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[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]

'a' Area of discovery
A constant (see Nicholson-Bailey model) or the probability that a given predator will encounter a given prey during its searching lifetime or the total area effectively searched for hosts by a parasite throughout its lifetime (Hassell, 1978). a is dimensionless unless expressed as numbers per unit area then it will have the same units of area.

'a' Coefficient of attack
An instantaneous rate of encountering hosts. It becomes the area of discovery when multiplied by searching time (Hassell, 1976).

Abaxial
The leaf surface facing away from the stem of the plant.

Abbott's formula
A formula to adjust for mortality not associated with insecticide treatment such as the natural mortality in an untreated control group, or mortality occurring from a blank spray used as a check. Adjusted % mortality = % alive in check - % alive in treatment x 100% alive in check.

ABC Analysis Bar
A combination of the bar chart and networking

Charting
approaches to planning. Useful for calculating actual dates for commencement and completion of all tasks in a project, as well as isolating the critical path (see Critical path/analysis).

Abiotic
Non-living, physical or chemical, includes solar radiation, temperature, humidity, and pH, used in context of an effect eg. abiotic damage.

Abnormality
A deviation from the normal, a malformation or teratology, a state of disease.

Abomasum
The fourth stomach of a ruminant, sometimes known as the true stomach.

Abrasion
In toxicological terms, the laceration or scratching of the waterproof layer of cuticle allowing moisture from the insect to be lost to the surrounding air.

Abrasive polisher
A machine that uses abrasive action between the kernel and the emery stone to remove the bran from the rice kernel.

Abscission
Process by which leaves, stems or fruits are separated from the parent plant.

Abscission layer
A zone of delicate, thin-walled cells surrounding a lesion on a leaf, stem or fruit, the breakdown of which disjoins the affected area from the rest of the plant.

Absorption
The penetration of a substance, eg. gas or thin film of liquid, into the surface layer of a solid with which it is in contact eg. process by which pesticides are taken into plant tissues by roots or foliage (stomata, cuticle, etc.).

Absorption costing
A costing technique where the costs to develop a product are taken to include both direct (eg. manufacturing costs) and indirect costs (eg. administrative expenses).

Absorbtive clay
A special type of clay powder which can take up chemicals and hold them. It is sometimes used to clean up pesticide spills.

Acanthella
Developing acanthocephalan larva between an acanthor and a cystacanth, in which the definitive organ systems are developed.

Acanthor
Acanthocephalan larva that hatches from the egg.

Acaricide (miticide)
Any chemical, agent or material toxic to mites, ticks and spiders (Acarnia) as distinct from insects.

Acarine disease
A disease of adult bees caused by the parasitic mite Acarpis woodi.

Acceptable daily intake
The daily ingested intake of a pesticide (expressed as mg/kg body weight per day) that, over the entire lifetime of a human being, standard man = 60 Kg, appears to be without appreciable risk on the basis of all known facts at a specified time.

Accession
A new member to a plant collection. In the context of plant pathology and plant breeding, accessions are often tested for disease resistance.

Accessory pigments
Coloured compounds which absorb and transfer light energy to chlorophyll.

Accidental host
An uncommon or rare host to a pathogenic microorganism.

Accidental myiasis
Presence within a host of a fly not normally parasitic. Also called pseudomyiasis.

Accidental parasite
Parasite found in other than its normal host. Also called an incidental parasite.

Accidental species
An occassional species in a particular community type; not a good species for use in community definition (see characteristic species).

Accounting
The administrative task of recording actual costs and expenditures so that comparisons may be made to budgets (planned costs and expenditures) for the sake of financial control.

Acervulus
A sub-epidermal, cushion-like mass of hyphae containing asexual condiophores that bear conidia formed by some imperfect fungi.

Acetabulum
Sucker such as the ventral sucker of a fluke or a sucker on the scolex of a tapeworm.

Acetogenic bacteria
Bacteria capable of reducing CO2 to acetic acid or converting sugars quantitatively into acetate.

Acetylcholine (ACh)
Chemical transmitter of nerve and nerve-muscle impulses between nerve and across nerve-muscle junctions. In normal nerve activity it is hydrolysed by the enzyme cholinesterase after each impulse.

Acid-alcohol fastness
A staining property of Mycobacterium species where cells stained with a hot phenolic solution of basic fuchsin will not decolourise with dilute acid.

Acid equivalent
The total organic acid content of a substance expressed in terms of the active acid. In herbicide concentrates, it is the content of active ingredient expressed as a free acid.

Acidophile
Any organism that grows best under acidic conditions (low pH).

Acid soil A soil with a reaction below a pH of 7.0 ie. it has more hydrogen ions than hydroxyl ions.

Acquired immunity
Immunity which develops in response to foreign antigens in the body, involving either the production of antibodies or activated T cells which react specifically with the foreign antigen.

Acquired resistance
(Induced resistance or acquired immunity) A resistance response developed by a normally susceptible host following a pre-disposing treatment, such as inoculation with a virus, fungus, bacterium or treatment with certain chemicals. This resistance is not inherited.

Acquisition
The entry of virus into, or attachment to, a vector.

Acquisition feeding time
The feeding time during which a vector feeds on an infected plant to acquire a virus for subsequent transmission (eg. to become viruliferous).

Acquisition threshold period
The minimum feeding time for a vector to become viruliferous.

