[A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Y] [Z]
Ear
The heavy spike of spike-like inflorescence, such as the ear of wheat.
EC50
The median effective concentration (ppm or ppb) of the toxicant in
the environment (usually water) that produces a designated effect in 50%
of the test organisms exposed.
EC50; EC90
1. The concentrations at which 50 or 90% of a population reacts.
2. The concentration at which the reaction of an organism is 50% or
90% less than the control value.
Ecchymotic
Pertaining to ecchymosis.
Ecchymosis
An effusion of blood into the tissues causing irregular patches visible
on the surface of an organ or tissue.
Ecdysis
Moulting or discarding of in-expansible portions of cuticle in arthropods,
after which there is an increase in size of the individual's body before
the newly secreted cuticle hardens.
Ecdysone
Hormone secreted by insects that is essential to the process of moulting.
Ecesis (= Oikesis)
The establishment of an organism in a new habitat; accidental dispersal
and establishment in a new area.
Eclipsed antigen
Antigen borne by the parasite that is common to both the host and the
parasite but which genetically is of parasite origin.
Eclipse period
In the developmental cycle of viruses, a phase or period, occurring
immediately after infection (i.e. immediately after a virus enters the
host cell), in which infective particles cannot be detected.
Eclosion
The process of hatching from the egg.
Eco-climate
Climate within a plant community, e.g. crop.
Ecological longevity
Average length of life of individuals of a population under stated
conditions.
Ecologic
Pertaining to the relationship between an organism or organisms and
features of the environment.
Ecology
Derived from the Greek oikos, 'house or place to live', the science
dealing with living organisms and their relation to the environment.
(Applied to plant pathology) The study that deals with the effect
of environmental factors, such as soil, climate and culture etc. on the
occurrence, severity and distribution of plant diseases or plant pathogens.
Econometrics
The application of statistical methods to the estimation of economic
models.
Econometric model
An econometric model is a probabilistic model consisting of a system
of one or more equations that describe the relationship among a number
of economic and time series variables.
Economic damage
The amount of injury which will justify the cost of artificial control
measures.
Economic injury level
The degree of crop damage or pest density at which economic losses
become significant.
The lowest population density that will cause economic damage.
Economic pest
A pest that can cause a crop loss of between 5-10%.
Economic poison
The term 'economic poison' means any substance or mixture of substances
intended for preventing, destroying, repelling or mitigating any insects,
rodents, nematodes, fungi or weeds or any of the other forms of life declared
to be pests; and any substance or mixture of substances intended for use
as a plant regulator, defoliant or desiccant.
Economic threshold
The pest population level at which control measures should be started
to prevent the pest population from reaching economic-injury level (Hill,
1983).
The density of pest population at which a control action becomes profitable
(Stern, 1966) (see action threshold).
Economies of scale
Reductions in cost which arise from the utilisation of larger sets
of machinery and equipment.
Economies of scope
Reductions in cost which arise from producing a number of different
products together.
Ecosystems
The interacting system of all the biotic community and its abiotic
environment.
Ecotone
Transition zone between two diverse communities (e.g. the tundra-boreal
forest ecotone).
Eco-toxicology
The study of toxic effects of chemical and physical agents in living
organisms, especially on populations and communities within defined ecosystems;
it includes transfer pathways of these agents and their interaction with
the environment.
Eco-type
Subspecies of race that is especially adapted to a particular set of
environmental conditions. Individuals are infertile with each other and
members of other eco-types of the same species.
Ecto-
A Greek-derived prefix meaning external. Here used only to qualify
parasite, to distinguish, e.g. fleas and ticks from endo- (internal) parasites
such as disease-producing micro-organisms.
Ectocardial
Pertaining to the outer surface of the heart.
Ectocommensal
Commensal symbiont that lives on the outer surface of its host.
Ectodesmata
Strands of protoplasm linking cells.
Ectoparasite
An organism that lives parasitically on the outside of it host.
Insects which live on the skin of cattle, e.g. ticks, lice, fleas.
Ectopic
Infection in a location other than normal or expected.
