibody reaction in which the antigen is not the same one that stimulated the production of that antibody.

Immune response
The development of specifically altered reactivity following exposure to an antigen. This may take several forms, e.g. antibody production, cell-mediated immunity, immunological tolerance. Substances capable of inducing the response are called immunogens.

Immune system
The system in mammals which responds specifically to the presence of foreign antigens to aid in eliminating them from the body; provides acquired immunity.

Immunity
A type of resistance to attack; usually considered an acquired state in which an organism is capable of resisting a pest and thus preventing the development of a disease or damage. In animals it induces the production of antibodies. In plants, the ability to remain free from disease because of inherent structural or functional properties.

Immunisation
The process of increasing the resistance of the host. In plants, complete resistance to disease.

Immunoassay
A technique which detects proteins by using an antibody specific to that protein.

Immunochemistry
The study and use of antibodies as reagents and therapeutic substances, by virtue of their specific reaction with antigens.

Immunoconglutinin
Antibody against complexed antigen, antibody against that antigen, and complement.

Immunocytological methods
Procedures used to study cytopathological disorders in ultra-thin sections of virus diseased tissues, using labelled antibodies to diagnose the virus.

Immunodeficiency
Incomplete immune system; either antibody-mediated, cell-mediated immunity, or both may be abnormal.

Immunodiffusion
A serological procedure in which the antigen-antibody reaction is carried out be allowing the reactants to diffuse in gel.

Immunogenic
Refers to any substance that is anti-genic, i.e. stimulates production of antibody or cell-mediated immunity.

Immunogen, insect
It appears that an immune response in an insect is not the consequence of an antigen-antibody-globulin reaction but more likely the result of the production of some other principle in insect haemolymph; thus the term 'immunogen' may be used to replace 'antigen' when describing the stimulus to immune response by an insect; many insect immunogens may be conventional antigens (Cantwell, 1974).

Immunoglobulin
Any one of five classes of proteins in blood serum that function as antibodies; abbreviated IgM, IgG, IgA, IgD and IgE.

Immunological
Refers to the process of antibody formation and antigen-antibody reactions, whether or not immunity to infectious disease results.

Immunology
The study of acquired immunity in animals and man against infectious disease.

Immunopotentiation
An increase in the functional capacity of the immune response.

Immunosorbent electron microscopy (ISEM)
Techniques involving the visualisation of the antibody antigen reaction in the electron microscope. These include: Trapping: a procedure in which the EM grid is first coated with anti-serum (referred to as an antibody-coated grid [ACG]), which then attracts virus particles from a virus preparation placed on it. Decoration: in this technique virus particles are attached to the EM grid and then the anti-serum is added. Homologous antibodies will react with particles to coat or 'decorate' them.

Immunosuppression
Drug treatment which temporarily shuts off the immune system; often used during organ transplants to prevent tissue rejection.

Immunosurveillance
Recognition and elimination of cancer cells by killer T cells of the immune system. Malignant cells are destroyed before the formation of an overt tumour.

Immunotoxic
Harmful to the immune system.

Impact assessment
The process of measuring, modelling and monitoring a stressed ecosystem such as to predict significant change resulting from the stress or to detect such a change if it occurs.

Imperfect fungus
A fungus that is not known to produce sexual spores.

Imperfect reproduction
Reproducing without sexual processes.

Imperfect stage
Of fungi, the period of the life cycle other than that in which spores are formed as a result of a sexual process.

Imperfect state
The asexual period of a fungal life-cycle.

Impetigo
An infectious disease of the skin caused by staphylococci or streptococci.

Implementation
The process of coding, parameterising and calibrating a model.

Implementation document
A model document that keeps track of changes to model, parameters, processes and code involved in the implementation of the model.

Importance value
Sum of relative density, relative dominance and relative frequency for a species in the community; scale from 0 to 300; the larger the importance value, the more dominant a species in that particular community.

