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Glossary of Terms

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Mutual interference constant. A measure of the rate of decrease in searching efficiency as parasite density increases.

Macartney (bottle)
A small bottle about 5 cm high with wide mouth.

Prefix (Greek) meaning 'large'.

A thick-walled structure of multi-cellular origin in the cellular slime moulds, which may be involved in sexual reproduction.

Large, quiescent, 'female' anisogamete.

Cell giving rise to a macro-gamete.

Particle size range from 2,000 to 6,000 µm.

A large molecule formed from the connection of a number of small molecules. A polymer. Informational macro-molecules play a role in transfer of genetic information e.g.proteins, polysaccharides and nucleic acids.

A large phagocytic cell found in connective tissues, especially in areas of inflammation; includes wandering cells in the blood and lymph and histocytes in the reticuloendothelial system.

Macrophage migration inhibitory factor
Lymphokine released by sensitised lymphocytes that tends to inhibit factor migration of macrophages in the immediate vicinity, thus contributing to accumulation of larger members of macrophages close to the site of MIF release.

Large, or long-winged insect.

That which may be seen with the un-aided eye, or without the aid of a high-powered lens or microscope.

Macroscopic pathology
The study of tissue changes which are visible to the naked eye.

Small spots, flecks or stains on or in an organ, or on the skin of an animal.

Referring to maculae.

Diptera (fly) larva.

Major gene resistance
Genetic resistance to disease based on one or a few genes (synonymous with vertical resistance).

Major resistance genes
Confer a high level of resistance

Metal pipe assembly underground or on soil surface, conveying spray fluid from pump to hoses.

Maintenance requirement
The food required by an animal to maintain its body weight or prevent catabolism of its own tissues.

Malaya disease
A lethal disease of larvae of the Indian rhinoceros beetle, Oryctes rhinoceros, caused by a virus.

Male sterility
In flowering plants when the pollen is absent or non-functional.

A cancerous growth. (A mass of cells showing both uncontrolled growth and the tendency to invade and destroy surrounding tissues).

A type of tumour which invades surrounding tissue and is no longer controlled by the organism on which it is growing; contrast with benign.

Ventral, serrated projection on the ventral surface of a male nematode of the family Syphaciidae; its function is unknown.

Mammalian toxicity
Toxicity of crop-protection products to mammals often expressed as mg per kg body weight required for median lethal dose.

Managed cost centre
A responsibility centre where the manager is responsible for giving the best level of service while keeping within his budget.

Management accounting
The provision of detailed cost and income data to facilitate the role of managers in financial planning, controlling and decision making.

Management information system
Any planned system of collecting, storing, processing and presenting information to management so that effective decision-making and control can take place.

Managerial dis-economies of scale
Increases in cost per unit at larger scales of output attributable to the loss of control associated with attempting to manage larger organisations.

Man-day of labour
The amount of accomplishment expected of a farm worker in a 10 hour day, using adequate equipment and operating at the average rate of performance.

Appendages in Crustacea, in Insecta; primarily used for feeding (biting or chewing).

Mann-Whitney U test
A non-parametric test proposed by Wilcoxon for comparing two population distributions by first ordering the combined observations from the samples selected from each population and then summing the ranks of the observations from the samples. The Mann-Whitney U test uses a function of the rank sums as its test statistic.

Either gross or net profit as a percentage of sales value.

Economists' word for 'extra' or 'added'. The principle of marginality refers to the profit-maximising level of operation where the marginal revenue from production equals the marginal cost of production.

Marginal bodies
Sensory pits or short tentacles between the marginal loculi of the opisthaptor of an aspidogastrean trematode.

Marginal cost
The extra cost incurred of adding one more unit of input to the production process.

Marginal costing
A system of costing used for decision making which is based on the analysis of costs into fixed and variable categories. Only the variable costs are used in product costs and stock values. The system has gained wide acceptance for price/output decision making.

Marginal product (or revenue)
The change in output (or income) arising from using an extra unit of an input.

Marginal product of labour
The additional output arising from the use of an additional unit of labour.

Margin of safety
The difference between the current level of activity and that needed to break-even, expressed as a percentage of the current level.

An additive to make spray deposits conspicuous or as an aid to indicate correct position of swath.

Market pricing
The determination of a product's price based on market conditions and marketing criteria.

Markov chain
A stochastic model having discrete states in which the probability of being in any state at any time depends only on the state at the previous time and on the probability transition matrix.

A percentage addition to costs to cover overheads and/or profit.

A crumbling deposit of calcium carbonate mixed with clay and other impurities.

Nasopharyngeal blockage by a parasite. Also called halzoun.

Masked symptoms
Virus-induced plant symptoms that are absent under certain environmental conditions but appear when the host is exposed to certain conditions of light and temperature.

