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Glossary of Terms

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In parasitoid models, total time initially available for searching.

In parasitoid models, handling time.

Table of random numbers
A table constructed so that each entry is equally likely to be any five-digit number from 00,000 to 99,999. The table of random numbers is used in selecting a random sample.

Solid pesticide formulation in the form of small, flat plates.

Small, merozoite-like stages of Toxoplasma; they develop in the host cells' parasitophorous vacuole by endodyogeny.

A method or procedure, especially the use of adroit devices, for accomplishing an end; in comparison to strategy, tactics is a short-term activity.

Specialisation of metameres in animals, particularly arthropods, into distinct body regions, each known as a tagma.

The northern boreal forest zone, a broad band of coniferous forest south of the arctic tundra.

Unwanted flavour in fresh or processed food.

Take-all decline
The decline in the cereal disease take-all after three or four successive cereal crops.

Take off
The time and method by which a spore enters the atmosphere from a fructification.

Tank mix
Two or more chemical pesticides or formulations mixed in the spray tank at the time of spray application.

The single main root, which grows downward and from which branch roots rise.

The plants, animals, structures, areas or pests to be treated with a pesticide application.

Target organ dose
The amount of a potentially toxic substance reaching the organ chiefly affected by that substance.

Target-pest resurgence
The rapid resurgence of a chemically treated pest population to a damaging level of abundance, brought about by the destruction by the chemical treatment, of the natural enemies that otherwise would have restrained the pest (see resurgence).

Target spot
A lesion consisting of a dark brown circular area containing brown concentric rings. Typical of infection by Alternaria spp.

Tarsal (joint)
The 'hock' joint.

Tarsal setae
Bristles on the legs and feet of some insects, especially flies.

Most distal podomere of the insect or acarine limb that bears the claws of an insect, pl. tarsi.

One component of a R & D project, which may be differentiated from others by the distinct characteristics of its technical results, costs or scheduling.

Task list
A fundamental basis for planning R & D projects - the task list is simply a list of those technical components of a project which may be isolated in discrete categories of technical activity, cost or scheduling.

The staminate or male inflorescence produced at the top of the maize plant.

Movement toward or away from a stimulation.

Any taxonomic entity, such as a species, genus or phylum.

The science of classification and naming of species.

Taylor series expansion
An infinite series representation of a function f(x) in the neighbourhood of a point a involving powers of (x-a) and the derivatives of the function evaluated at a.

T cell
Type of lymphocyte that, on simulation with an appropriate antigen, gives rises to a population of sensitised lymphocytes with receptor sites for that antigen on their surface membranes; so called because they are processed through the thymus; of primary importance in cell-mediated immunity.

Technical grade
Connotes a degree of chemical purity less than that of a material designated chemically pure.

Technical product
The usual form in which a pesticide is prepared and handled prior to formulation; usually at a high level of purity (95-98%) but not completely pure, it may also contain small amounts of necessary additives (see active ingredient).

Technically discrete
Characteristics of a R & D project component which involves a distinct and separate methodology, which can easily be distinguished from the technical work on other components.

The science of controlling forces, both natural and social, to produce desired effects.

Technology assessment
A technique for evaluating the consequences of applying technology to the problems of society.

Dorsal extension over the mouth of a crustacean or acarine; also called the rostrum.

A kicking implement that loosens hay in the swath or windrow to facilitate drying.

The thickened and leathery forewing in the insect orders Orthoptera and Dictyoptera.

Teichoic acid
Acidic polysaccharide containing either glycerol or ribitol, connected by phosphate diester bonds. Found in the walls of gram-positive bacteria.



A resting spore of rust and smut fungi in which sexual fusion occurs and gives rise to a basidium.

A sorus in which teliospores are produced. The fruiting structure in which teliospores are produced.

Blood-feeding arthropod that cuts through skin and blood vessels to cause a small haemorrhage of blood from which it feeds.