Inanition
Exhaustion from lack of nutrients.

Inbred
A normally cross-pollinated plant that has been self-fertilised.

Inbreeding depression
Loss of vigour and increased mortality in successive generations due to inbreeding.

Inbred line
The product of inbreeding; a line originating by self-pollination and selection.

Incidence (of a disease)
The number of new cases of a particular disease within a given period of time, in a population being studied.

Incitant
A factor that incites of activates occult pathogens.

Inclusion body
Virus induced structures that may occur in the cytoplasm or nucleus of infected plants.

Income effect
The change in a basket of goods selected by a consumer which takes place when the consumer's real income increase but relative prices remain the same.

Incompatible
Sprays which in a tank mix react with each other or the materials of which the equipment is built. Biologically incompatible sprays produce undesirable side effects on the crop when applied together. In plant pathology this term means that a pathogen is unable to form a parasitic relationship with a host plant usually since it has triggered the resistance responses of the host.

Incompatible materials
Materials who useful properties are adversely affected when mixed together.

Incompatibility
Failure to obtain fertilisation and seed formation after self-pollination, or within or between clones.

Incomplete dominance
Occurs when a dominant gene is only partially expressed in the phenotype of the heterozygote.

Incomplete metamorphosis
Similar to gradual metamorphosis but generally used to denote the growth changes of naiads.

Incorporate
To mix or blend a herbicide into the soil by mechanical means.

Incremental costing
A decision making technique used to calculate the change in total costs and revenues arising from a change in the level of activity.

Incremental expenditure
The additional expenditure incurred in pursuing a new project.

Incubation
Of a pathogen, its development, growth, and penetration of a plant prior to infection; or its activity within plant tissues subsequent to penetration and up to appearance of symptoms, signs of disease or both.

Incubation period
The period of time elapsing between entrance or introduction of micro-organisms in the host and the development of symptoms and signs of an infectious disease.

Independent variable
A non-random variable related to the response in a regression equation. One or more independent variables may be functionally related to the dependent variable. They are used in the regression equation to predict or estimate the value of the dependent variable.

Indeterminate
A plant that flowers over a long period; ripe seeds, blossoms and vegetative shoots may be present on the plant at the same time. The terminal flowers tend to be the last to open, so that the floral axis may be prolonged indefinitely by a terminal bud.

Indexing
Process of determining the presence of disease in a plant by transferring inoculum from the plant to another in which diagnostic symptoms develop. The second plant is termed a 'test' or an 'indicator plant'.

Index of prevalence
Proportion of plant stands affected by disease or infestation in defined area.

Index of similarity
Ratio of the number of species found in common in two communities to the total number of species that are present in both.

Indexing
Determining virus infections of the host by transmission tests on virus indicators.

Index number
The quantity that shows the change over time from some base period to a reference period of a variable process that is not directly observable in practice.

Indicator
Marker. A plant that reacts to certain viruses or environmental factors with production of specific symptoms and is used for detection and identification of these factors.

Indicator organism
An organism associated with the intestinal tract whose presence in water indicates faecal contamination.

Indicator plant
One that reacts to certain viruses or environmental factors with specific symptoms and is used for identification of the viruses or the environmental factor.

Indicator, virus
Plant used to demonstrate symptoms of specific virus infection.

Indifference analysis
A method of modelling consumer behaviour.

Indifferent species
Species occurring in many different communities; not good species for community classification.

Indirect costs
Sometimes these are called overheads; they comprise all costs of R & D which are allocable to the general R & D function, but not to any particular project.

Indirect hyperparasite
A secondary parasitoid that locates and oviposits its egg in the body of an unparasitised, non-parasitic host the egg usually remaining undeveloped until the non-parasitic host is subsequently parasitised by a primary parasitoid which then serves as host for the secondary.

Indirect loss
Loss caused by a lowering of quality leading to rejection as food. This type of loss may be locally defined and related to custom (see grading).

