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Objective function
The function that is to be optimised in an optimisation problem.

Objectives
Very specific, highly technical and frequently quantitative statements of the expected results of R & D project tasks.

Obligate
Refers to an organism that is restricted to a particular set of environmental conditions, without which it cannot survive.

Obligate parasite
A parasite which is obliged to live in or on its host, as distinct from a facultative parasite, which has the ability to live on or in the host or away from it.

Obligate predator
Predator that is restricted to eating a single species of prey.

Obligate saprophyte
Organisms that can live only on non-living matter.

Obligate symbiont
Organism that is physiologically dependent on establishing a symbiotic relationship with another.

Obligate weed
A weed never found in the wild stage, but growing only in association with man.

Obtect pupa
A pupa in which the appendages are more or less glued to the body surface.

Occasional pests
A pest generally under natural control, that exceeds the economic injury level only sporadically or in localised areas.

Occluded
Blocked off, closed tight; term used to describe viruses in which the virions are contained in a dense protein crystal, large enough to visible in the light microscope.

Occult virus
A special phase of some viruses, characteristic of latent infections, in which the pathogenic agent is presumed to differ from the infective phase, and in which virions cannot be detected.

Occupational hygiene
The applied science concerned with the recognition, evaluation and control of chemicals, physical and biological factors arising in or from the work-place which may affect the health or well-being of those at work or in the community.

Ocelli
Small, single visual units located on the heads of spiders and many insects.

Ocular (lesion)
Pertaining to the eye.

Odontostyle
The feeding stylet of a nematode (eelworm).

Odum diagram
A model diagram oriented toward energy transactions.

Oedema
(Edema) Intumescence or blister formation due to an increase in inter-cellular water, as in leaves.

Oesophagus
The part of the alimentary canal that connects the mouth with the intestinal tract.

Oestrogenic
Used of substances inducing oestrous or sexual heat.

Oestrous
The recurrent restricted period of sexual receptivity in female animals, marked by intense sexual urge.

Off-line quality control
Statistical techniques, especially experimental design methods, used in quality control to improve the design of a product.

Oil dispersible powder
A powder formulation of a pesticides dispersed in an organic liquid and applied as a suspension.

Oil miscible liquid
A stable liquid suspension of active ingredient that is diluted in an organic liquid for application.

Oil phase
The non-aqueous liquid portion of an emulsion which consists of water insoluble pesticidal agents with or without surfactants or solvents.

Olfactometer
A device for measuring behaviour as affected by odours or vapours (sense of smell) e.g. a Y tube which passes a stream of air over the test material for comparison with a similar blank stream of air. Measurements may be made of attraction of test organisms or non-attraction.

Oligidic
Pertaining to a medium (used for growing organisms) consisting wholly or largely of crude materials, in which no molecule (other than water) has been established as an absolute nutritional requirement.

Olignucleotide
A nucleic acid composed of several or many nucleotides bonded together.

Oligochaetes
Any class or order (Oligochaeta) of heraphroditic terrestrial or aquatic annelids lacking a specialised head; includes earthworms.

Oligogenic
Governed by a few genes e.g. oligogenic host resistance.

Oligonucleotide
A very short length of a nucleic acid molecule.

Oligophagous
Animals or parasites that restrict feeding to a few host species, often they are a group of closely related species.

Oligopod larva
Usual larva in Coleoptera and Neuroptera, with well-developed head and thoracic legs.

Oligosaccharide
A compound consisting of relatively few (2-10) mono-saccharide units, which, upon complete acid hydrolysis, yields only simple sugars.

Oligotrophic
Describing a body of water in which nutrients are in low supply.

Omasum
The third of the four compartments of the ruminant stomach.

Omnivores
Animals that feed on material of both plant and animal origin.

Onchocerciasis
Infection with Onchocerca a genus of filarial worms, some members of which encyst in the tissues of animals.

Onchocercoma
Subcutaneous nodule containing masses of the nematode Onchocerca volvulus.

Oncogene
A gene which codes for a product which causes transformation of a normal cell into a cancer cell. Oncogenes are slightly changed equivalents of normal cellular genes called proto-oncogenes. The viral version is designated by the prefix v, the cellular version by the prefix c.

Oncogenic
Tending to cause tumours (not necessarily cancers) in tissue.

Oncomiracidium
Ciliated larva of a mono-genetic trematode.

One-tailed statistical test
A statistical test of a hypothesis in which the rejection region is wholly located at one end of the distribution of the test statistic.

On-farm 'half-field' comparison
A method based on grower's collaboration, which aims to demonstrate and quantify suspected yield loss factors by protecting a portion of the field against pest and disease attack and leaving the rest untreated.

On-farm research
A problem orientated approach to agricultural research that begins by diagnosing the conditions, practices and problems of particular groups of farmers. Once the problems are identified a research programme is designed to address them. A key part of any such programme is conducting experiments on farmers fields under farmers conditions and management. Those experiments are then evaluated using criteria that are important to farmers, and the results are used to make recommendations (Tripp & Woolley, 1989).

Onisciform larva
A flattened platyform larvae, like a wood-louse in appearance.

On-line quality control
The use of statistical methods, especially control charts, to monitor the consistency of manufactured products.