Ectosymbiosis
Symbiosis in which one member (micro-symbiote) develops on the outside
of the other member.
Ectotrophic
Refers to a mycorrhiza in which the mycelium forms an external covering
on the root (e.g. in pine).
ED50
The median effective dose of a pesticide, expressed as mg/kg of body
weight, which produces a designated effect in 50% of the test organism
exposed.
Edaphic
Of or pertaining to soil or, more generally, substrate, especially
as it affects living organisms.
Edema
Accumulation of more than normal amounts of tissue fluid or lymph in
the intercellular spaces, resulting in localised swelling of the area.
Edible
Not toxic; nutritious, as a worm to a chicken, a chicken to a man,
and a man to a worm.
Eelworms
Nemas, nematodes.
Effective concentration
EC Refers to a concentration of a chemical substance effective in
producing some specific result such as death, paralysis, increase in oxygen
consumption etc.
Effectiveness
Pertaining to the degree to which a dispersal unit or population of
dispersal units leads to establishment of new infections.
Effects matrix
A matrix having coefficients that represent both the sub-lethal and
lethal effects of toxicants on ecosystem biota.
Efficacy
Capacity to produce the desired effect.
Efficiency
A ratio of output (or performance or success) to the input(s) (or costs)
involved, over a specified time and in a specified context.
Efficiency of a pest control measure
The more or less fixed reduction of a pest population regardless of
the number of pests involved.
Effect
A biological change in an organism, organ or tissue.
Efficiency ratio
Used in standard costing to measure efficiency by expressing the standard
hours equivalent of the work produced as a percentage of the actual hours
taken.
Egestion
The process of passing indigestible material out of the gut. Also
termed defecation.
Egg
A female gamete. In nematodes, the first stage of the life cycle containing
a zygote or a larva.
Egg cell
The female germ cell. On being fertilised by the male sperm it develops
into the embryo.
Eigenanalysis
The finding of eigenvalues and eigenvectors of a square matrix.
Eigenvalues
Coefficients associated with a matrix A that satisfy the equation |A
- I| = 0. Used in the solution to linear compartment models and Leslie
matrices.
Eigenvectors
Vectors vi associated with eigenvalues i of a matrix A satisfying
the relationship Avi = ivi.
Elateriform larva
A larva resembling a wire-worm with a slender body, heavily sclerotinised,
with short thoracic legs and only a few body bristles.
Electron acceptor
A substance that accepts electrons during an oxidation-reduction reaction.
An electron acceptor is an oxidant.
Electron donor
A compound that donates electrons in an oxidation-reduction reaction.
An electron donor is a reductant.
Electron-transport phosphorylation
Synthesis of ATP involving a membrane-associated electron transport
chain and the creation of a proton-motive force. Previously termed oxidative
phosphorylation.
Electrophoresis
A technique used to separate chemical substances according to the electrical
charge on their molecules which migrate in response to the application
of an electric field.
Electrophoretic mobility
The rate of movement of virus per unit potential gradient. Mobility
may be towards the cathode or the anode depending on whether the virus
has a net positive or negative charge at the pH used.
Electrostatic application
A pesticide spray application technique by which droplets are given
an electrostatic charge.
Electrotaxis
A response in which an electromotive force constitutes the energy of
activation.
Elfinwood
(Krummholz) scrubby, stunted growth form of trees, often forming a
characteristic zone at the limit of tree growth in mountains.
Elicitor
A physical, chemical or biological stimulus that triggers defence responses
in plants.
Elimination (in metabolism)
The expelling of a substance or other material from the body (or a
defined part thereof), usually be a process of extrusion or exclusion,
but sometimes through metabolic transformation.
ELISA
Enzyme linked immunosorbant assay; a very sensitive diagnostic test
that employs antibodies linked to an enzyme whose activity can be determined
for the quantitative determination of the antigen which reacts with that
antibody.
Elytra
The hard upper wings of beetles.
Elytron/femur ratio (E/F)
Ratio of the length of the elytron (outer wing) of locust to the length
of the femur (part of hind leg); used to determine morphological phase
status of locusts.