Acropetal
Describes the development of structures (such as spores) in succession from the base towards the apex.

Actinomycetes
A group of microorganisms apparently intermediate between bacteria and fungi, and classified as either. Characterised by fine hyphae, usually less than 1.0 µm in diameter, that readily break into fragments resembling bacterial cells. Gram-positive, irregularly staining filamentous bacteria with true branching that do not form spores and are non-motile.

Activation energy
Energy needed to make substrate molecules more reactive eg. enzymes function by lowering activation energy.

Activator
A substance added to a pest control material that increases its toxicity and results in more effective control.

Active acid
An active ingredient which is an organic acid (normally formulated as a salt or ester, so that the same weight of active ingredient may be present in different weights of salt or ester).

Active immunity
An immune state achieved by production of antibodies in the host. Compare with passive immunity.

Active ingredient (a.i.)
Toxic component of a formulated pesticide.

Active resistance
Resistance resulting from host reactions occurring in response to the presence of the pathogen or its metabolites.

Active site
The portion of an enzyme which specifically combines with the substrate.

Activity-based costing
The identification of activities as a basis for charging overhead costs to products.

Activity ratio
Used in standard costing to express the actual work produced as a percentage of the budgeted work for the same period when both are expressed in standard hours.

Activity sampling
A work measurement technique to produce standard work times for planning, pricing and incentive payment schemes.

Acute
Of short duration, characterised by sharpness or severity; as opposed to chronic.

Acute toxicity
The toxicity of a material determined at the end of 24 hours; toxicity that causes injury or death from the single dose or exposure.

Adaptation
From an evolutionary stand-point, it is a characteristic of a living organism that improves its chances for survival in the environment of its habitat; change brought about in a population or an organism as a result of exposure to a particular set of environmental conditions, the change enabling the organism to adjust to the environmental conditions.

Adaxial
The leaf surface facing the stem of the plant.

Additive effect
An effect which is the result of two chemicals acting together and which is the simple sum of the effects of the chemicals acting independently.

Additive resistance
Resistance governed by more than one gene, each of which can be expressed independently, but which is reinforced by the expression of each of the additional genes.

Adherence
The ability of a material eg. a pesticide, to stick to a particular surface.

Adhesive (syn. Sticker)
Material added to increase surface retention (persistence) of a pesticide. Their value in the field is not clearly proved even for fungicides where they are mainly used.

Adiabatic process
A thermodynamic change of state of a system in which there is no transfer of heat across the boundaries of the system. Compression always results in warming, expansion in cooling.

Adjuvant
An ingredient that improves the properties of a pesticide formulation. Includes wetting agents, spreaders, emulsifiers, dispersing agents, foam suppressants, penetrants and correctives.

Adjuvant vaccine
A substance added to a vaccine that enhances the effect of the antigen. Generally, adjuvants slow down the rate at which the antigen is released into the system thus giving a prolonged and enhanced immunity eg. potassium alum and lipid emulsions.

Adoptive immunity
Immune state conferred by inoculation of lymphocytes, not antibodies, from an immune animal rather than by exposure to the anitgen itself.

ADP (Adenosine diphosphate)
A compound which upon phosphorylation (addition of phosphate and energy) forms high energy bonds as ATP.

Adsorb
To gather on a surface (opposed to absorb).

Adsorption
The chemical and/or physical attraction of one substance at the surface of another. Refers to gases, dissolved substances or liquids on the surface of solids or liquids. eg. the tendancy of clay and high organic soils to absorb pesticides.

Adulterate
To reduce the purity of a material below the standards it is supposed to represent. Also to leave out any ingredient necessary for the effectiveness of the material or the substitution of other materials eg. a pesticide that does not conform to the professed standard or quality as documented on its label or labelling.

Adulticide
Toxic materials that are most effective in the control of the adult stage of arthropod pests.

Adult plant resistance
Resistance detectable in adult plants ie. later stages of development (mature plant resistance or age resistance). Generally attributed to horizontal resistance. See also field resistance.

Advection
The process of transfer (or an air mass property) by virtue of motion. In particular the horizontal or vertical components of the motion. The term is, however, often used to signify horizontal transfer only.

Adventitious
Roots or buds arising from an unusual position on a stem eg. roots on stems, or buds produced elsewhere than in the axils of leaves or the extremities of stems.

Adverse effect
An undesirable or harmful effect to an organism, indicated by some result such as mortality, altered food consumption, altered body and organ weights, altered enzyme levels or visible pathological change.

Aecidium
A cup-shaped aecium that contains a peridium.

Aeciospore
An asexual, dikaryotic rust spore produced in an aecium.

Aecium
A cup-shaped fruiting body of rust fungi eg. Puccinia graminis in which aeciospores are produced. Aecia may be of the aecidium, caeoma, peridermium or roestelium type.

Adeeagus
Copulatory organ or penis in insects and mites.

Aeration
The moving of air through stored grain at low airflow rates (generally between .07-.28 m3/minute per ton), to maintain or improve its quality.

Aerial roots
Roots that arise from the above ground

Aerobic
An organism requiring free oxygen for respiration eg. areobic bacteria, may be facultative or obligate.

Aerophobic
An organism harmed by oxygen; an obligate anaerobe.

Aerosol
Air suspension of solid or liquid particles having a volume median diameter of less than 50 µm. Aerosol sprays are principally used for drift spraying against flying insects. The small size of the droplets or particles allow entry to the body via the respiratory tract and readily contaminates clothing, skin and eyes.