The perfect (sexual) state of a fungus.

Temperate virus
A virus which upon infection of a host does not necessarily cause lysis but may become integrated into the host genetic material.

Temporarily holding the paddy between drying passes, allowing the moisture content in the centre of the grain and that on the surface of the grain to equalise.

A sequence of nucleotides in a nucleic acid that acts as a pattern after which a complementary sequence of nucleotides may be formed.

Temporal fossae
Two depressions lying either side of the central line of the head of the horse, just below the crest.

Temporally discrete
Characteristic of a R & D project component which makes it easy to isolate from others in time and sequence.

Temporary parasite
Parasite that contacts its host only to feed and then leaves; also called an intermittent parasite or micro-predator.

Temporary pasture
One grazed for only a short time.

Temporary variables
Simulation model variables that are used in the code or documentation to group together a number of variables for notational or computational convenience.

The property of a deposit or residue to resist removal by weathering or other physical action.

Tenacity index
Ratio of quantity of pesticide residue per unit area at end of given amount of weathering to that present at beginning.

A thread-like organ of climbing plants which attaches itself to some other body so as to support the plant.

Newly emerged adult arthropod that is soft and weak.

Straining; especially ineffectual and painful straining at defecation or urination.

An aerological diagram with cartesian co-ordinates T (temperature) and log Ø (potential temperature).

Substance that causes physical birth defects in the offspring following exposure of the pregnant female.

Defects in embryonic and foetal development caused by a substance.

The science concerned with malformations and monstrosities.

Functional unit of hymenopteran ovipositor, formed from first and second valvulae.

Main dorsal sclerite of a somite of an arthropod.

The dorsal body sclerite of an insect, pl. terga.

Terminal disease
A disease which ends the life of an organism.

Terminal oxidation
The oxidation of respiratory substrates and intermediates by the transfer of electrons (plus H+ ions) via various carriers to compounds (cytochromes) which are capable of yielding electrons to O2, forming H2O.

A nucleotide sequence in DNA that causes mRNA to detach and thus functions to stop transcription.

A class of hydrocarbons characterised by (C5H8)_ and occurring in plant oils and resins.

An embankment or channel built across a slope, approximately on the contour, to prevent water off-run.

An area of land; including its geological formation, its vegetation and animal life.

Tertian malaria
Malaria in which fevers recur every 48 hours. Caused by Plasmodium vivax, P. ovale, and P. falciparum.

Tertiary consumers
Animals high on the food chain that consumer predators, eg. hawks.

Tertiary parasite
A parasitoid that develops in or on a secondary parasite.

The external coating of a seed.

Test statistic
A function of a sample of observations that provides a basis for testing a statistical hypothesis.

Strigeoid metacercaria in the family Strigeidae.

Having four times (4n) the basic number of chromosomes or twice the diploid number (2n).

Having one or a few chromosomes tetraploid in otherwise diploid nuclei.

Describing an arrangement of cells in certain algae in which the individual cells are embedded in a mucilage.

Only metacestode form known in the tapeworm cyclophyllidaen genus Mesocestoides; a large, solid-bodied cysticercoid.

The plant-like structure of a fungus or alga, usually macroscopic in size.

Disease of cattle and other ruminants, caused by Theileria parva; also called East Coast fever.

That pattern or mode of parthenogenetic reproduction in which unmated females produce only female progeny, males being unknown (opposite of arrhenotoky, where only males are produced, eg. in honeybee).

Treatment of disease.

Thermal death point
That high temperature at which death of an organism occurs under a specified length of time, usually 10 minutes.

Thermal death time
Time at a particular temperature required to kill all cells in a population.

Thermal inactivation point
The lowest temperature at which heating for a limited period (10 mins), is sufficient to cause loss of virus infectivity.

Thermal loading
The increased temperature in a water body caused by power plant cooling systems.

The water depth in a stratified lake at which the temperature changes very rapidly between the epilmnion and hypolimnion.