Maslin (meslin)
A mixture of growing grains, such as oats and barley, or the product milled from it.

Mass culture
The propagation in an insectary of very large numbers of a biological control agent, often on a continuous basis over a period of months or years.

Masseter (muscle)
The muscle connecting the upper and lower jaws and covering the angle of the lower jaw.

Mass median diameter (M.M.D.)
Figure dividing total volume of spray into two equal parts: one half of the mass of spray is contained in droplets of smaller diameter than M.M.D., and the other half is contained in droplets of larger diameter.

Mass selection
A system of breeding in which seed from individuals selected on the basis of phenotype is composited and used to grow the next generation.

Master budget
The overall budget built up from the detailed functional budgets and expressed in a budgeted profit and loss account, a budgeted balance sheet and a budgeted funds flow statement.

Axoneme of a cilium or flagellum together with its basal fibrils and organelles; also called a kinetid.

Inflammation of the udders of a cow resulting from bacterial infection.

Mating type
A group within a species classified on the basis of its mating behaviour. Fungi often have genes that control mating type at 1, 2 or even 3 loci and there may be multiple alleles at each locus. In heterothallic species, individuals must differ in mating type alleles at each locus for mating to occur.

Material price variance
The difference in cost between actual and standard unit purchase prices, multiplied by the actual quantity purchased.

Materials variance
The difference between the actual cost and standard cost of materials that may be due to a difference in price or usage.

Material yield variance
The value of the abnormal gain or loss in process, in excess of the standard allowance.

Mathematical model
A model using algebraic expressions to represent relationships within the system.

Any substance on which a fungus lives.

Maturation phase
In virus infections, a phase or period following the eclipse period, during which infective particles are completed.

A term applied to cells or tissues which have completed their differentiation.

Mature stock unit
(Also known as livestock unit). A means of computing the grazing load of a herd by comparing each age group, using a cow as unity, thus: Adult bull 1.2 Growing cattle over 2 years old 1 Cow 1.0 Yearling 1-2 years old 0.5 Cow in-milk 1.1 Weaners 6-9 months old 0.25 Calves under 6 months old 0.125 This may be refined as 500 kg cow, 1.0; then indigenous cows are taken as 0.8 or 0.9 depending on LW, and similarly with other ages of indigenous cattle.

Maurer's clefts
Blotches on the surface of an erythrocyte infected with Plasmodium falciparum.

Fifth pair of appendages in Crustacea, primarily for feeding; homologous to labium in insects; maxillae of insects are third pair of head appendages, homologous to maxillules of Crustacea.

One or more pairs of head appendages originating posterior to maxillae in Crustacea; usually function in feeding but sometimes adapted for other functions, such as prehension, in parasitic forms.

Fourth pair of appendages in Crustacae, primarily feeding in function; homologous to maxillae in insects.

The value of a stimulus above which no response occurs.

Maximum residue limit
The maximum concentration of a residue that is legally permitted on or in a food or food commodity at a specified stage in the harvesting, storage, transport, marketing or preparation of the food, up to the final point of consumption. The concentration is expressed in milligrams of residue per kilogram of food (mg/kg) (formerly in parts per million [ppm] which is numerically the same).

An area of land devoted to the production of forage, mainly perennial, that is harvested for hay.

Mean absolute deviation (MAD)
A measure of accuracy of a forecasting model calculated by averaging the absolute values of the forecast errors: MAD = 1 _n|yt - yt| n t=1 Mean absolute percentage error (MAPE) A measure of forecast accuracy calculated by error averaging the absolute values of the percent errors made by the forecasting model: MAPE = 1 _n|yt - yt|(100%) n t=1| yt |

Mean square error (MSE)
In forecasting the MSE measures forecasting accuracy by averaging the squares of the forecast errors: MSE - 1 _ (yt - yt)² n

Measured daywork
A group incentive payment scheme where a fixed sum is paid above the basic rate if agreed performance targets are achieved.

Mechanical inoculation
A method of experimentally inoculating a plant with a virus through transfer of sap from a virus-infected plant to a healthy plant. Of plant viruses, a method of experimentally transmitting the pathogen from plant to plant; juice from diseased plants is rubbed on test-plant leaves that usually have been dusted with Carborundum or some other abrasive material.

Mechanical transmission
Used to describe artificial transmission of a virus in which an infectious preparations is rubbed onto a test plant. May also occur in the field when virus is transmitted from one plant to another by leaves rubbing or root contact.

The median of a set of n measurements x1, x2, x3, ... xn is the value x that falls in the middle when the measurements are arranged in order of magnitude.

Median effective concentration
EC50 The concentration of toxicant or intensity of other stimulus which produces some selected response in one half of a test population.