Indirect selection
Selection for a trait other than the one desired to improve, based upon the existence of a genetic correlation between the two traits.

Induced enzyme
An enzyme subject to induction.

Inducible enzyme
An enzyme whose synthesis does not occur unless a specific chemical, called an inducer, is present; the inducer is often the substrate of that enzyme.

Induction
The process by which an enzyme is synthesised in response to the presence of an external substance, the inducer. Also, the activation of an occult pathogen, leading to progressive infection and disease; in particular, the provoked transformation of a provirus into a virulent (cytocidal) virus.

Induration
The process of hardening of a tissue.

Inert
A material having no biological action.

Inert ingredient
Any substance in a pesticide product that has no pesticidal action.

Infaunate
To introduce a commensal or mutualistic micro-fauna into an organism that is capable of serving as a host.

Infect
Of a parasite or pathogen, to enter and grow, or to replicate, within plant tissues. If the association is non-injurious, the relationship is simply parasitic; if it is injurious, the relationship is pathogenic as well as parasitic.

Infection
The introduction or entry of a parasite or pathogenic micro-organism into a susceptible host, resulting in the presence of that organism within the body of the host, whether or not this causes detectable pathologic effects (or overt disease).

Infection chain or cycle
The never-ending sequence of infection, colonisation, sporulation, dispersal and again, infection.

Infection court
The initial site of contact between a pathogen and the surface of the host. The place in or on the susceptible plant where infection may be initiated.

Infection gradient
Change in incidence of disease with distance from source of infection.

Infection unit
The mycelial structure that originates from a dispersal unit, can be recognised visually, counted, and/or measured up until the point that it, in time, gives rise to new dispersal units.

Infection peg
A slender structure formed by the deposition of substances such as lignin around a thin fungal hypha penetrating a host cell.

Infection stage
The period during which the disease producing organisms causes symptoms of disease to appear in a plant.

Infection structures
A term used to describe the germ tube, appressorium, infection peg, substomal vesicle and infection hyphae of rust fungi.

Infection thread
The specialised hypha of a pathogenic fungus that invades tissue of the susceptible plant. Also, the primary colonisation and inward movement of Rhizobium cells within the root hair of a leguminous plant.

Infection type
The physical appearance of a parasitic lesion on a host plant. These are often classified as high or low and there may be a numerical system to enable further distinctions to be made.

Infectious
Refers to a pathogen that can be transmitted from one suscept to another by an external agent; also refers to any disease whose pathogen can be so transmitted.

Infectious disease
Disease caused by the actions of a living organism.

Infectious period
The period of sporulation or production of dispersal units.

Infective
An organism or part thereof capable of establishing a pathogenic relationship with a host i.e. capable of transmitting inoculum.

Infective phase
The last phase of the developmental cycle of a virus, in which the virus acquires infectivity through the assembling of the genome and proteins during the maturation phase.

Infectivity assay
A bioassay using mechanical sap-transmission to quantitatively determine the amount of infectious virus.

Inferential statistics
That branch of statistics dealing with procedures used to make inferences about a population from information contained in a sample.

Infest
With insects to occupy and cause damage; referring to soil, contaminate by fungi, eelworms or insects To be present in numbers. To introduce a pathogen into the environment of a host. Infestation does not imply disease and is not to be confused with infection.

Infestation
Presence of pests on the plant crops.

Infested
Containing great numbers of insects, mites, nematodes, etc. as applied to an area or field. Also applied to a plant surface or soil contaminated with bacteria, fungi, etc.

Inflammable
Deprecated symbol for flammable.

Inflammation
A response of host tissues to injury, microbial infection or presence of foreign particles, characterised by swelling, redness, pain and accumulation of phagocytes at the site.

Inflation
An increase in the supply of money in relation to the goods and services available, and, in consequence, a decline in its value.

Inflorescence
The flowering portion of a plant. The arrangement and mode of development of the flowers on the floral axis of a plant.