Aerosol dispenser
Container holding a pressurised formulation which produces aerosol spray due to volatisation of a propellant when a valve is opened.

Aerosol sprayers
Sprayers using a blower unit to generate an aerosol spray.

Aestivation
Condition in which an organism may pass an unfavourable hot or dry season (the opposite of hibernation) and in which its normal activities are greatly curtailed or temporarily suspended.

Aetiology
The science of the investigation of the cause

Aflatoxins
Myotoxins produced by the fungi Aspergillus flavus.

Aftermath
Second crop of grass cut from a field in a season.

Agamic
Parthogenetic reproduction; without mating.

Agar
A polysaccharide obtained from certain seaweeds. Agar forms a gel with water, and is used at a concentration of 1.5-2.0% to solidify media used for culturing micro-organisms.

Agent of inoculation
An agent which transports inoculum from its source to or into the infection court eg. wind, splashing rain, running water, insects, man or other animals.

Agglomerate
Particles bound firmly together.

Agglutination
A serological test in which viruses or bacteria suspended in a liquid clumps together whenever the suspension is treated with anti-serum containing antibodies specific against these viruses or bacteria.

Aggregate
Particles adhering loosely together eg. a crumb or clod of soil.

Aggregation
Coming together of organisms into a group eg locust swarms.

Aggressiveness
A measure of the rate at which a virulent isolate produces a given amount of disease.

Agistment
Grazing one's animals on land controlled by another person, for the payment of a fee either in cash or in kind.

Agitator
A mechanical device in a spray tank to ensure uniform distribution of the toxicant during dilution and to prevent sedimentation.

Aglycone
An organic compound, usually a phenol or an alcohol, combined with the sugar portion of a glycoside and obtainable by hydrolysis eg. DIMBOA 2,4-dihydroxy-7-methoxy-2H-1,4-benzonxazin-3-one in maize.

Agonist
A chemical with a positive action in the body.

Agricultural chemical
A broad term used to cover pesticides, adjuvants, conditioning agents and other chemical tools used in improving agricultural production, protecting crops or controlling pests, diseases and physiological conditions of crop plants. It does not normally include fertilisers.

Agricultural commodity
Any plant or part of a plant, animal or animal product that is to be bought or sold.

Agro-ecology
The study of ecology in relation to agricultural systems.

Agro-ecosystem
The ecosystem composed of cultivated land and surrounding or intermixed uncultivated areas, the plants contained or grown thereon, and their associated animals.

Agrology
Study of the applied aspects of soil science and management.

Agronomy
Science of soil management and crop production.

Air-blast nozzle
See nozzle i.

Air-blast sprayer
See sprayer i.

Airborne concentration
The amount of chemical per unit volume of air. Typically this refers to the volume or mass concentration of chemical, but it can refer to the number concentration of spray drops.

Airborne drift
The volume (or mass) of chemical per unit length of spray run that passes above a point at a given down-wind distance outside the field or target area.

Airborne flux
The amount of chemical passing perpendicularly through a given area per unit time. If the area is vertical, then the chemical is moving horizontally (eg. drops moving down-wind) and causes a horizontal flux. Alternatively, heavy drops falling towards the ground pass through a horizontal area and provide a vertical flux.

Air-carried spray
See spray i.

Air-carrier spray
See sprayer ii.

Air spora
The population of airborne particles of biological origin.

Akinete
A resting spore of cyanobacteria.

Ala
Term often applied to wing-like structure on plants or animals eg. cuticular expansions of nematodes.

Alatae
Winged forms of aphids, usually referring to winged parthenogenetic females.

Alate fundatrigeniae
Winged parthogenetic female aphids migrating from a primary to a secondary host plant (= spring migrants).

Albication
Whiteness; a hypoplastic symptom of plant disease characterised by the failure of colour to develop in organs that are normally coloured.

Alcohol
Although in ordinary conversation ethyl alcohol is generally referred to merely as 'alcohol' that term applied to a long series of hydroxy organic compounds beginning with the one-carbon compound methanol, or methyl alcohol. Both methyl and ethyl alcohols are common solvents frequently used in formulating pesticidal mixtures.

Aleurone
The proteinaceous and fatty material of the outer-most cell layer of the enodsperm of ripe, small grains.

Alga
Aquatic plants or plants of damp habitats having unicellular and multi-cellular forms that are distinguished from the fungi by the presence of chlorophyll.

Algal bloom
Extremely heavy algal growth in a body of water.

Algicidal
A material toxic to algae; usually a type of anti-microbial agent.

Algicide
A chemical used to control algae, often referred to as aquatic weeds.

Algorithm
A structured series of procedural steps necessary for solving a problem eg. a list of instructions or a flowchart (diagrammatic representation of an algorithm).

Alienecolae
Heteroecious aphids on their secondary host plant.

Alien species
An organism that has invaded or been introduced by man and is growing in a new region.

Aliphatic
A descriptive term for chemical compounds composed of straight chain molecules.

Alkaline soil
One which contains alkali salts, usually in amounts that are detrimental to crop growth. Such soils are usually above a pH of 8.5.

Alkaloid
A group of plant derived substances with toxic properties, eg. pyrethrum.

Alkalophile
Any organism that grows best under alkaline conditions.

Alkylating agent
A substance that introduces an alkyl radical into a chemical compound in place of a hydrogen atom.