Median effective dose
The dose which will produce a response in half the test subjects; the chief characteristic of this dose is that it is an indirect measure of the mean tolerance of a batch of test subjects. Its symbol is ED50; the median lethal dose (LD50) is a special case, in which death is the response. ED50 The statistically derived single dose of a substance that can be expected to cause a defined non-lethal effect in 50% of a given population of organisms under a defined set of experimental conditions.

Median effective time
The time at which a response occurs in half the test subjects after exposure to a chemical or pathogenic (including toxicological) stimulus; its symbol is ET50; the median survival time (ST50) is a special case, in which death is the response.

Median lethal concentration
LC50 The concentration of a toxicant lethal to one half of a test population.

Median lethal dose (LD50)
A more restricted concept of the median effective dose. The statistically derived single dose of a chemical that can be expected to cause death in 50% of a given population of organisms under a defined set of experimental conditions. This figure has often been used to classify and compare toxicity among chemicals but its value for this purpose is doubtful. One commonly used classification of this kind is as follows: Category LD50 Orally to Rat mg kg-1body weight Very toxic <25 toxic >25 to 200 Harmful >200 to 2,000

Median lethal time
In a time-dependent assay procedure, this is the period of exposure to a chemical or pathogen (including toxicological) which will produce death in half the test subjects; the length of exposure is a direct measure of dosage, and an increase in the period of exposure results in an increase in uptake and true dose in the same ratio. Its symbol is LT50.

Median survival time
A restricted concept of median effective time; the time at which death occurs in half the test subjects after exposure to a chemical or pathogen (including toxicological). Its symbol is ST50.

Mediastinal (lymph nodes)
The lymph nodes situated between the lungs and below the trachea and bronchi. They drain the lungs, heart and parts of adjacent organs.

Medium size brokens
Broken pieces of the rice grain, between ¼ - ½ kernel size.

Medium volume
See spray x.

Central part of an organ.

Flabby, distended colon caused by chronic Chagas' disease.

Distended oesophagus caused by chronic Chagas' disease.

Mehlis' glands
Unicellular mucous and serous glands surrounding the ootype of a flatworm.

The process of division of sexual cells in which the number of chromosomes in each nucleus is reduced to half the normal number found in normal somatic cells. When two sexual cells fuse, each contributes its half of the chromosomes. The resulting embryo contains the full chromosome complement. Cells with half the chromosomes are called haploids, while those with the full complement are diploids.

A disease of queen honey bees, characterised by discoloration of the egg cells and trophocytes, which turn from yellow-brown to black.

Mellow soil
A porous, softly granular soil that can be worked easily without becoming compacted.

A thin, soft tissue. Thin film.

Short, transverse rows of cilia, fused at their bases, serving to move food particles toward the oral groove of a protozoan.

Membrane filter method
A method for counting organisms, especially in dilute samples; the liquid sample is passed through a membrane filter, which is placed on agar medium to permit the organisms to grow and be counted.

The property of Markov chains of having the future depend only on the present state and not directly on any past states.

Covering membranes e.g. the tough membrane covering the brain and spinal cord.

Inflammation of the meninges.

A medium used for growing organisms in which the chemical identity of certain, but not all, of the absolutely essential molecules has been established.

The undifferentiated, mitotically active tissues of plants. The meristems at the tips of roots and shoots are referred to as apical meristems (King & Stansfield, 1990).

Meristem culture
A cell culture developed from a small portion of the meristem (growing tip) tissue of a plant. Either a stem shoot or root meristem can be used.

Merit rating
A method of evaluating personnel usually linked to an incentive payment scheme. Points are awarded against a list of 'desirable' personal characteristics to derive an individual's rating.

Meromictic lake
A lake in which complete mixing to the bottom does not occur. Generally has a permanently anaerobic bottom layer.

The daughter cells derived by multiple fission (schizogony) from an original cell, in asexual reproduction of protozoa.

Mesh size
Number of grids per inch through which described particles will pass, e.g. 60-mesh granules.

Moderately moist habitat.

Prefix (Greek) meaning 'in the middle'.

The middle layer of the pericarp or fruit wall which is often fleshy or succulent.

Juvenile stage of the digenetic trematode Alaria; it is an un-encysted form between the cercaria and the metacercaria.

Organism living in the temperature range around that of warm-blooded animals i.e. between 18-25°C and 37°C.

Layer of chloroplast-containing cells between the epidermal layers of a leaf. Soft wood. The leaf parenchyma cells between epidermal layers.

A plant that thrives under medium moisture conditions. Most crop plants are mesophytes.

The middle section of the thorax of an insect that bears the top wings and the middle pair of legs.

Messenger RNA (m-RNA)
m-RNA carries the genetic code for a protein from the DNA to the ribosomes where the code is read and the protein manufactured. A chain of ribonucleotides that codes for a specific protein.