Emaciated
Reduced in flesh; thin.
Emasculate
To remove the anthers (male organs) from a bud or flower before the
pollen is shed.
Embolism
In plant pathology a term used to describe the disruption of water
conduction, usually by an air-lock.
Embryo
An organism in its earliest stage of development usually surrounded
by protective tissue e.g. a plant still enclosed in the seed which arises
from the zygote.
Embryo/feto-toxicity
Any toxic effect on the developing foetus resulting from prenatal exposure,
including structural or functional abnormalities or post-natal manifestation
of these.
Embryonated
Containing an embryo, i.e. the early developing stage of life after
fertilisation of the egg by the sperm.
Embryogenesis
The simultaneous initiation of root and shoot meristems in component
cells so that bipolar structures develop into embryos and later into whole
plants.
Embryonic callus
Callus cultures that under suitable conditions are capable of producing
embryos (i.e. young plants). Conversely callus cultures that have lost
this capability are termed 'non-embryonic'.
Embryo rescue
When cross-pollination occurs between genetically widely different
plants, the resulting embryo may be aborted because of parental mutual
incompatibility. Such embryos may be excised and grown on a congenial
medium such as nutrient agar. This process is called embryo rescue.
Emergence
(i) The adult insect leaving the pupal case.
(ii) Germination of a seed and the appearance of the shoot.
The time when the first leaves of the crop plant come through the ground.
Emigration
The movement of individuals out of a population.
Emission standard
A quantitative limit on the emission or discharge of a potentially
toxic substance from a particular source. The simplest system is uniform
emission standard where the same limit is placed on all emissions of a
particular contaminant.
Empirical distribution
The cumulative distribution function of a sample of size n, denoted
Fn(x). It is 1/n x {the number of values in the sample less than or equal
to x}.
Emphysema
The presence of air in the alveolar tissue of the lungs. It is caused
when damage to the alveoli allows air to penetrate the interstitial tissue
which then inflates.
Emulsifiable concentrate (= Miscible oil)
A liquid pesticide formulation that when added to water spontaneously disperses as fine droplets to form a stable emulsion. The more water
that is added the thinner the emulsion becomes.
Emulsifiable liquid
A liquid that will form an emulsion when it is mixed with water.
Emulsifier
Surfactant used to stabilise suspensions of one liquid in another,
e.g. oil based pesticide formulations in water or water based pesticide
formulations in oil.
Emulsion
Very fine droplets of one liquid dispersed in another, e.g. oil in
water.
Enation
An abnormal outgrowth (often on the leaf) often induced by virus infection,
caused by an increase in cell numbers (hyperplasia) e.g. gall formation
Encapsidation
The enclosure of a virus's nucleic acid genome with a protein shell.
Encapsulation (or encapsulated formulation)
Or micro-encapsulation: the encapsulation of a pesticide in a non-volatile
envelope of gelatine, polyvinyl or other material, usually of minute size,
for controlled release of the chemical to extend the period of diffusion.
Encephalitic syndrome
The syndrome exhibited by an animal due to a disease condition of the
brain.
Encephalitis
Inflammation of the brain.
Encyst
To form a cyst.
Encysted
Surrounded by a hard shell (cyst).
Endangered species
A species of animal or plant threatened with extinction.
Endemic
Refers to an organism restricted to a particular area, that is constantly
present in low numbers in a population.
Endergonic
A chemical reaction requiring input of energy to proceed.
Endite
Medial process from the protopod.
Endo-
Opposite of ecto-
Endocommensal
Commensal symbiont that lives inside its host.
Endocytosis
Ingestion of particulate matter, fluid or virus by phagocytosis or
pinocytosis; i.e., bringing material into a cell by invagination of its
surface membrane, then pinching off the invaginated portion as a vacule.
Endodermis
A layer of cells with thick walls and no intercellular spaces that
surrounds the vascular tissues of the roots.
Endodyogeny
Same as endopolyogeny except that only two daughter cells are formed.
Endogenous
Arising from within the generating structure (e.g. endoconidia of Thielaviopsis
basicola).