Allele
Abbreviation of allelomorph. One of a pair of characters that are alternative to each other in inheritance, located on the same locus (position) of homologous chromosomes.
Allelochemic
As defined by Whittaker (1970), a non-nutritional chemical produced by an individual of one species that affects the growth, health, behaviour, or population biology of another species.

Allelopathy
Influence of plants upon each other, through the release of products of metabolism that inhibit the growth of adjacent plants.

Allergic klendusity
Disease-escaping ability produced by development of hypersensitivity to an antigen (allergen).

Allergy
An unusual sensitivity to a substance normally harmless to others. The host mounts an immunologic response against an allergen and reacts whenever exposed to it. Usually caused by a foreign antigen in food, pollen or chemicals.

Allocation
The actual supplying of money so that R & D work may commence.

Allocation of costs
The charging of all the cost elements to a cost centre or cost unit.

Allochthonous
Exotic or introduced (opposite of auto-chthonous).

Allograft
Graft of a piece of tissue or organ from one individual to another of the same species.

Allometric consumption function
The relationship between consumption rate and animal body size.

Allometric length-weight relationship
The relationship between the weight and the length of an organism.

Allomone
An allelochemic that induces a response in an individual of another species (e.g. an insect) that is beneficial to the emitting organism (e.g. a plant). Many allomones are essentially deterrents. However, a scent that attracts bees and therefore facilitates pollination is also an allomone (See also Kairamone).

Allopatric
Having separate and mutually exclusive areas of geographical distribution (opposite of sympatric).

Allopolyploid
A polyploid with more than two sets of chromosomes, each being derived from a different species.

Allosteric
Characteristic of some proteins, especially enzymes, in which a compound combines with a site on the protein other than the active site, resulting in a change in confirmation at the active site.

Allotetraploid
Amphidiploid, i.e., having a complete diploid chromosome set from each parent strain as a result of chromosome doubling in the first hybrid generations.

Alopecia
Baldness, a deficiency of hair.

Alternate grazing
Grazing two pastures in alternate succession.

Alternate host
One of the two hosts of a pathogen where different stages of the life cycle occur on unrelated hosts. When several or many plant species are hosts of a given pathogen they are known as alternative hosts.

Alternate husbandry
An agricultural system where land is cropped for 2-5 years and then sown to pasture mixtures (leys) for 2-5 years. A stable form of agriculture slowly replacing shifting cultivation.

Alternations
The population density alternates between high and low values in successive generations if the key factor is density dependent and strongly over-compensates for a change in population density.

Aluerone layer
The outer layer of cells of the endosperm of seed, such as maize and wheat. This layer is filled with aleurone (protein) grains.

Amastigote
Form of trypansomatidae that lacks a long flagellum. Also called a Leishman-Donovan (L-D) body, as in Leishmania.

Ambient air
The air of the surrounding environment.

Ambient conditions
The air temperature, wind speed and humidity immediately surrounding the subject e.g. a crop.

Ambient temperature
The temperature of the surroundings averaged over 24 hours.

Amebula
Daughter cell resulting from mitosis and cytokinesis of an encysted amoeba.

Amendments
The addition to soil of materials, usually with the aim of suppressing disease.

Amensalism
A type of symbiotic relationship in which one of the partners in the interaction is inhibited and the other is unaffected.

American foulbrood
A disease of larval honey bees.

Ametabola
Insects which do not undergo a metamorphosis (see hemimetabolous and holometabolous).

Amine
A class of compound derived from ammonia by replacing the hydrogen molecules with organic radicals. A form in which some types of weed-killers may be prepared, notably MCPA, 2,4-D, 2,4,5-T, CMPP and 2,4-DP. These weed-killers when prepared as amine salts are soluble in water.

Amino acid
The chemical units of which all proteins are composed. There are many in existence but only 20 are common to the proteins of living organisms.

Aminoglycoside
A type of antibiotic which contains a sugar bonded to an amino (NH3) group e.g. streptomycin and tobramycin (inhibit protein synthesis in procaryotic micro-organisms).

Ammonium compounds
Enhance herbicide activity, possibly owing to increased membrane permeability of the leaf tissue.

Amoeba disease
A disease of adult honey bees caused by Malpigh amoeba mellificae.

Amphibolic pathway
A biochemical pathway that serves the dual functions of catabolism and anabolism.

Amphid
Paired chemo-sensory organs located in the anterior region of a nematode (sometimes called lateral organs).

Amphidiploid
A polyploid with a complete set of chromosomes from each parent, usually produced by doubling the chromosome number in the first generation hybrid.

Amphigonic females
Sexual, egg-producing females (= oviparae).

Amphiospore
Urediniospore with thickened walls and capable of hibernation (of rust fungi).

Amphistome
Fluke with the ventral sucker located at the posterior end.

Amphoteric
A compound which has the capacity of behaving either as an acid or base. An amphoteric surface active compound is capable of anionic or cationic behaviour depending on whether it is in an acidic or basic system.

Ampicillin
A semi-synthetic antibiotic produced by chemical modification of penicillin, that inhibits formation of the bacterial cell wall.

Amplification
An increase in the copy number of plasmid in a bacterial cell or culture.

Amylase
Enzyme that breaks down starch.

Anabatic air
A local wind which blows up a slope heated by sunshine. It is a feature which is less common than its converse, the kabatic wind.