Metabolic activation
The biotransformation of relatively inert chemicals to biologically reactive metabolites.

Metabolic age
Age related to the proportion of mature weight achieved: calculated as age multiplied by mature weight raised to the 0.27th power.

Metabolic intermediate
A compound produced during a series of enzymatic reactions, which is altered by the subsequent enzymatic reactions.

Metabolic size
Metabolism is proportional to body surface. This is extremely difficult to determine; as a substitute, comparisons may be made on the basis of an animal's 'metabolic size' or live weight to the power of 0.73, i.e. LW0.73.

The total sum of the chemical and physical changes constantly taking place in living matter. All biochemical reactions in a cell by which organisms utilise nutritive material to build living matter and structural components, or break down cellular material into simple substances to perform special functions.

A product of metabolism - formed by biochemical interaction upon a substance introduced into the normal system of an organism, including animal, plant and micro-organism.

Metabolite pesticide
A breakdown product of a pesticide resulting from biological, chemical or physical action on the pesticide within a living organism.

Metabolisable energy
May be estimated on the basis of one gram total digestible nutrient has 4.4 kcal of digestible energy and that 82% of digestible energy is available as metabolisable energy. Thus metabolisable energy values may be converted to digestible energy by multiplying by 1.22.

Stage between the cercaria and adult in the life cycle of most digentic trematodes; usually encysted and quiescent.

Developmental stage of a cestode after metamorphosis of the oncosphere.

Metachromatic granule
Reserve of inorganic phosphate stored within the cell and stainable by basic dyes; also called volutin.

Merozoite developed from a cryptozoite.

Stage in the life cycle of a parasite that is infective to its definitive host.

Cystic stage of a parasite that is infective to a host.

Metal shadowing
A technique used to prepare viruses for electron microscopy, in which the virus particles are exposed to the vapour of a heavy metal such as gold or platinum. Now replaced by the negative contrast staining method.

One of the segments in a metameric animal.

Division of the body along the anteroposterior axis into a serial succession of segments, each of which contains identical or similar representatives of all the organ systems of the body; primitively in arthropods, including, externally, a pair of appendages and, internally, a pair of nerve ganglia, a pair of nephridia, a pair of gonads, paired blood vessels and nerves, and a portion of the digestive and muscular systems.

The series of changes through which an insect passes in its growth from the egg through the larva and pupa to the adult. Defined as complete when the pupa is inactive and does not feed and incomplete when there is no pupa and where the nymph is active and feeds.

Later naupliar larvae of some crustaceans, i.e. after several naupliar stages but before another larval type or pre-adult in developmental sequence.

Changed condition of a structure or organ; hyperplastic class of symptoms characterised by overdevelopment other than that due to hypertrophy or hyperplasia, examples: abnormal starch accumulation, virescence.

Portion of the podosoma that bears the third and fourth pairs of legs of a tick or mite.

Metapolar cells
Posterior tier of cells in the calotte of a dicyemid mesozoan.

Portion of the body anterior to the major point of body flexion in may copepods; usually includes cepahlothorax and several free thoracic segments.

The transfer of pathogenic micro-organisms to parts of the body remote from the original foci of infection or the transfer of malignant tumour cells from one organ or part to another, where they grow and form secondary tumours or a secondary tumour.

To form metastases.

Metastatic (lesion)
A lesion which has been established in an organ by metastasis from another organ.

The last division of the thorax of insects, bearing the second pair of wings and the third pair of legs (see mesothorax).

The multi-cellular members of the animal kingdom, as opposed to the protozoa, or unicellular members.

A type of archabacterium which is capable of producing methane gas.

Method of least squares
A technique for the estimation of the coefficients in a regression equation that chooses as the regression coefficients the values that minimise the sum of squares of the deviations of the observed values of y from those predicted.

An organism that can grow on organic compounds containing no carbon-carbon bonds.

Muscular, distended termination of the uterus of a digenetic trematode.

mg/kg (milligrams per kilogram)
Measurement used to designate the amount of toxicant per kilogram of body weight of a test organism required to produce a designated effect, usually the amount necessary to kill 50% of the test animals.

A hyperbolic curve form originally applied to the rate of nutrient uptake as a function of nutrient concentration, but also applied to a variety of other relationships.

Prefix (Greek) meaning 'small', 'minute'.

A species of bacteria which grow best with only a small amount of oxygen.

An aerobic organism which is poisoned by oxygen when it is present in normal amounts (such as in air), but which requires reduced oxygen levels for growth.

Micro-biological assay
A procedure to measure small concentrations of vitamins or other nutrients by measuring bacterial growth.

The combined micro-flora and micro-fauna of an organism; or, the micro-flora or micro-fauna considered separately.