Information agreements
Agreements between firms to share information on issues like price, in order to establish a tacit form of collusion.

Informational macro-molecule
A macro-molecule that plays a role in the transfer or expression of genetic information.

Information flow
Where a component influences another component without the physical transfer of material.

Infraciliature
All cilia basal bodies and their associated fibrils in a ciliate protozoan.

Infrapopulation of parasites
All individuals of a single parasite species in one host.

Infra-red radiation
Electromagnetic radiation in the approximate wavelength range from about 0.7 to 1000 µm, 53% of the total solar radiation intensity is contained within this range of wavelengths, the amount of wavelengths greater than 4 µm being very small. In meteorology, the term is often used loosely as an alternative for long-wave radiation.

Infra-red spectrophotometry
A widely used technique employed in the identification of organic compounds by passing different wave lengths of the infra-red region of light through solutions in suitable solvents.

Infusoriform larva
Ciliated larva produced by an infusorigen within a dicyemid mesozoan.

Infusorigen
Mass of reproductive cells within a rhombogen.

Ingest
To eat or swallow.

Ingredient, active
An ingredient in a pesticide or its formulation which is not pesticidally active, i.e. water, emulsifying agent, diluent, carrier etc.

Ingredient statement
That portion of the label on a pesticide container that gives the name and amount of each active ingredient and the total amount of inert ingredients in the formulation.

Ingress
The act, by a plant pathogen, of gaining entrance into the tissues of a susceptible plant.

Inhalation toxicity
Toxicity of a material to man or animals when breathed into the lungs.

Inherited disease
A disease, abnormal characters or qualities inherited and transmitted from parent to offspring.

Inhibit
To hold in check or stop, as to inhibit or check seed germination or plant growth with chemicals.

Initial conditions
The values of the state variables at the start of a simulation.

Initiator
An agent which starts the process of tumour formation, usually by action on the genetic material.

Injector (gun)
A device for ejecting a pesticide below the soil surface, or into the transport system of a tree.

Injector pump
See pump iv.

Injury
Damage of a plant by an animal, physical or chemical agent which impairs plant growth, function and/or appearance but does not necessarily result in loss yield and/or quality.

Innate capacity for increase (rm)
Measure of the rate of increase of a population under controlled conditions.

Innate resistance
The non-specific defences already present in the body which are stimulated by infection or trauma, e.g. phagocytosis or inflammation.

Inoculate
To introduce dispersal units on or into a host for the purpose of producing infection of testing susceptibility to infection e.g. a pathogen in contact with a host plant.

Inoculation
Applying nodule bacteria on legume seeds just before planting them. To transfer inoculum to or into an infection court.

Inoculation feeding period
The length of time a vector feeds on a test plant during transmission experiments.

Inoculation stage
The period during which inoculum is being transferred from its source to the infection court.

Inoculation threshold period
The minimum feeding period a vector needs on a test plant to transmit a virus.

Inoculative releases
The repeated release of relatively small numbers of a natural enemy for purposes of building-up a population over several generations.

Inoculum
That portion of a pathogen which is transferred to a host and is capable of infecting it. It may consist of spores, bacteria, mycelial fragments or virus particles.

Inoculum density
The number of infective units (propagules) in a given volume or area.

Inorganic compound
A compound which does not contain carbon atoms (the only exception being carbon dioxide CO2).

Input
Any resource used in production, e.g. land, labour or capital.

Inquiline
An organism that habitually lives on or within the body of another, or in its nest or abode, without benefit or damage to either.

Insect growth regulator
Chemical substance which disrupts the action of insect hormones that control moulting, development from pupa to adult and other processes (Watson, Moore & Ware, 1976).

Insect pest management
The practical manipulation of insect (or mite) pest populations using any or all control methods in a sound ecological manner (Watson, Moore & Ware, 1976).

Insecticide
The term 'insecticide' includes all preparations intended for preventing, destroying, repelling or mitigating any member of the class Insecta or allied classes in the phylum Arthropoda.