Anabolism
The biochemical processes involved in the synthesis of cell constituents from simpler molecules such as sugars and amino acids acquired by animals through ingestion and digestion.

Anaerobic
Living in the absence of free oxygen e.g. anaerobic bacteria. Obligate anaerobes grow only in the absence of oxygen; facultative anaerobes grow either with or without oxygen.

Anaerobic respiration
The oxidation of a substrate using an electron acceptor other than oxygen, such as nitrates, sulphates and carbonates.

Analeptics
Drugs which are medullary stimulants that increase respiration and blood pressure in mammals.

Analogue
In chemistry, a compound similar in structure to another compound but differing in some slight structural detail.

Analysis of variance
An analysis in which the total variation displayed by a set of observations (as measured by the sum of squares of deviations from the mean) is separated into sources attributed to independent variables and pure error.

Analyte
A name given to describe a substance which is being produced in an analytical procedure.

Anamnestic response
A rapid and stronger immune reaction to a second antigen inoculation than the first immunising dose.

Anamorph
The imperfect (asexual) state of a fungus.

Anamorphosis
(= ametabolous development) see ametabola.

Anaplerotic reaction
A reaction that replenishes intermediates that are removed from a biochemical cycle for biosynthesis.

Anapolysis
In nematodes a detachment of a senile proglottid after it has shed its eggs.

Anastomosis
The union of an organ with another resulting in inter-communication of their contents e.g. the union of two fungal hyphae.

Anautogeny
In some diptera the necessity of a blood meal before eggs can develop within the female e.g. mosquitoes.

Androcyclic
In aphids, reproducing by parthogenesis throughout the year, but producing some males to contribute to the sexual phase.

Anecdysis
Successive moults in insects separated by quite long inter-moult phases referred to as 'terminal anecdysis' when a maximal size is reached and there are no further moults (see ecoysis).

Anemophilous
Plants which are pollinated.

Anemotaxis
The ability of certain insects to orient themselves in relation to wind direction.

Aneuploidy
Deviation from the normal number of chromosomes, excluding exact multiples of the normal haploid component.

Angiosperms
Flowering plants (having seeds enclosed in an ovary).

Angle of contact
The angle which the edge of a liquid droplet forms relative to the plane surface of a solid, including plant surfaces, on which the droplet rests.

Angle of repose
The angle formed between the horizontal surface and the side of a natural pile of grain.

Animal unit
A unit represented by one mature cow or horse, or by as many animals as consume an equivalent amount of feed, such as 2 heifers, 2 colts, 7 sheep, 100 laying hens or 5 brood sows.

Anion
An ion that carries a negative charge of electricity that interacts with cations (positive charges) in ionic bonding reactions.

Anionic surfactant
Salt of an organic acid, the structure of which determines surface activity.

Anisogametes
Outwardly dissimilar male and female gametes.

Ankylosed
Consolidation or immobility of a joint.

Annealing
The association by complementary bases of two single strand molecules of a nucleic acid.

Annuals
Plants that complete their life-cycle in one year.

Annulation
A series of transverse depressions on the cuticle of a nematode.

Anoxygenic
Not producing oxygen. Type of photosynthesis carried out by purple and green bacteria in which compounds other than water serve as electron donors, and oxygen is not produced.

Antagonism
Decreased activity or growth arising from the effect of one chemical or organism on another (opposite of synergism). The total response is less than the sum of the independent effects of either applied separately.

Antennae
Paired, sensory, segmented appendages found one on each side of the heads of insects and of some related forms.

Anterior station
Development of a protozoan in the middle or anterior intestinal portions of an insect host, such as the section Salivaria of Trypanosomatidae.

Anthelmintic
A drug or chemical substance used to clear helminths from animals.

Anther
The portion of the flower stamen bearing the pollen grains. When the anthers are ripe they open to release the pollen.

Anther culture
A culture of plant cells derived from excised anthers.

Antheridium
The finger-like male sexual organ of the oomycete fungi.

Anthesis
The period during which flower are open.

Anthocyanescence
Anthocyanescent, the reddish-purple colour in tissues that are normally green - often a plesionecrotic symptom of plant disease caused by an infectious agent, usually appearing in the margins around holonecrotic spots in green leaves.

Anthracnose
A plant disease having characteristic lesions, necrosis and hypoplasia on stems, leaves and fruit. Often caused by certain imperfect fungi e.g. Colletotrichum, Gloeosporium, Kabatiella.

Anti-bacterial
Having action against one or more kinds of bacteria; as a resulting in mortality or inhibition of growth.

Anti-biosis
A toxic or other direct detrimental effect (e.g. on development, reproduction and survival) of one organism upon another. (See also Anti-xenosis). For example the resistance of a plant to insect attack by having a thick cuticle, hairy leaves.

Antibiotic
A chemical compound produced by one micro-organism which inhibits or kills other micro-organisms. In particular it is applied to isolated, purified and chemically modified substances isolated from cultured micro-organisms and employed for therapeutic purposes. Though most widely used to describe anti-bacterials, but scientifically 'antibiotics' include anti-fungal, anti-viral and anti-parasitic compounds of biological origin.

Antibody
A specific protein manufactured by an organism's immune system to counteract the effect of an antigen (a foreign substance). It confers immunity against subsequent infection, in some instances permanently, in others for a limited period (see also antigen).