Endolytic insecticides
Systemic insecticides that remain in their original form until decomposed
by the biological system in which they are taken up.
Endometatoxic insecticides
Systemic insecticides which are transformed or metabolised by the biological
system in which they are taken up to secondary toxicants.
Endonuclease
Nucleases are enzymes that break down nucleic acids into strands of
DNA. 'Endo' or inside nucleases act at points along the strand and thus
break DNA into short pieces. Endonucleases recognise a particular base
sequence in DNA and cut the DNA. Some endonucleases cut the DNA at a specific
point while others randomly split the DNA sequences. Specific endonucleases
are used by genetic engineers who excise strands of DNA coded for a desirable
genetic character. Endonucleases are classed as 'Restriction enzymes'
since they are employed e.g., by bacteria to restrict infection by viruses
(bacteriophages). The bacterial restriction enzyme attacks the DNA of
the infecting organisms.
Endoparasite
Parasites which live inside the host and feeds internally on its tissues,
e.g. tapeworm, liver fluke, lung-worm.
Endoplasmic reticulum
A complex pattern of internal membranes that permeates the cytoplasmic
matrix of eucaryotic cells.
Endopod
(Endopodite) Medial branch of a biramous appendage.
Endopolyogeny
Formation of daughter cells, each surrounded by its own membrane, while
still in the mother cell.
Endopterygote
Condition of internal wing bud development in an insect; also, an insect
secondarily wingless but derived from such an ancestor; associated with
holometabolous insects.
Endo-skeleton
The bony and cartilaginous structure which is inside the body.
Endosome
Nucleous-like organelle that does not disappear during mitosis.
Endosperm
The starchy or oily nutritive material that surrounds the embryo in
some seeds (sometimes referred to as albumen); it is triploid, having arisen
from the triple fusion of a sperm nucleus and the two polar nuclei of the
embryo sac.
Endospore
A structure produced inside some bacteria, highly resistant to heat
and chemicals; can germinate to form a new cell.
Endosymbiosis
Symbiosis in which one member (micro-symbiote) lives within the other.
The hypothesis that mitochondria and chloroplasts are the descendants
of ancient procaryotic organisms.
Endothermic reaction
A chemical reaction that requires input of energy to proceed.
Endotoxins
Substances produced by micro-organisms which are not secreted into
the surrounding medium but are confined within the microbial cell; they
are released after auto-lysis.
A toxin not released from the cell; bound to the cell surface or intra-cellular.
Endothelial cells
The flat thin cells which line blood and lymph vessels and the body
cavities.
Endotrophic
Refers to a mycorrhiza in which the mycelium grows within the cortical
cells of the root (e.g. in orchids).
Energetics
The study of the energy transferred to or expended in life processes.
Energy flow
The rate of energy transfer between elements of an ecological system.
Engel curve
A curve showing the relationship between a household's income and its
consumption of a commodity.
Enphytotic
The sudden and destructive development of a plant disease, usually
over large but restricted areas.
Enrichment culture method
A technique for isolating organisms from nature using media and growth
conditions highly selective for a particular type.
Ensilage
Silage.
Ensiling
Curing succulent animal feed in the silo.
Entanglement
The process of being tangled in net fragments or other flotsam.
Enteric
Intestinal
Enterotoxin
A toxin affecting the intestine.
Enterovirus
A virus which causes infections of the gastrointestinal tract; sometimes
this term is used to indicate a group of picornaviruses which cause such
infections as polio and infectious hepatitis.
Enterprise
The production of a particular commodity or group of related commodities.
Entner-Doudoroff pathway
A reaction sequence used by some bacteria to catabolise glucose.
Entomophagous
An animal (or plant) which feeds on insects.
Entomophagy
The consumption of insects by other animals.
Entomophilic
Used to cover the associations between insects and plant micro-organisms,
insects and protozoa, and insects and nematodes; meaning 'insect loving'.
Entomophilous
Insect-pollinated.
Entomophyte/entophyte
A plant living within or on the body of an insect.