Generally a 10-3m to 10-9m diameter particle, composed of a core material and an outer wall. The outer wall isolates the core material from the environment and protects it from environmental degradation and interaction with other materials. The core materials are designed to be released in a controlled fashion.

Elements occurring in small amounts.

A procedure in pesticide formulation that applies a uniformly thin polymeric coating around small solid particles, droplets of liquid, or dispersions of solids in liquids; the size of the resulting capsules ranges from a fraction of a micrometer to several thousand micrometers (Bakan, 1975). Capsules greater than 2,000-3,000 µm are called macro capsules.

The environmental conditions in the immediate microscopic surroundings of a microbial cell; often these conditions are different from the larger environment in which the organism grows.

A term sometimes used to designate forced feeding of small volumes of solutions or suspensions to insects and other small animals.

A bundle of cellulose molecule chains arranged in crystalline and in amorphous regions.

First-stage juvenile of any filariid nematode that is ovoviparous; usually found in the blood or tissue fluids of the definitive host.

Slender, active, 'male' anisogamete.

Granular formulation of a pesticide with a particle size range of 100 to 600 µm.

A device for injecting measured, minute amounts of fluids onto or into insects during toxicological studies.

Slender, convoluted bodies that join a duct system with the rhoptries, opening at the tip of a sporozoite or merozoite.

Intermediate larval stages of the isopod suborder Epicaridae, parasitic on free-living copepods.

A mineral nutrient element required in minute amounts by plants.

Temporary parasite.

Cell that gives rise to micro-gametes.

A small knot of thick-walled vegetative hyphal cells produced as a resting structure by some fungi.

This term is sometimes used to designate the smaller organism, or micro-organism, of a symbiotic association.

Tubes that are the structural entity for eucaryotic flagella, have a role in maintaining cell shape, and function as mitotic spindle fibres.

Microbial control
That part of biological control concerned with controlling insects (or other organisms) by the use of micro-organisms (including viruses); pathogens may exert their control by means of their invasive properties, by toxins, enzymes and other substances.

Microbial insecticide
A pathogenic micro-organism or its products (toxins etc.) that is applied in the same way as a conventional pesticide to control a pest population (sometimes referred to as an inundative release). The terms 'microbial pesticide', 'biotic insecticide' and 'microbial control product' are also used.

Microbial leaching
The extraction of minerals from low-grade ores by action of bacteria, especially Thiobacillus ferrooxidans.

Microbial persistence
A phenomenon characterised by the continued presence of a pathogenic micro-organism within the host in the absence of overt disease but following an episode of overt disease.

Microbial pesticides
Living micro-organisms, such as fungi, bacteria, viruses, protozoa and nematodes, as well as metabolites produced by micro-organisms that are used in pest control.

An experimental eco-system, usually small in scale and with controlled environmental conditions.

A myxospore of a myxobacterium enclosed in a hard slime capsule.

One millionth of a metre, or 106 (abbreviated µm), the unit for measuring microbes. Formerly called micron.

A unit of measurement equal to one-thousandth of a millimetre. µm, 1/1,000 millimetre or 1/25,000 inch.

An opening through which the pollen tube passes, also pore in the oocyst of some coccidia and in the egg of an insect.

Very small; can be seen only with the aid of a microscope.

Minute projections of the tegument of a cestode.

Middle coccygeal (artery)
A small artery sunk between two muscles and running along the middle of the ventral surface of the tail. It is convenient to use in taking the pulse rate of cattle and other large ruminants, especially when they can only be approached when in a crush or similarly restrained. Arterial blood samples may also be taken from this artery.

Middle lamella
A layer of pectic substances on which the other cell wall materials are deposited. Forms the 'cement' between plant cells, except in woody tissues, where pectin is replaced by lignin.

In heteroecious aphids, alate parthogenetic females which migrate between the primary and secondary host.

Migrating from plant to plant.

A fungous disease characterised by the appearance of a white, mycelial growth and spores on the surface of infected plant parts.

Military nodules
Small numerous nodules clustered together in a bunch. Characteristic of a very common tubercular lesion in the lungs.

Milky disease
Any of a group of diseases beetle of scarabaeid larvae, caused by species of the genus Bacillus; type A milky disease of the white grub of the Japanese beetle (Polillia japonica) is caused by Bacillus popilliae, whereas type B milky disease (marked by extensive formation of blood clots, impairment of circulation, and gangrene of the appendages) is caused by Bacillus lentimorbus.

Milled rice
Rice obtained from paddy after the husk and bran have been removed.

mµ A unit of length equal to 1/1,000 of a micron.

Mills period
Period of apple leaf wetness satisfying requirements for light infection by Venturia inaequalis ascospores.

The conversion of organically bound elements into inorganic forms, which are then available for metabolism.