Able to survive specific high temperatures but not grow.

An organism living at high temperature.

Maintenance or regulation of temperature, specifically the maintenance of a particular temperature of the living body.

Thoracic cavity
The cavity enclosed by the rib cage and diaphragm, lined by the pleura, and in which the heart and lungs lie.

That portion of an insect's body which lies between the head and abdomen and bears the legs and wings. The chest; the part of the body between the neck and the abdomen.

Three-day fever
Virus disease transmitted by sand flies; also called sand fly fever.

Three-way cross
A cross between a single-cross hybrid and an inbred line.

The level of some independent variable at which some process changes from one distinct state to another, eg. a temperature threshold above which fish feeding ceases.

Threshold concentration for control
Developing the concept of herbicide chronicity, it is defined as the sustained minimum concentration of herbicide required over an extended period to inhibit plant growth and produce control.

Threshold dose
The dose at which an effect just begins to occur, ie at a dose immediately below the threshold dose the effect will not occur, and immediately above the threshold dose the effect will occur. The threshold dose will fall between the experimentally determined no-observed-effect level and the lowest-observed-effect level. It is important when using the no-observed-effect level or lowest-observed-effect level, to specify which effect is being measured, in what population and the route of administration. Both the no-observed-effect level and the lowest-observed-effect level have been used by different scientific groups as a surrogate for the threshold dose in the performance of risk assessments.

Threshold limit value- time weighted average
The time-weighted average concentration for a normal 8-hour workday and a 40-hour work-week, to which nearly all workers may be repeatedly exposed, day after day, without adverse effects.

Blood clot in blood vessel or in one of the cavities of the heart.

Throughput capacity
The amount of paddy which flows through a continuous flow dryer in one hour.

Photosynthetic lamella; the internal membrane of chloroplasts, with which chlorophyll is associated.

The long, slim segment of an insect's leg to which the tarsus is attached. Podomere of an insect or acarine leg that articulates proximally with the femur in insects and patella in acarines and distally with the tarsus in insects or with the metatarsus or tarsus in acarines.

The use of implements to cultivate the soil in the preparation of seed-beds and root-beds for crops.

A sprout or stalk, especially one from the base of a plant or from the axils of its lower leaves.

The physical condition of a soil in relation to its fitness for the growth of a crop. When in good tilth, a soil is mellow, friable and easily worked.

Time scale
The run time of a model.

Time series
Any sequence of measurements taken on a variable process over time. Usually illustrated as a graph whose vertical co-ordinate gives a value of the random response plotted against time on the horizontal axis.

Time series analysis
A term applied to a number of different forecasting methods.

Time step
The unit of time used in a numerical approximation to a differential equation.

Time traces
Graphs of model behaviour or of data from the ecosystem over time.

A group of cells of similar structure which performs a special function. A collection of cells which compose a defined region of the anatomy of a plant or animal.

Tissue culture
In vitro methods of propagating cells from animal or plant tissue (see in vitro).

The strength or quantity of a chemical substance in solution.


The ability of an organism to sustain the effects of a disease or pest attack without dying or suffering serious injury or yield loss. Also, the amount of toxic residue allowable in or on edible plant parts under the law, formerly used to describe maximum residue limit.

Tolerance, permitted
Maximum content of toxicant allowed (eg. of lead and arsenic) in foodstuffs for human consumption.

Capable of withstanding effects e.g. grasses are tolerant of 2,4-D to the extent that it can be used selectively to control broad-leaved weeds in cereals, pastures and turf (see tolerance).

Science of weed control.

Top cross
A cross between an inbred line and a random bred variety or strain.

A fertiliser application on a crop any time after planting.

Topical application
A technique for applying small measured amounts of pesticide to the surface of individual organisms. Application is made usually as small drops (about 1-2 placed on some specific part of the organism e.g. a leaf blade or insect thorax.