Insectivorous
Feeding on insects.

Insertion
A genetic phenomenon in which a piece of DNA is inserted into the middle of a gene.

Insertional activation
Loss of function as a result of integration of a DNA vector into a site conferring a property such as antibiotic resistance.

In situ
In the original situation. In place; generally used in micro-biology to refer to the study of micro-organisms in their natural environments, such as soil, water, the animal body.

Insolation
Generally, the effect of the sun's rays on the animal exposed directly to the sun, that produces much higher temperatures than the ambient temperature, especially at high tropical altitudes. More specifically (i) The intensity at a specific time, or the amount in a specific period, of direct solar incident on a unit area of a horizontal surface on or above the earth's surface. (ii) The intensity at a specific time, or the amount in a specific period, of total (direct and diffuse) radiation incident on a unit area of a specified surface of arbitrary slope and aspect.

Instant
One of the important designations of time; an infinitely short period, sometimes indicated as 'moment'.

Instar
A stage in the development of a larva between two moults. The first instar being the stage between hatching and the first moult.

Intangible assets
Assets of a non-physical nature including goodwill, patents, trade marks and royalty agreements.

Integrated control
Control measures incorporating both biological and chemical treatments (Marsh, 1969).

Integrated use of both biological and e.g. chemical methods of controlling pests or weeds (Spedding, 1975).

The integration of the activities of natural enemies of pest organisms with cultural, physical and/or chemical control measures (Cantwell, 1974).

The integration of the chemical and biological control methods (Whitaker, 1983; Watson, Moore & Ware, 1976).

The manipulation of pest populations using any or all control methods in a sound ecological manner (Stiling, 1985).

A strategy that utilises knowledge, monitoring, action criteria, materials and methods in concert with natural mortality factors, to manage pest populations (van den Bosch, 1980).

The continuous application of a balanced range of disease control measures (Parry, 1990).

An ecologicallly based pest population management system that uses all suitable techniques to reduce or so manipulate the pest populations that it is prevented from causing economically unacceptable injury to the crop.

The control of harmful organisms which employs all available methods consistent with economic, ecological and toxicological requirements (Chiarappa, 1980).

Integrated pest management
The planned use of more than one method to regulate the level of harmful organisms once their actual and projected intensity and effect is known (Chiarappa, 1980).

A pest management system that in the context of the associated environment and the population dynamics of the pest species, utilises all suitable techniques and methods in as compatible manner as possible and maintains the pest population levels below those causing economic injury (Smith and Reynolds, 1966).

A management system that uses all suitable techniques and methods in as compatible a manner as possible to maintain pest populations at levels below those causing economic injury (Whittaker, 1983).

Integration
The process by which a DNA molecule becomes incorporated into the genome.

Integuments
The coats or walls of an ovule or the epidermis and cuticle of an insect.

Intensity/loss relationship
The relation between pest and disease attack and depression in yield.

Interaction
A measure of the extent to which the effect of one factor varies as the levels of the other factors are changed.

Interaction diagram
Plots used to show the form of the interaction between two variables in their effect on some quantity of interest.

Interallelic
Expression governed by alleles of more than one pair.

Intercalary
Formed along and within the mycelium - not at the hyphal tips.

Intercalary meristem
Meristematic tissue derived from the apical meristem and interposed between tissues that are more mature. Often found above the nodes in immature grass stems.

Intercellular
Between cells.

Intercostal (muscle)
The muscles connecting each rib with its neighbouring ribs.

Intercropping
The growing of two crops simultaneously in the same field.

Interest
The cost of 'hiring' money from a lender.

Interest (flat)
A way of calculating interest in hire purchase and lease agreements. The interest is charged, over the period of the loan, on the amount originally borrowed, even though some of the loan has been repaid. It is nearly twice as expensive as simple interest.

Interest (simple)
The hiring charge of borrowed money, calculated on the amount owed, at any one time.