A substance, one of the elements of nature, which either in inorganic or organic combinations with other elements is essential in the nutrition or physiological function of the body.

Deep holes or tunnels in plant parts caused by burrowing insects or their larvae.

Minimax decision
In a decision analysis the minimax decision is the decision to select the action whose maximum opportunity loss is the smallest.

That value of a stimulus below which no response occurs.

Minimum efficient scale
(MES) The minimum scale of production at which all known scale economies have been achieved.

Minimum inhibitory concentration
The lowest concentration of an antibiotic that inhibits growth of a test organism.

Minimum tillage
A production system in which soil cultivation is kept to the minimum necessary for crop establishment and growth, thereby reducing labour and fuel costs and damage to soil structure.

Minor resistance genes
Confer a low level of resistance but it is thought that they may, when aggregated in a single genotype, give a high level of resistance that is durable.

The free swimming larva of a trematode which penetrates the body of its snail host and develops further to become a cercaria.

Two or more liquids which, when combined together, form a uniform stable mixture, a term applied to oils that have an agent added to the oil that makes it easy to dilute with water and remain as a mixture without separation.

Miscible oil
See emulsifiable concentrate.

Mist spray
See spray xi.

Mist spraying
Method in which concentrated spray is atomised into an air stream.

Air-carrier sprayer producing fine spray.

Preferably acaricide, pesticide for killing mites.

Minute bodies in the cytoplasm of a cell which are responsible for respiration and specialised reactions. The enzymes they carry catalyse the biochemical processes of cell respiration and the anabolic conversion of simple substances into compounds which store chemical energy.

The normal process of the division of somatic cells (i.e. non-sexual cell) in which the chromosomes are duplicated longitudinally to give two daughter nuclei each having a chromosome complement equal to that of the original nucleus (parent).

Mixed function oxidases
Oxidising enzymes which are involved in the metabolism of many foreign compounds giving products of different toxicity from the parent compound.

Mixed infection
Concurrent infection by two or more pathogenic micro-organisms.

Mixed layer
The layer of air (usually sub-inversion) within which pollutants are mixed by turbulence.

An organism able to assimilate organic compounds as carbon sources while using inorganic compounds as electron donors.

Median lethal dose; same as LD50.

Modal length
The length that occurs most frequently in a population of virus particles.

The mode of a set of measurements x1, x2, x3, ... xn is the value of x that occurs with the greatest frequency. The mode is not necessarily unique.

Mode of action
A term used to describe the way or method by which a pesticide may alter or adversely affect physiological or biochemical events in an organism resulting in a toxic effect, usually ending in death.

A simplified representation of a system (which may be expressed in word, diagrammatic or mathematical terms). The use of model in a scientific context implies (1) that the thing being represented cannot be directly observed, or, in some cases, directly manipulated, and (2) that the model itself is in some degree hypothetical and subject to validation. A model can consist of statements in ordinary language, but models of complex systems often utilise graphic or mathematical symbols. An advantage of mathematical models is that much of the labour of testing them can be performed by computers.

Model, crop loss
A mathematical method used to describe the relationship between yield reduction and intensity of harmful organisms.

Model, multiple point
Prediction model providing estimates of crop loss from multiple assessments of one or more disease progress/pest development curve.

Modification enzyme
The counterpart of a restriction enzyme. It chemically modifies some of the bases so that the restriction enzyme can no longer cut the DNA.

Modulus function
The value of the function, modulus (x,m), is the remainder when x is divided by the modulus m.

In chemistry this term refers to a part of a molecule; loosely about a half; a part.

Moisture content
Amount of water in the grain. Expressed as percentage based on wet or dry i.e. Moisture content = weight of moisture in grain sample x 100 (wet basis) total weight of the grain sample a) Wet basis (wb) The moisture content is defined as the ratio of the weight of water to the total weight of dry matter and water. This is the most commonly used method in agriculture. b) Dry basis (db) The moisture content is defined as the ratio of the weight of water to the dry-matter weight. This method is normally used in scientific laboratory work. In agriculture it is traditional to use wet-basis moisture contents. Where moisture contents are expressed without an indication of wb or db, it may be assumed that the moisture contents are on a wet basis.

A gram molecular weight of a substance.

Molecular biology
The study of the major macro-molecules of living cells, including DNA, RNA, protein and others.

A chemical used to kill or control snails and slugs some of which are intermediate hosts of parasites of medical importance to man.

Taxonomic classification of bacteria as a separate kingdom.

The process of observing project progress and resource utilisation, and anticipating deviations from planned expectations.

Monitoring programme
A sampling design for an ecosystem in an area subject to some impact with the objective of detecting a significant change in target biota if one occurs.

Having or consisting of a single carpal.

Flowering and fruiting once then dying.