Entomophytic
Refers to almost any relationship between plant micro-organisms (bacteria
and fungi) and insects.
Entrainment
The process of being captured in cooling water of a power plant. This
usually applied to small organisms such as fish larvae and zooplankton.
Entropy
The degree of randomness or disorder in a system.
Envelope
The outermost layers of a cell or the membrane of a virus.
Enveloped virus
Plant viruses of the reovirus and rhabdovirus groups which have an
outer lipid-protein membrane surrounding the protein shell of the virus.
Environment
The external conditions (biotic and abiotic) that may act on soils
or organisms to influence their development, which includes sunlight, temperature,
moisture and other organisms.
Environmental biotypes
Biotypes distinguished by their degree of sensitivity to environmental
factors (e.g. moisture, temperature) rather that to host resistance factors.
Environmental pollution
Undesirable levels of pesticides in air, soil, water, vegetation and
animal life. This encompasses man, his food and his habitat.
Environmental quality objective
The quality to be aimed for in a particular aspect of the environment,
e.g. ' the quality of water in a river such that coarse fish can maintain
healthy populations'. Un-like an environmental quality standard, the EQO
is not usually expressed in quantitative terms.
Environmental quality standard
The concentration of a potentially toxic substance which can be allowed
in an environmental component, usually air (air quality standard, or water)
over a defined period.
Enzootic
Regularly occurring animal disease of restricted range.
Enzootic disease
A disease (usually in low prevalence) which is constantly present in
a population.
Enzyme
Specific proteins which act as biological catalysts to regulate the
rate of biochemical reactions in all living organisms by lowering the energy
of activation. Enzymes may be biologically synthesised, extracted and
employed to catalyse laboratory or industrial biochemical reactions.
Enzyme-linked immunosorbant assay (ELISA)
A serological test in which the sensitivity of the antibody-antigen
reaction is increased by attaching an enzyme to one of the two reactants.
Enzymic process
(Enzymatic) A chemical reaction or series of reactions catalysed by
an enzyme or enzymes. An enzyme is a protein which acts as a highly selective
catalyst permitting reactions to take place rapidly in living cells under
physiological conditions.
Eosinophilia
Elevated eosinophil count in the circulating blood. Commonly associated
with chronic parasite infections.
Ephemeral
Plant with a short life-cycle, producing several generations in a year;
flowers persisting for one day only.
Epicardium
First larval stage of the isopod suborder Epicaridea; attaches to a
free-living copepod.
Epicuticle
Thin, outermost layer of arthropod cuticle; contains sclerotin but
not chitin.
Epidemic
A widespread and severe, temporary increase in the incidence of an
infectious disease, particularly within a season.
Epidemic ephiphytotic
A progressive but temporary increase in the incidence of a particular
disease within a defined host population.
Epidemic hemorrhagic
Virus disease transmitted by mosquitoes.
Also called denuge fever.
Epidemiology
The science of disease in populations (Vanderplank, 1963); the study
of the development and spread of disease and of the factors affecting these
processes.
Epidemiology, comparative
Studies in which comparisons are made of the influence of host, pathogen
and environment on disease development and spread particularly insofar
as these affect initial inoculum or disease, the length of the latent period,
the length of the infectious period, the numbers of dispersal units formed
and the effectiveness of these units.
Epidemiology, descriptive
Studies, usually of a non-quantitative nature, that depict the behaviour
of disease in populations.
Epidemiology, quantitative
Studies of disease behaviour in populations which utilise measurement
or quantification of states and rates of disease processes.
Epidermal-strip test
An electron microscope technique by which a virus can be quickly examined
in crude-sap extracts. The quick leaf-dip and quick dip techniques are
similar procedures.
Epidermis
Outermost layer of cells on plants or animals.
The outermost, non-vascular layer of the skin.
Epididymis
An oblong body attached to the upper part of each testicle, consisting
of an convoluted tube along which spermatozoa pass from the testis to the
penis and within which they are stored.
Epigenetic changes
Changes in an organism brought about by alterations in the action of
genes. Epigenetic transformation refers to those processes which cause
normal cells to become tumour cells without any mutations having occurred.