The capacity of a cell to differentiate into all of the cells of the adult organism.

Features of the natural land surface.

The surface portion of the soil, usually the average plough depth, which may also include the sub-surface soil that contains organic matter.

Wryneck; a contraction of neck muscles which produces a twisting of the neck and an unnatural position of the head.

Total digestible nutrients (TDN)
The sum total of all the digestible nutrients in a feed.

Total drift
The volume (or mass) of chemical per unit length of spray run leaving the field or target area in the form of target drops.

Total (non-selective) herbicides
A herbicide used in such a way as to kill all vegetation eg. sodium chlorate. They are used to eliminate weeds from industrial sites, railway tracks, paths etc.

Total milling yield
Total rice, including head rice and broken rice milled from paddy usually expressed as a percent.

Total population curve
The total population density of individuals of all stages plotted against time.

The toxic component of an insecticide molecule. That part of the molecule rendering toxic properties to the compound.

A condition produced by the dissemination of toxins in the blood.

Poisonous; injurious to animals and plants through contact or systemic action.

A toxic substance such as the active ingredient in pesticide formulations, that can injure or kill plants, animals or micro-organisms.

Degree to which something is poisonous; the ability of a material to interfere adversely with the vital processes or an organism.

Toxicity chronic
That which is manifest when toxicants act upon the body over a long period of time such as daily exposures.

Toxicity coefficient
MacCuaig (1969) coined the term 'toxicity coefficient' for evaluating insecticide formulations developed for locust control. This he defined as half the number of LD50 doses per litre, or the number of locusts which a litre of formulation would kill if all the LD50 doses it contained were applied as contact insecticide to a series of individual locusts. Generally, a method of expressing the toxicity of new materials compared to a standard: Toxicity Coefficient = dosage required for 50% kill with standard dosage required for 50% kill with new material.

Toxicity oral
A poison reaction resulting from oral intake of pesticide.

The science (branch of physiology) devoted to the study of chemical substances which exert deleterious effects on living organisms; their chemistry in relation to their mode of action, antidotes and physiological effects.

The active process of identification, investigation and evaluation of the various toxic risks in the community with a view to taking measures to reduce or eliminate these risks.

The characteristic of certain harmful organisms to produce toxic substances with pathogenic effects on men or animals.

The degree to which an organism is able to elicit toxic symptoms.

An organic substance usually acting at low concentration, usually produced by a living organism and irreversibly affecting the normal processes of a living organism.

Any disease caused by the action of a toxin.

A toxin modified so that it is no longer toxic but is still able to induce antibody formation.

The toxic component of a toxic molecule, or that portion of a molecule responsible for its toxic action.

In general anatomical usage, a septum extending from an envelope through enclosed substance, which, together with other trabeculae, forms part of the framework of various organs; also called intermuncial process.

Trace element
Chemical element used by organisms in minute quantities and essential to their physiology.

Additive to facilitate location of deposit eg. radioactive or fluorescent material.

The wind-pipe; the cartilaginous and membranous tube extending from the larynx to the bronchi.

The larger respiratory tubes leading from the spiracles in insects.

Tracheal ring
Each of the rings of cartilage placed one after another and connected by fibrous-tissue and membrane, which make up the trachea.

Tracheal system
System of cuticle-lined tubes in many insects and acarines that functions in respiration; opens to outside through spiracles.

An elongated, tapering xylem cell which conducts water and provides mechanical strength in plants.

Tracking powder
A rodenticide contact formulation in powder form.

Trade name
Name given to a product sold by a company to distinguish it from similar products made by other companies (also trademark name, proprietary name, brand name).

Traffic offered
The ratio of the arrival rate to the service rate in queuing model.

The encapsidation of the nucleic acid of one virus strain with the protein of another, during simultaneous infection and replication of two strains.

The process of RNA synthesis by RNA polymerase to produce a single-stranded RNA complementary to a DNA template.