Interfacial reaction micro-encapsulation
Micro-encapsulates are formed by emulsifying or dispersing the core material in an immiscible continuous phase and then an interfacial polymerisation reaction is caused to take place at the surface of the core particles. These are basically three methods: interfacial addition, condensation and in situ condensation.

Interference
The interference of one virus with the multiplication or the disease-producing capabilities of a second, unrelated virus.

Interferon
A naturally occurring anti-viral agent, produced as a result of virus infection or the presence of some nucleic acids, that interferes with virus replication.

Intergeneric hybrids
Hybrids derived from crossing two species, each of a different genus. A viable example is triticale, a hybrid of wheat of the genus Triticum and rye of the genus Secale. The more distant the relation between the two genera, the greater the difficulty of intergeneric hybridisation. Many intergeneric hybrids are infertile.

Intermediate host
Host in which a parasite develops to some extent but not to sexual maturity.

Intermittent parasite
Temporary parasite.

Intermediate variable
Variables that are used to compute process rates and are often of interest to the modeler, e.g. photosynthesis rate.

International Unit IU
An arbitrarily-set basis for comparing the efficacy of insect-pathogenic Bacillus thuringiensis preparations. An International Unit is one thousandth of the amount of insecticidal activity contained in one milligram of a preparation of the primary standard E-61 strain of B. thuringiensis, as measured by bioassay against certain lepidopterous larvae (i.e. comparative LD50). A formulation of B. thuringiensis with a potency of 1,000 IU/mg is, therefore, equal to the international standard. A secondary reference standard B. thuringiensis strain (HD-1-S-1971) is in use in the USA, and has been assigned a potency of 18,000 IU/mg against the cabbage looper, Trichoplusia ni (Hübner).

Internode
The portion of the stem between two nodes or joints.

Interplanting
The interplanting of one crop within another for the purpose of trapping pest insects.

Interplot interference
An interaction between plots in field experiments, arising whenever particular treatments affect plots other than those to which the treatments were applied. The principal cause of representational errors e.g. increased levels of infestation on resistant test plants due to their proximity to susceptible plants.

Intersection
If A and B are two events in a sample space S, the intersection of A and B is the event composed of all sample points that are in both A and B and is denoted by AB.

Interspecific competition
Competition between members of different species.

Interstitial
Pertaining to the supporting tissue lying among the functional tissue of an organ.

Intertilled
A crop planted in rows and cultivated between the rows.

Interveinal
Between the structural vessels or veins.

Intoxication
An adverse effect due to the intake of or exposure to any substance i.e. poisoning.

Intra-allelic
Expression governed by one of a single pair of alleles.

Intra-cellular
Within or through the cells.

Intra-hemocoelic
Within the hemocoel or perivisceral cavity of an invertebrate; as in 'intra-hemocoelic injection'.

Intra-lecithal cleavage
Cleavage in which the nuclei undergo several divisions within the yolk mass without concurrent cytokinesis; common in arthropods.

Intra-muscular
Within the muscle e.g. in pesticide toxicological tests the pesticide is injected in the muscle.

Intra-peritoneal
Injected in the viscera but not into the organs.

Intravenous
A method of introduction of a substance directly into the vein of a test animal.

Intrinsic environment
Environmental variables that are modified by the biota such as sunlight through a forest canopy.

Introgression
The entry or introduction of a gene from one gene complex into another.

Intron
A eucaryotic DNA segment that does not code for protein but may interrupt segments which do encode protein. Contrast with Exons, the coding sequences.

Intumescence
Hyperplastic symptom characterised by blister-like swelling (due to water excess) on the surfaces of plant organs.

Inundative release
Release of large numbers of natural enemies to effect immediate high mortality in the pest population.

Invaginate
The infolding of a portion of an organ within the remainder.

Invagination
Retraction, under force of pressure, of an outer surface toward the inside.