Antibody titre
Measure of the amount of antibody present, usually given in units per millilitre of serum.

Anti-cholinesterase
An anti-cholinesterase compound prevents the cholinesterase in nerve synapses from splitting the acetylcholines to acetyl and cholines.

Anti-coagulant
A chemical which prevents blood from clotting. It is the active ingredient in some rodenticides.

Anti-codon
A sequence of three nucleic acid bases on transfer RNA molecules which recognises and binds to three corresponding bases (called a codon) of messenger RNA. During protein synthesis this interaction ensures that the amino acid encoded by the codon is added to the growing protein.

Antidote
A practical treatment used in the treatment of poisoning in warm blooded animals e.g. pesticide poisoning.

Anti-drift agent
A compound added to pesticides to reduce the number of fine droplets produced at the spray nozzle.

Anti-feedant
A substance that deters or inhibits feeding by an insect but does not necessarily kill it.

Anti-frothing agent
Material added to prevent frothing of pesticide in the spray tank.

Anti-fungal
A chemical that inhibits or kills fungi.

Antigens
Substances (especially proteins) that are introduced or gain entrance into the blood and that stimulate the immune system to produce antibodies (or, in insects, other protective, lytic, or cidal substances), which react with and render the antigen ineffective.

Antigen challenge
Dose or inoculation with an antigen given to an animal at some time after primary immunisation with that antigen.

Antigenic determinant
Determine' the specificity of the antibody or lymphocyte area(s) on an antigen molecule that bind with antibody or specific receptor sites on the sensitised lymphocyte.

Anti-metabolite
A chemical, structurally similar to biologically active metabolites, that may take their place in a biological reaction, to the detriment of the organism.

Anti-microbial
Inhibits or kills micro-organisms, possibly of several different types.

Anti-oxidant
A chemical used to prevent oxidation, usually a compound which is a good reducing agent.

Antiseptic
An agent that kills or inhibits growth, for use on skin or mucous membranes but not to be used internally.

Anti-serum
The blood serum of a warm-blooded animal that contains antibodies against specific antigen(s).

Anti-serum titre
The highest dilution of an anti-serum that will react with its homologous virus.

Anti-sporulant
Material preventing spore production in fungi without killing vegetative mycelium.

Anti-toxin
An antibody active against a toxin.

Anti-transpirant
A chemical applied directly to a plant that reduces its rate of transpiration or water.

Anti-viral
A chemical that inhibits or kills viruses.

Antixenosis
A resistance mechanism employed (usually by a plant) to deter or prevent pest colonisation. Proposed by Kogan and Ortman (1978) to replace Non-preference; intended to parallel Anti-biosis.

Anvil nozzle
See nozzle ii.

Apex
The tip of a root or shoot containing apical meristem.

Aphagia
Inability to ingest

Apical
Of the top.

Aphicide
An insecticide especially effective against sap-sucking insects particularly aphids.

Apical meristem
The tip of a growing plant root or shoot composed of cells from which subsequent growth develops.

Apical organ
Organ of unknown function at the apex of a cestode's scolex.

Apiculture
Culture and care of bees.

Apimyiasis
Myiasis of the adult honey bee caused by the larvae of Senotainia tricuspis, Rondanioestrus apivorous, and some other fly species.

Aplasia
The complete failure of organs or tissues to develop.

Apnuemone
A substance emitted by a non-living material that evokes a behavioural or physiological reaction that is adaptively favourable to a receiving organism but detrimental to an organism of another species that may be found in or on the non-living material.

Apodeme
Spine-like inward projection of the cuticle in arthropods on which muscle is attached.

Apodous larva
Larva with no legs and with reduced head that requires maternal care or deposition in or on food source. Common in hymenoptera, diptera and some coleoptera.

Apolysis
Disintegration or detachment of (i) a gravid tapeworm segment or (ii) of the hypodermis from the old procuticle in arthropods prior to moulting.

Apomixis
Reproduction which has the superficial appearance of ordinary sexual cycle but actually occurs without fertilisation and/or meiosis hence, the offspring are generally identical to the mother. Usually taken to include parthogenesis.

Apoplast
Non-living matter of the plant including cell walls and xylem, forms a continuous translocation system in the plant body.

Aposymbiotic
Organism separated from its symbiotes i.e. it is symbiote-free and usually refers to mutualistic symbiotes.

Apothecium
An open saucer or disc-shaped sexual fruiting body of the ascomycetes fungi that contains asci on which ascospores are borne. It is a characteristic of the series discomycetes.

Apparent infection rate
Rate of infection, r, calculated in Vanderplank's model of disease development, which takes into account the amount of plant tissue left to be colonised (Parry, 1990).

Appendage
Any structure attached to a part of the body of an organism.

Appetite
A physical craving for food in higher animals expressed as the weight of dry matter consumed as a percentage of live weight.

Application
The act of administering pesticides, or they are placed in such a way that they become available to pests. For herbicides, the following categories: Post-emergence - application of a herbicide after the crop has emerged from the soil; Pre-emergence - application of a herbicide after the crop has been sown or planted but before it has emerged; the term pre-emergence sometimes refers to the weed and it then implies an application of a herbicide before the weeds have come through; Pre-planting - application of a herbicide before the crop is sown or planted; Spot - application made to patches of weed.

Application rate
The total amount of chemical dispensed onto a target surface e.g. a crop, it includes the active ingredient, carrier medium and all additives.