The transfer of genetic material from one bacterium to another by means of a bacteriophage.

Transfer of symbiotic fauna (usually mutualistic protozoa) from one host to another.

Transfer RNA (t-RNA)
The RNA that carries amino acids to the ribosome to be placed in the sequence prescribed by the messenger RNA.

A genetic engineering procedure whereby a piece of foreign DNA is transferred to a cell thus conferring upon it novel characters. Also, the change of a normal to a malignant cell.

An organism whose genome has been altered to include new genes from the same or different species.

Situation in which farmers with a permanent place of residence send their herds, tended by herdsmen, for long periods of time to distant grazing areas.

Transition matrix
A matrix of probabilities of one time step transfers between states of the system.

Translaminar (activity)
A pesticide which passes through the leaf tissue from one surface of a leaf to the other.

The process during protein synthesis in which the genetic code in messenger RNA is translated into the polypeptide sequence in protein.

The process whereby the genetic code present on the m-RNA molecule directs the order of the specific amino acids during protein synthesis or transfer of solutes or other materials such as pesticides from one part of a plant to another.

The transfer of an infectious agent (usually a virus) from one plant to another. The dissemination of pathogens and the inoculation of suscepts.

Via the ovary; especially in relation to the ability of some micro-organisms to be carried from one generation of arthropods to the next via the egg of the arthropod.

Transovarial transmission
When virus is transmitted through the eggs of the infected vector to its progeny.

Transovarian transmission
A mode of transovum transmission in which the passage of micro-organisms from mother to egg is known to occur within the ovary. Transmission of a virus from an adult organism to its progeny through the ovaries and eggs.

The transmission of micro-organisms from one generation to the next by way of the egg. Transovarian transmission is a special case of transovum transmission.

The evaporation of moisture from a living plant, mainly through the stomata of the leaf. This moisture represents a surplus from that taken in by the roots and which is not required for photosynthesis.

Transport host
An organism which transports a pathogenic micro-organism to which it is not susceptible; also, a mechanical vector.

Transposable elements or transposon
Sections of DNA that can move from one place to another on one chromosome or move between chromosomes. Sometimes called 'jumping genes'.

Transposon mutagenesis
Insertion of a transposable element within a gene generally leads to inactivation of that gene resulting in the appearance of a mutant phenotype.

Trap crop
Crop planted to attract insect pest and, when infested, collected and destroyed or controlled by pesticide applications. The trap plants are usually grown between the rows of crop plants or else peripherally.

The removal of individuals from a pest population, in significantly large numbers, by means of trapping.

When virus is retained through the moult of its insect vector.

Transstadial transmission
The transmission of micro-organisms from one stage of the host to the next, throughout part or all of the host's life cycle.

Wounds or injuries caused directly by violent contact of external objects with the body of the animal.

Pertaining to injury; especially to injuries of mechanical rather than disease origin.

Any area upon which a toxic material has been applied, or some means of control has been established.

A stimulus that is applied in order to observe its effect on the experimental situation. A treatment may refer to a physical substance, a procedure, or anything capable of controlled application according to the requirements of the experiment.

Treatment threshold
The critical level of pest or disease intensity requiring control measures to avoid crop losses.

(Pertaining to classification) The category used in classification which is subordinate to a class and superior to a family.

Tribocytic organ
Glandular, pad-like organ behind the acetabulum of a strigeoid trematode.

Tricarboxylic acid
A series of steps by which pyruvate is oxidised completely to CO2, also forming NADH, which allows ATP production.

In some algae, lichens and fungi, a projection from the female sex organ that receives the male gamete or nuclei before fertilisation.

Epidermal outgrowth eg. leaf hair. In bacteriology, generally equivalent to a filament.

A type of flagellated protozoan, which inhabits the gastrointestinal or urinary tract; one type causes an extremely common sexually transmitted disease called trichomoniasis.

Trickling filter
An oxidative process for the treatment of sewage; liquid sprayed onto a rock bed is oxidised by microbes growing on the rock surface.