Produced from a single genetically pure cell type; often referring to antibody produced from a hybridoma cell made from a single type of B cell.

Monoclonal antibody
An extremely pure antibody derived from a single clone of an antibody-producing cell. Invading pathogens, viral or bacterial, carry a large number of different antigens each capable of stimulating the host's immune system to generate a corresponding antibody. A single spleen cell exposed to a specific antigen can be fused with a myeloma (cancer) cell. The resultant fused cell, called a hybridoma, continually produces an antibody specifically directed against the antigen. It will therefore seek out and identify the specific antigen. Hybridomas can be cloned and cultured to produce quantities of the pure 'monoclonal antibody'. Because of its specificity each monoclonal antibody may be used for diagnostic or therapeutic purposes. Most research and development has employed mouse antibodies grown in the peritoneal cavity of immuno-suppressed mice. Specific diagnostic tools which allow the rapid detection of individual proteins produced by the cells.

Any seed plant (angiosperm) having a single cotyledon or seed leaf. Leaves are mostly parallel veined e.g. cereals, grasses, rushes and sedges and various weeds

Refers to plants that have separate male and female flowers on the same plant, synonym of autoecious; also to rusts that have all stages of their life cycle on a single species of plant.

Monoecious aphid
An aphid that spends its complete life-cycle on a single plant species.

The growing of a single crop species continuously or in successive seasons over a wide area.

The processes of a single infection cycle consisting of deposition, infection, colonisation, symptom expression, sporulation, take-off, and flight. One that is restricted to a single generation per cropping season.

Mating of an animal with only one member of the opposite sex.

Single stomached.

Normally relating to resistance or controlled by a single gene.

Containing one nucleus.

A small unit that is repeated many times in the formation of a polymer.

An infectious disease caused by viruses, which is usually transmitted by direct contact, such as kissing, and is associated with an abnormal increase in phagocytic cells (monocytes).

An animal that feeds on or utilises a single species of host plant.

Monospecific pastures
Pastures composed of a single species.

Fluke that lacks a ventral sucker.

Positing but one essential element; in classifications, defining groups on the basis of a single key character.

Monotonic function
A function that never increases (or never decreases) as the independent variable increases.

The state of having single polar flagellum.

Living within a single host during a parasite's life cycle.

Tapeworm whose 'strobila' consists of a single unit.


Involving the use of random numbers in a computer programme or simulation model to obtain approximate solutions to some problem.

Monte-Carlo technique
A simulation model that can be used to make allowance for risk in a project's cash flows. The principle is based on the study of chance using combinations of numbers. Tables are constructed for different factors and probabilities and simulation trials are run to produce a frequency distribution.

The condition of being diseased. The morbidity rate is the proportion of sick to healthy animals.

A condition exhibited by an organism just prior to death or recovery, especially when poisoned. An organism in this state manifests abnormal reactions to stimuli.

Study of the form, structure, architecture and development of organisms.

That branch of pathology dealing with the morbid changes occurring in the structure of cells, tissues and organs, as distinguished from physio-pathology.

The term commonly used to denote death or kill of organisms treated with toxic chemicals.

Mortality rate
Death rate; the number of deaths per unit population during a given period of time.

Symptom of certain viral diseases of plants characterised by intermingled patches of normal and light green or yellowish colour.

Mosaic disease
A disease characterised by variegated patterns of green and yellow on the foliage of plants caused by certain viruses.

Most probable number
A method for counting organisms, using liquid media; also a statistical expression providing a measure of cell number in a population.

Moth fly
Member of the dipteran sub-family Psychodinae, family Psychodidae.

The property of movement of a cell under its own power.

An pattern of indistinct light and dark areas on plant tissue that is symptomatic of many virus diseases.

A fungus which grows as hyphae interwoven into an extensive mycelium, with aerial hyphae and conidiospores usually on decaying matter of on plant surfaces.

The shedding or casting off of the cuticle in insects.

Moving average forecast model
A forecast computed by averaging together the past k values observed from a time series.

To cut with a mower, sickle or scythe.

Messenger RNA, a molecule which is synthesised from a DNA template by the enzyme RNA polymerase.

Decomposed organic material, usually 20 to 50% organic matter mixed with mineral matter, dark in colour, and accumulated under poor drainage conditions.

Consisting of mucous and pus.

Apical anchoring device on an acephaline gregarine protozoan.

Mucous membrane
Interior epithelial layers across which mucous flows; not actually a membrane, but a layer of epithelial cells.

Material used to form a covering over the soil, usually to prevent evaporation of soil moisture.

Multi-component virus
A virus whose genome is divided into two or more parts, each part being separately encapsidated. Hence two or more components are needed to initiate an infection. Note that this is different to a multi-partite genome where components may be enclosed in a single particle.