Applied research
The application of science and engineering to the development of new knowledge, new techniques or new products of value (usually economic) to society.

Apportionment
The process of splitting an indirect research cost into smaller parts to charge to various cost centres. Distinguish from cost allocation.

Appresoirum
An enlarged, usually disc-shaped, structure within or at the tip of a hypha of some parasitic fungi from which entry is made into the host.

Appropriation
The decision to set aside money for research and development (R & D), by the government agency, or granting body which controls financial resources for R & D.

Approved product
Proprietary brand of crop protection product (e.g. chemical pesticide) officially approved by Agricultural Departments.

Apterae
Wingless forms, usually referring to wingless parthogenetic female aphids.

Apterous
Wingless stage in the life-cycle of certain insects.

Aquatic plants
Plants that grow in water, of which there are three kinds: submersed, which grows beneath the surface; emersed, which root below but extend above the water e.g. cattails and water lilies; and floaters e.g. water hyacinths.

Arable
Land that is fit for cultivation.

Archaebacteria
One of the three major evolutionary lines of cellular life forms, including the methanogenic, extremely halophilic and thermoacidophilic bacteria.

Area sampling
A method of sampling in which the total area of interest is divided into sub-areas that are then randomly sampled. Each sub-area in the sample is completely enumerated.

Argasid tick
A tick from the family Agrasidae distinguished by the absence of a dorsal shield, e.g. the common fowl tick Argas persicus.

Arid climate
Climate in which annual rainfall is <25 cms, hence requiring irrigation for crop production.

ARIMA models
An acronym for the auto-regressive integrated moving average models used in the Box-Jenkins forecasting procedure.

Arista
A large bristle, located on the dorsal edge of the apical antennal segment in some Diptera.

Arithmetic mean
The arithmetic mean of a set of n measurements x1, x2, x3.... xn is equal to the sum of the measurements divided by n.

Aromatics
Chemicals characterised by the presence of one or more benzene (C6H6) rings - a large class of cyclic organic solvents, many of which are odorous.

Arrestant
A chemical or physical source (light, heat, etc.) that causes an organism to aggregate in contact with it, the mechanism of aggregation being kinetic or having a kinetic component. An arrestant may slow the linear progression of the organism by reducing actual speed of locomotion, or by increasing the turning rate. An arrestant does not attract, but retains organisms once in the vicinity.

Arrhenotoky
That pattern or mode of reproduction in which progeny of both sexes are produced by mated females, the egg when unfertilised producing a viable haploid male and when fertilised producing a viable diploid female, a common condition in Hymenoptera.

Arsenates
A group of inorganic insecticides that are fairly stable, but hydrolyse in water releasing arsenic acid.

Arsenicals
A class of inorganic insecticides containing various forms of arsenic as the basic ingredient. The arsenates are more stable than the arsenites, and considered safer for use on plants.

Arthropods
Invertebrate animals (phylum Arthropoda) with jointed legs and a hard external skeleton, e.g. insects, spiders, crustaceans and millipedes.

Ascaricide
Materials used in the control of any nematode worm of the family Ascaricidae.

Ascaridosis
Infestation with nematodes of the genus Ascaridia.

Ascaroside
Glycoside found in the Ascaris nematode, made of the sugar ascarlyose and a series of secondary monal and diol alcohols.

Ascigerous
Ascus-bearing (perfect) stage of development of an Ascomycete fungi.

Ascites
Accumulation of a clear straw-coloured fluid in the abdominal cavity, causing enlargement of the abdomen.

Ascocarp
Fruiting body (apothecium, cleistothecium or perithecium) of Ascomycete fungi in or on which asci are produced.

Ascogenous hypha
Fungal hyphae arising from the fertilised ascogonium and producing the asci.

Ascomycetes
A class of fungi characterised by endogenous production of spores (asocspores) in the organ of the meiosis (ascus).

Ascospores
Spores (sexually) produced in an ascus in Ascomycete fungi.

Ascus
A sac-like container of ascospores, generally eight in Ascomycete fungi.

Asepsis
The absence of micro-organisms.

Aseptic
Free from infection, brought about by prevention of entry of micro-organisms or by their destruction if already present.

Aseptic technique
Laboratory procedures used in handling cultures, media and equipment that prevent contamination.

Asexual
Having no sex, no division into male and female individuals, no union of gametes in reproduction.

Aspect
Direction which sloping ground faces.

Aspiration
Process of cleaning by moving large volumes of air through a thin layer of grain, to separate light weight particles from the grain.

Asset
Any possession or claim on others which is of value to an individual or organisation.

Assimilate
Products of photosynthesis that are moved in the plant.

Association
Major unit in community ecology, characterised by essential uniformity of species composition.

Asymptote
The point on a graph where a line reaches a plateau; in the growth of a population it is the point at which numerical stability is reached.

Ataxia
Failure of muscular co-ordination through irregularity of muscular action.

Atomise
To reduce a liquid to fine droplets by passing it under pressure through a suitable nozzle, or by applying drops to a spinning disc.

Atomiser
Device for breaking up liquid into fine droplets in a stream of air.

Atonia, atony
In relation to insect diseases it refers to flaccidity, a lack of tone or tension.

ATP
Adenosine triphosphate is a substance present in all living organisms. Its conversion to di- or mono-phosphate liberates energy used for many organic functions including muscular contraction, respiration and 'nitrogen fixation'.