Trickling filter fly
Psychoda alternata, a common fly that breeds in sewage and similar habitats.

Any of an order Tricladia of turbellarian platyhelminths, distinguished by having one anterior and two posterior branches of the intestine.

Small metal probe for taking samples of paddy or rice or from bulk containers.

Trifoliate leaves
The leaves of clover or lucerne that are formed from three leaflets.

Ventral, bristle-like sensory organ just behind the gnathosoma of a mesostigmatid mite.

Triungulin larva
The active first instar larva of some parasitic, hypermetamorphic Neuroptera and Coleoptera and of the Sterpsiptera.

Trivial name
Name in general or commonplace usage; eg. nicotine.

Podomer of insect or acarine leg that articulates distally with the femur (usually fixed to the femur in insects).

Trophic level
Functional classification of organisms in a community according to feeding relationships; the first trophic level includes green plants; the second trophic level includes herbivores the third carnivores.

Active, feeding stage of a protozoan, in contrast to a cyst; also called the vegetative stage.

True leaves
Leaves which are not cotyledons (seed leaves).

System of air ducts eg. in mist-blower.

One type of flagellated protozoan; includes the causal agent of African sleeping sickness, an infection of the bloodstream.

Form of Trypanosomatidae with an undulating membrane and the kinetoplast located posterior to the nucleus, eg. Trypanosoma.

Tsetse fly
Bloodsucking fly of the genus Glossina.

The swollen portion of an underground stem or root which acts as a storage organ and propagule; it is usually of one year's duration, those of successive years not arising directly from the old ones nor bearing any constant relation to them.

A projection. Rounded protuberance.

Mosquito pupa.

Tumbu fly
African Callophoridae, Cordylobia anthropophaga.

A term used for abnormal tissue formations in insects and other invertebrates which have characteristics in common with vertebrate neoplasms but whose precise nature is unknown.

Any swelling, whether oedema or a mass, resulting from malformation, inflammation or repair; may be either benign or malignant.

Causing tumour formation.

Treeless area in arctic and alpine regions, varying from bare area to various types of vegetation consisting or grasses, sedges, forbs, dwarf shrubs, lichens and mosses.

(Of the atmosphere) Quality or state in which the air flow at a given point changes constantly in velocity and direction (contrasted with laminar flow).

A sod. The upper portion of soil filled with the roots and stems of low-growing, living plants.

Swollen with water.

Turgor pressure
The pressure exerted against the wall of a plant cell by the fluid contents of the cell.

Alternative terms for the value of sales within a period of time.

Turnover of capital
The relationship of sales to capital employed, stating the number of times each £1 of capital has generated £1 of sales in one year.

Non-ionic surfactants chemically resembling Spans, but rendered more hydrophilic by the addition of a polyoxytheylene chain.

Two-stage cluster sample
A two-stage cluster sample is obtained by choosing a simple random sample of clusters and then selecting a random sample of elements from each cluster.

Two-tailed statistical test
A statistical test of an hypothesis in which the rejection region is separated by the acceptance region and is located in both ends of the distribution of the test statistic.

A balloon-like intrusion into the lumen of a xylem vessel, formed by enlargement of an adjacent living cell and its extrusion through a pit in the vessel wall.

A balloon-like overgrowth of the protoplast of a parenchyma cell into an adjacent xylem vessel.

A ringing note; the condition of distension of the abdomen with gas, and which when tapped produces a ringing note.

Type I error
In the statistical test of an hypothesis the error incurred by rejecting the null hypothesis is true.

Type II error
In the statistical test of an hypothesis the error incurred by accepting the null hypothesis when the null hypothesis is false and some alternative to the null hypothesis is true.

Type specimen
The original collection of an organism on which the description of a new species is based.

Typical host
A host in which the pathogenic micro-organism (or parasite) is commonly found; synonymous with natural host.