Invasion
Spread of a pathogen i.e. micro-organisms through tissues of a diseased plant.

Invasion area
In locusts the area colonised by swarms during an outbreak; the invasion area cannot support permanent populations of locusts.

Invasiveness
Degree to which an organism is able to spread through the body from a focus of infection.

Inverse density- dependent mortality
Mortality inflicted on the members of a population, the magnitude of which decreases as the density of the population increases and vice versa.

Inverse matrix
For square matrices, the matrix such that when pre-multiplied or post-multiplied by the original matrix the result is the identity matrix I.

Inversion
In meteorology, describes the state of the lower atmosphere when the temperature is lowest near the ground. Usually occur at night. The lower atmosphere is non-turbulent in inversion in contrast to its turbulent state under the opposite (lapse) condition when the ground is warmed by solar radiation.

Inversion layer
An atmospheric layer in which there is an inversion of temperature.

Invertebrates
A member of the division of the animal kingdom called the invertebrate, the chief characteristic of which is that they do not possess a spinal column, such as insects, slugs, spiders etc.

Invert emulsion
An emulsion in which the water is dispersed in oil rather than oil in water. Oil forms the continuous phase with the water dispersed therein; usually a thick mixture usually results.

Investment appraisal
An evaluation of the profitability of a farm development plan.

Investment centre
A type of responsibility centre where the manager is responsible for revenues, costs, profit and investment culminating in either a residual profit or return on capital objective.

in vitro
Literally 'in glass': refers to experiments carried out in an artificial laboratory environment usually on micro-organisms in isolation of their natural hosts or other living organisms. Also used in digestibility estimates made in laboratory with rumen liquor. Contrast with in vivo.

in vivo
Refers to an experiment on living organisms living in their natural environment within a living organism. Contrast with in vitro.

Iodinophilous vacuole
Vacuole within a protozoan that stains readily with iodine.

Ion
Electrically charged element, group of elements or particle. Many of the salts in the soil solution exist as ions.

Ionisable
A chemical which is able to become charged with either positive or negative ionic charge.

Ionisation
Dissociation of substances in water to form atoms or groups of atoms carrying an electric charge.

Iridescent virus disease
A disease of Diptera, Lepidoptera, and Coleoptera, caused by large icosahedral viruses.

Irrelevant costs
Costs which remain unaffected by the decision under review and can therefore be ignored.

Irritability
Responsiveness to change in the physical or biological environment; a property of all living things.

Isoelectric point
The pH at which a virus particle has a zero net charge.

Isoelectric precipitation
The precipitation from suspension of a virus or a protein when the pH is at the isoelectric point, i.e. when there is no positive or negative surface charge on the virus or protein.

Isoenzyme
One or more forms of an enzyme having catalytic properties ascribed to that enzyme.

Isogametes
Outwardly similar male and female gametes.

Isogamy
The condition in which gametes are morphologically similar, as in the members of the subclass Zygomycetes of the class Phycomycetes.

Isolate
A single spore or culture and the subcultures derived from it. Also used to indicate collections of a pathogen made at different times.

Isolation
The procedure by which a pathogen is separated from its host and its culture on a nutrient medium. Also, confinement of a hospital patient to reduce the spread of infectious disease either from, or to other patients.

Isomer
Briefly, two compounds are said to be isomeric if they are composed of the same elements in the same proportion by weight but have different chemical and physical properties.

Isometric
Used to describe virus particles that are approximately spherical in shape.

Isoprenoid
Organic chemical, of or related to the hydrocarbon isoprene C5H8.

Isoquant
A curve showing all the different quantities of capital and labour which may be used to produce a given level of output.

Isotherm
Line drawn on a map or chart connecting places with the same temperature at a particular time or for a certain period.

Isozymes or isoenzymes
Enzymes that have identical catalytic function but different structures, differing usually in regulatory control. Typically this subtle difference in molecular structure allows each isozyme to be separated e.g. by electrophoresis.