Atropine
A crystalline alkaloid obtained from solansceous plants. It acts as an antidote to organophosphate and carbamate insecticide poisoning in mammals although no antidotal effect is noted on invertebrates.

Atrophy
To waste away, to wither. The decrease in size of a tissue, organ occurs after full development. It is a condition in which the affected cells undergo degenerative and auto-lytic changes, decrease in size, and have a lessened functional capacity.

Attenuated infection
An infection which is not immediately followed by overt disease.

Attenuation
Reduced virulence of a micro-organism, usually brought about by passage through a succession of abnormal hosts. or due to overgrowth of non-virulent strains in laboratory cultures. Attenuated strains are often used as vaccines. Also a process that plays a role in the regulation of enzymes involved in amino acid biosynthesis.

Attractant
Material with odour that attracts insects (lure and kill) used to lure insects to traps, or poison-bait stations. Usually classed as food, oviposition and sex attractants.

Attrition
The wearing away of the surface of a granule, particularly by granule-to-granule interaction.

Augmentation
The practice of rearing and releasing biological control agents such as predators and parasites to enhance natural population levels and to control and maintain the pest population below an economic threshold.

Auscultation
Listening for sounds within the body, for determining abnormality, especially in the lungs.

Autecology
Study of the individual in relation to environmental conditions.

Auto-cidal
The employment of an insect to destroy its own kind or to bring about the self-destruction of the species.

Autochthonous
Native or indigenous (opposite of allochthonous).

Autocide
Self destruction of a pest but usually referred to in the context of the control of a pest by the sterile-male technique.

Autoclave
Apparatus for sterilising by heat under steam pressure.

Auto-correlation
The internal correlation between members of a time series separated by a constant interval of time.

Auto-correlation coefficient
In a time series the auto-correlation coefficient of lag k, rk, measures the amount of correlation between observations that are k periods apart.

Auto-correlation function
A graphical display of the auto-correlation coefficients of a given time series.

Autoecious
Completing life cycle on only one host species (opposite of heteroecious). A term applied to species of rust, all stages of which are produced on a single host.

Autogamy
The fertilisation of a flower by its own pollen.

Auto-immune
Having action against the body (self); a type of disease in which auto-antibodies attack components of the body which produced them.

Auto-infection
Infection of a host by an organism produced within or upon the body of the same individual host i.e. re-infection by a parasite juvenile without its leaving the host.

Autogenous vaccine
A vaccine prepared from a micro-organism obtained from the animal to be vaccinated, as distinct from a vaccine from a stock culture.

Auto-lysis
Spontaneous lysis. The process by which an organism undergoes self-dissolution.

Auto-polyploid
Polyploid with more than two sets of similar chromosomes derived from the same species.

Auto-regression
The generation of a series of observations whereby the value of each observation is partly dependent on the values of those that have immediately preceded it. A regression structure in which lagged response values assume the role of the independent variables.

Autotroph
Organisms which obtain energy from the sun and utilises CO2 as sole source of carbon e.g. plants and some bacteria (contrast with heterotroph).

Autotrophic
Utilising inorganic materials as nutrients; cf. heterotrophic.

Autotrophic nutrition
Feeding that does not require preformed organic molecules as nutritive substances.

Auxin
A plant growth-regulating substance (Indol-3-ylacetic acid) found in plants that stimulates cell elongation in plant tissues.

Auxospore
A spore in diatom algae that leads to reformation of an enlarged vegetative cell.

Auxotroph
A mutant that has a growth factor requirement (contrast with a prototroph).

Auxotrophic
(Of an isolate or strain of a micro-organism), having nutritional requirements additional to those of the 'wild type' , cf. prototrophic.

Available visible radiation
Wavelengths of light between 0.4 µm and 0.7 µm also referred to as 'usable' radiation: equal to ca. 45% of direct solar radiation.

Average rate of return
An investment appraisal method that calculates the annual return on an investment without allowing for the time value of money.

Avermectins
A family of products derived from the fungi Streptomyces avermitilis having toxic activity against arthropods.

Avicide
Lethal agent used to destroy birds or materials used for repelling birds.

Avirulent
Lacking virulence, non-pathogenic, incapable of causing severe disease. Synonymous with non-virulent.

Avirulent gene
A gene that does not contribute to parasitic ability.

Avitaminosis
Vitamin deficiency in the diet. Sometimes the missing vitamin is indicated e.g. 'avitaminosis A'.

Awn
Slender bristle-like projection arising from the back or tip of the glumes and lemmas in some grasses.

Axenic
Pure, uncontaminated e.g. an axenic culture is a pure culture.

Axenic cultivation
The rearing of one or more individuals of a single species in or on a non-living culture medium.

Axial fibrils
Flagella-like structures involved in motility in spirochetes.

Axil
The upper (usually acute) angle between a leaf stalk and the stem from which it branches.

Axil cells
Central cells of a dicyemid mesozoan.

Axillary bud
A bud formed in the upper angle between a twig or a petiole and the stem.

Axis
The main stem of a flower or panicle.

Axoneme
Core of a cilium of flagellum, comprising micro-tubules.

Axostyle
Tube-like organelle in some flagellate protozoa, that extends from the area of the kinetosome to the posterior end, where it often protrudes.

Aziridine
A chemical classification of chemosterilants containing 3-membered rings composed of one nitrogen and two carbon atoms.