Multi-generation study
A toxicity test in which at least three generations of the test organism are exposed to the chemical being assessed. Exposure is usually continuous.

Normally relating to resistance controlled by more than one gene.

A crop grown from a mixture of seed of almost genetically identical breeding lines (isogenic) which have all agronomic characters in common, but differ in major gene resistance, thereby confronting pests with a mixture of host gene-types.

Multi-line variety
Different lines of a cultivar mixed to form a composite variety, the lines being equal in agronomic characters but varying in quality and/or quantity of resistance; a modern technique to increase intra-specific diversity of a crop.

Multi-nomial experiment
An experiment consisting of n identical and independent trials, each of which results in one of k possible outcomes with p1, p2,..., pk where _pi = 1 and 0 _ pi _. The experimenter is interested in n1, n2, ..., nk, the number of trials resulting in each of the k outcomes.

Multiple alleles
A series of alleles or alternative forms of a gene.

Multiple genes
Two or more independent pairs of genes which produce complementary or cumulative effects upon a single character of the phenotype.

Multiple parasitism
The situation in which more than one parasitoid species occurs simultaneously in or on the body of the host.

Multiple regression analysis
A regression analysis in which the mean value of a dependent variable y is assumed to be related to a set of independent variables x1, x2, ...., xk by an expression of the form E(y|x1, x2, ..., xk) = ß0 + ß1x1 + ß2x2 + ßkxk

Refers to an organism that has several generations during a single season; contrast with uni-voltine.

A dried, diseased fruit.

A term used generally with reference to mycoses of insects caused by the fruiting of muscardine fungi on the exterior of the insect.

A fleshy fruiting body of a fungus, especially of a basidiomycete of the family Agaricaceae.

Substance causing genes in an organism to mutate or change.

The production of mutations. Any chemical which causes mutations is said to be mutagenic. Some mutagenic chemicals are also carcinogenic.

The quality of causing birth defects in future generations.

An individual having an abnormal structure, property or behaviour in which it differs distinctly from the parent organism from which it was derived. This is an inheritable change (a change in the sequence or chemistry of the purine or pyrimidine bases contained in DNA molecules) and may be caused or induced by high energy irradiation or by certain chemical substances.

A suddenly occurring heritable change in DNA. Such mutations may be brought about by chemical or physical agents (mutagens) e.g. U.V. radiation. An abrupt appearance of a new characteristic in an individual as a result of an accidental change in genes or chromosomes. 1. The process by which a gene undergoes structural change. 2. A modified gene resulting from mutation (King & Stansfield, 1990).

Mutual interference
As natural enemies aggregate in patches of high prey density it is increasingly likely that they will encounter each other while searching for prey. The effects of such encounters between searching natural enemies are classified under the general heading of mutual interference (see m).

A symbiotic relationship between two different species in which both benefit from the association and cannot live separately.

Mutually exclusive events
Two events A and B are said to be mutually exclusive if the event AB contains no sample points.

The vegetative structure of a fungus, made up of the filamentous hyphae.

The presence of a fungus or some of its stages in the circulating blood of an animal.

A cell containing intra-cellular mutualistic and commensalistic micro-symbiotes; one of many cells making up the mycetome.

In various invertebrate animals, the structure or organ which houses symbiotes; the cells making up the mycetome and containing the symbiotes are known as mycetocytes.

Plant pathogenic fungi which are applied pre- or post-emergence for the control of weeds.

Mycolic acid
Long-chained, branched fatty acids characteristic of members of the genus Mycobacterium.

The study of fungi.

Feeding on fungi.

A micro-organism intermediate in size between viruses and bacteria possessing many virus-like properties and not visible with a light microscope.

Literally, 'fungus root'. A symbiotic association of roots with a fungus which may form a layer outside the root (ectotrophic) or within the outer tissues (endotrophic).

An infection by a parasitic fungus, or a disease caused by the action of a mycotoxin.

Toxin produced by fungus; formed when grains or some other products become mouldy.

Refers to green plants having mycorrhizae.

A virus that infects fungi.

A condition in animals deriving from infestation by parasitic flies.

Inflammation of the muscular wall of the heart.

Myoneural junction
The site of transmission of an impulse from a nerve to a muscle.

A naked cell capable of amoeboid movement; characteristic of the vegetative phase of myxomycetes and such plasmoidophoromycetes as Plasmodiophora brassicae.

The slime moulds, a class of fungi characterised by amoeboid vegetative protoplasts, plasmodia, and by brightly coloured spore-bearing capilitia.

A division of fungi, to which belong the myxomycetes and the plasmodiophoromycetes, the 'primitive fungi'.

The resting cell of a myxobacterium contained within a fruiting body.

Apical stalked, sucker-like organ on the scolex of some tetraphyllidaen cestodes.