Epiglottis
A lid-like structure which covers the entrance to the larynx during
respiration and closes it during deglutition.
Epilepitform fit
A condition in which the animal loses consciousness and has convulsions,
often violent and usually intermittent.
Epilimnion
The upper region of a lake, subject to wind mixing. Above the thermocline.
Epimastigote
Like a promastigote but with a short undulating membrane, such as in
Blastocrithidea.
Epimorphosis
Arthropod development in which all specifically larval forms are suppressed
or passed before hatching; the juvenile that hatches has the adult body
form.
Epinasty
Downward curling of a leaf blade due to cell growth on the upper side
of a petiole being more rapid than that on the lower side; often a hyperplastic
symptom of plant disease (e.g. the disease caused by potato virus Y in
Physalis floridana).
Epipelic algae
Algae living in or on the sediments of a water body.
Epiphyte
Non-parasitic plant that is attached to another plant for mechanical
support only, examples include orchids, lichens and mosses.
Epiphytically
Existing on the surface of a plant or plant organ without causing infection.
Epiphytology
The study of ephiphytotics with special reference to occurrence and
severity of a plant disease as influenced by such environmental factors
as moisture, temperature, wind, the nature of the soil, and so on. Analogous
to 'epidemiology'.
Epiphytotic
An epidemic in a plant (as opposed to epizootic, an epidemic disease
in an animal) the study of which is sometimes known as epiphytotiology.
Epipod
(Epipodite) Lateral process, from the protopod, usually with one or
more joints; may be called an exite.
Episome
An element which carries genetic material, is able to transmit inheritable
traits and to alternate between autonomous and integrated states in the
host cell; in the integrated state an episome is physically associated
with a chromosome, while in the autonomous state it is extrachromosomal.
Epistasis
The suppression of the effect of a gene by a non-allelic gene.
Epitaxis
Bleeding from the nose.
Epitheca
The outer half wall of a diatom cell.
Epithelium
The layers of cells that make up the surfaces of the body, such as
skin and linings of the interior openings of the body (mouth, upper respiratory
tract, gastrointestinal tract, genitourinary tract).
Epitope
The epitope is the location or locations where the antibody binds to
an antigen.
Epizootic
The widespread or simultaneous occurrence of a disease in a large proportion
of an animal population.
Epizootiology
The study of diseases of animals on the basis of mass widespread phenomena.
Equilibrium moisture
The moisture content of grain after it has been exposed content to
a particular environment for an indefinitely long period of time It is
dependent on the humidity and temperature conditions of the environment.
Equitability
Evenness of distribution of species abundance patterns; maximum equitability
occurs when all species are represented by the same number of individuals.
Equity
Assets minus liabilities.
Equity per cent
Equity capital as a percentage of total capital,
i.e. (assets - liabilities)/assets x 100
Eradicant
A chemical or treatment applied to eliminate a pest or pathogen from
its host or environment.
Eradication
Control of a pest or disease by eliminating the organism after it is
established or by eliminating the plants that are its host.
Ergosterol
A major fungal sterol.
Ergot
Members of the grass family may become infected with a fungus, ergot
Claviceps purpurea, which attacks the immature seed head. Ergot
may cause pregnant animals to abort because of uterine contractions. Animals
may develop skin problems due to contraction of the blood vessels. At
lower levels of ingestion in empty stock, sore teats and mouths only may
be seen. Severe effects may require longer periods of ingestion.
Ergotism
A type of poisoning caused by a mycotoxin produced by the fungus Claviceps
purpurea; the toxin is found in contaminated grain and may cause dramatic
neurologic effects as well as decreased blood flow to the extremities.
Erinium
A growth of hairs in dense patches on plant leaves resulting from the
attack of certain Eriophyidae.
Erosion
The wearing away of the land surface by water and wind.
Erosive lesion
A lesion which causes wearing or wasting away of the tissue.
Error of estimation
The difference between an estimated value and the true value.
Erthrocyte
Red blood cell.
Eruciform larva
Caterpillar; a larva with a cylindrical body, well-developed head,
and with both thoracic legs and some abdominal prolegs.
Erumpent
Breaking through (e.g. growth of sporodochia through the epidermis
of susceptible plant organs).
Erythema
A redness of the skin; a rash.
Erythrocytes
The red corpuscles of the blood.
Escape(s)
A plant growing away from cultivation, but not well naturalised.
Failure of inherently susceptible plants to show infestation and damage
even though disease or pest attack is prevalent.
Esodemic
An infestation, in which the host plant is attacked by a parasite that
originated on the plant itself. Opposite of exodemic.
Esophgaus
That portion of the alimentary canal lying between the stoma and cardia;
also known as the pharynx.
Espundia
Disease caused by Leishmania braxiliensis; also called chiclero
ulcer, uta, pian bois, or mucocutaneous leishmaniasis.
Establishment
Sowing or planting a new pasture.
Successful plant (tree) reproduction on a site.
Establishment of natural enemy
The permanent occurrence of an imported natural enemy in a new environment
after introduction as part of a biological control programme.
Ester
A form in which some types of weed-killers may be prepared, notably
2,4-D and 2,4-5T. Weed-killers prepared as esters are not soluble in water.
They are dissolved in oil to which an emulsifier is added so that it may
be diluted with water.
Estivation
The period of suspended animation in many tropical insects and in some
animals in response to hot, dry conditions.
Ether extract
Substances such as fats, oils and waxes that are extracted from plants
with ether.
Etiolation
Excessive spindliness in plants, owing to insufficient light or to
disease.
A phenomenon exhibited by plants grown in the dark; etiolated plants
are pale yellow and have long internodes and small leaves.
Etiology
The study of cause of disease; that phase of plant pathology which
deals with the causal agent and its relations with the susceptible plant.
Eubacteria
One of the three major evolutionary lines of cellular life forms, primarily
procaryotic micro-organisms which possess a peptidoglycan cell wall (mycoplasma
are the only exception).
Eucaryote
A cell or organism having a true nucleus.
One of the three major evolutionary lines cellular life forms, including
plants, animals, fungi, protozoa, and algae, all of which possess a nucleus
and organelles.
Eukarote
Refers to cells of all organisms except bacteria and a blue-green algae.
The nucleus of such cells is separated from the cytoplasm by a nuclear
membrane.
Eukaryote
Organism with membrane-bound nuclei in its cells.
Euler technique
A numerical approximation solution for systems of differential equations
on which the solution is projected forward through time in steps of size
in linear segments of slope f(x,t) given by the differential equation.
Euphotic zone
The upper part of the water column for which there is positive net
photosynthesis by the phytoplankton.
European foulbrood
A disease of larval honey bees caused by the bacteria Streptococcus
pluton.
Eurythermal
Growing over a wide temperature range.
Eutely
Cell or nuclear constancy; the adult has the same number of nuclei
or cells as the first-stage juvenile; eutely may exist in tissues, organs
or entire animals.
Eutrophication
Aquatic plant growth is stimulated to produce excessive choking growth.
The process involves a complex series of inter-related changes in the chemical
and biological status of a water body most often due to a depletion of
the oxygen content caused by decay of organic matter resulting from a high
level of primary productivity and typically caused by enhanced nutrient
input.
Evaginate
Out-pouching; the bulging out, usually under pressure, of a membrane
normally within a body.
Evaporation
In meteorology, the change of liquid water or ice to water vapour.
In certain usages the term signifies only the liquid to vapour phase change,
as distinct from sublimation which signifies the solid to vapour change.
The rate of evaporation is controlled by the water and energy (mainly
solar radiation) supplies and the ability to take up more water.
Evapo-transpiration
Loss of water by evaporation and transpiration from the above-ground
parts of the plant, dominated by meteorological conditions, especially
when water supply is not limiting.
Event
A collection of sample points.
Exanthema
An eruption or breaking out on the skin; a rash.
Exarate pupa
A pupa in which the appendages are free and not glued to the insect
body.
Exclusion
Control of plant disease by excluding the pathogen or infected plant
material from disease-free areas e.g. by seed disinfestation or quarantine.
Excoriate
Loss of substance from for example the skin, by scratching.
Excretion
The process of removal of a compound or its metabolites from the body,
normally via the bile or urine, but also via the lungs for volatile substances
and by either minor routes such as skin, saliva or intestinal mucosa.
Exergonic reaction
A chemical reaction that proceeds with the liberation of heat.
Exflagellation
Rapid formation of micro-gametes from a micro-gamete of Plasmodium
and related genera.
Exite
Lateral process or joint from the protopod, sometimes referred to as
an epipod.
Exodemic
An infestation, or phase thereof, in which the host plant is attacked
by a parasite originating on another plant.
Exogenous
Originating externally, outside the organism.
Arising on the outside of the generating structure.
Exon
A segment of eucaroytic DNA which codes for protein. Contrasted with
introns, the intervening non-coding regions.
Exonuclease
Nucleases that attack the nucleic acid strand starting from the ends
and thus gradually shortening it are termed 'exo' or outside nucleases.
Exopod
(Exopodite) Lateral branch of a biramous appendage.
Exopterygote
Condition of external wing bud development in an insect; also, an insect
in which the wing buds develop externally; associated with hemimetabolous
insects.
Exo-skeleton
The hard structure developed on the outside of, and giving support
to, a body, such as the chitinous covering of an insect.
Exothermic reaction
A chemical reaction that proceeds with the liberation of heat.
Exotic
Alien, introduced from another country.
Exotic species
An organism that evolved in one part of the world and that now occurs
either accidentally or intentionally in a new region i.e. not native.
Exotoxins
Poisonous substances produced by the microbial cell and liberated into
the surrounding environment, without destruction of the cell.
Expected value
Let x be a discrete variable with probability distribution p(x) and
let E(x) represent the expected value of x. Then E(x) = xp(x)/x
Explant
A small piece of a living tissue taken for the purpose of establishing
an in vitro culture. Cell cultures are often identified by the source
of the initial explant: e.g. meristem tip cultures, anther cultures.
Exponential distribution
A probability distribution often used to describe the time between
events in which the probability is highest for events occurring close to
each other. Sometimes referred to as the negative exponential distribution.
Exponential probability distribution
A distribution used to model lifetimes or waiting times in which the
right tail of the distribution decreases expotentially. The probability
function is given as f(x) = e-x x _ 0
Exponential smoothing
In time series analysis a computational method that averages the first
t time series values by increasingly weighting out the contribution of
remote values. The expotentially smoothed value at time t is
t-2
St - _ _ (1 - _)iyt-i + (1 - _)t-1y1
i=0
where y1, y2, .... yt are the response values and _ is the smoothing
constant (0 _ _ _ 1).
Exposure assessment
The process of measuring or estimating intensity, frequency and duration
of human exposures to an agent currently present in the environment or
of estimating hypothetical exposures that might arise from the release
of new chemicals into the environment.
Expotential growth
The phase of most rapid growth, in which the progressive doubling of
cell number results in a continually increasing rate of growth.
Expotential phase
A period during the growth cycle of a population in which growth increases
at an expotential rate.
Expression
The synthesis of a protein or proteins encoded by a particular gene.
Extermination
Complete extinction of a species over a large continuous area such
as an island or a continent.
Extracellular
Outside the cells.
Extra (marginal) capital
Additional capital invested with a view to increasing profit e.g. clearing
land.
Extra (marginal) return
The extra return (revenue) which results from adding one more unit
of input.
Extractable acid
Total acid extractable from a formulation based on an organic acid.
Salts and esters are converted to the parent acid before the determination.
This will also include any free mineral acid.
Extraction buffer
The buffer used in grinding infected leaves during the initial stages
of virus purification.
Exudate
A substance issuing from a tissue either as a normal process or because
of disease in the tissue - usually in plants.
Exules
Heteroecious aphids on their secondary host plant (= alienocolae).
Exuvium
The cast skin of arthropods after moulting.
Eye gnat
Fly of the family Chloropidae.