Onset, of an epidemic
The time when disease is first easily visible in the field; roughly equivalent to the perception threshold when disease severity (x) equals 0.001 to 0.05, depending on disease and observer; not to be confused with the beginning of an epidemic or first lesion in a population. Visibility threshold

Oocysts
A part of the sporogony phase of protozoa which occurs after macro-gametes have been fertilised by micro-gametes in the intermediate host. The subsequent multiplication of cells produces an oocyst, each cell then becoming a sporozoite which is subsequently injected into the final host.

Oocyst residuum
Cytoplasmic material not incorporated into the sporcyst within an oocyst; seen as an amphorous mass with an oocyst.

Oogenotop
Female genital complex of a flatworm, including oviduce, ootype, Mehlis' glands, common vitelline duct and upper uterus.

Oogonium
In fungi, the female reproductive structure of such oomycetes as Pythium spp. and Phytophthora spp. containing one or more gametes.

Ookinete
Motile, elongate zygote of a Plasmodium or related organism.

Oomycete
A fungus that produces oospores. An order of the phycomycetes.

Oosphere
An unfertilised egg; a female gamete.

O÷spore
A resting spore produced by sexual reproduction in the oomycetes e.g. downy mildew and related fungi.

Oostegites
Modified thoracic epipods in females of the crustacean super-order Peracarida; they form a pouch for brooding embryos.

Ootheca
Egg packet secreted by some insects; may be covered with sclerotin.

Ootype
Expansion of the flatworm female duct, surrounded by Mehlis' glands, where, in some flatworms, ducts from a seminal receptacle and vitelline reservoir join.

Open pollination
Pollination without control so that the male parent is not known.

Open system
A system which exchanges matter with the surroundings, it may also exchange energy with the surroundings.

Operating budget
The plan for expenditure of money for all costs associated with actually running a R & D programme.

Operating characteristic curve
A plot of the probability of accepting the null hypothesis when some alternative is true (the probability of a type II error) against various possible values of the alternative hypothesis.

Operating costs
Variable costs plus overhead (fixed) costs.

Operating profit
Gross income minus variable and operating overhead costs.

Operations
The actual conduct of the research and development activity in a organisation; a term used to distinguish the act of conducting R & D from that of planning or policy.

Operator
A specific region of the DNA at the initial end of the gene, where the repressor protein attaches and blocks mRNA synthesis.

Operculum
The lid or cover-like specialisation of a parasite eggshell through which the larva escapes.

Operon
A group of genes which function as a collective unit. A cluster of genes whose expression is controlled by a single operator.

Opisthaptor
Posterior attachment organ of a mono-genetic trematode.

Opisthomastigote
A form of Trypanosomatidae with the kinetoplast at the posterior end; the flagellum runs through a long reservoir to emerge at the anterior; no undulating membrane e.g. Herpetomonas.

Opisthosoma
Portion of the body posterior to the legs in a tick or mite.

Opisthotonus
A form of spasm in which the muscles of the back are violently contracted causing the head and tail to come nearer each other and the abdomen to be protruded forward.

Opportunism
Guileful behaviour designed to take account of asymmetries of information between parties to a transaction.

Opportunistic pathogen
An organism that only causes disease when host resistance is abnormally low.

Opportunity cost (or cost)
The opportunity cost of a farm management decision is the amount of money which is given up by choosing one alternative rather than another.

Opsonisation
Modification of the surface characteristics of an invading particle or organism by binding with antibody or a non-specific molecule in such a way to increase susceptibility of the cell to phagocytosis.

Optical density
A means of expressing numerically the turbidity of a suspension, such as a bacterial culture. (As cell number increases so does optical density).

Optimal decision
In a decision analysis the optimal decision to select the action that maximises the decision maker's objective.

Optimal foraging
A theory that asserts that an organism chooses its food such as to maximise its energy intake per unit time.

Optimal pricing
A calculation that relates output to price to determine a price and output level that will maximise profit.

Optimisation
Maximising or minimising according to some objectives. Refers to a series of techniques for choosing system controls such as to achieve the best possible performance under these objectives.

Optimum
Most favourable. That value of a stimulus at which response is greatest.

Optimum yield
Amount of material that can be removed from a population that will maximise biomass (or numbers, or profit, or any other type of 'optimum') on a sustained basis.

Oral toxicity
The toxicity of a compound when ingested. Usually expressed as number of milligrams of chemical per kilogram of body weight when given orally in a single dose that kills 50% of the animals. The smaller the number, the greater the toxicity.

Orchitis
Inflammation of the testes.

Order
For a differential equation the highest derivative in the equation; for a numerical approximation solution to a differential equation the order denotes the accuracy in terms of the highest power of the time interval _ included in the approximation.

Ordination
Process by which plant or animal communities are ordered along a gradient.

Organ culture
The maintenance or growth of organ primordia or the whole or parts of an organ in vitro in a way which may allow differentiation and preservation of the architecture and/or function.

Organelles
Organised micro-structures within cell cytoplasm, having specialised biochemical functions, e.g. chloroplasts, mitochandria. A structure found within an individual cell which has a specific function e.g. mitochondion for cellular respiration.

Organic compound
A compound other than carbon dioxide (CO2) which contains one or more carbon atoms; when there is more than one carbon atom, carbon atoms are usually bonded to each other.

Organic matter
The fraction of the soil composed of carbon based materials often thought to be primarily responsible for the sorption of most chemicals (Lyman et al, 1982). Measured as a percentage of dry weight.

Organisation chart
A two-dimensional, rectilinear diagram of the roles, responsibilities and functional relationships among units in a research programme.

Organisational slack
Unnecessarily high costs due to lack of tight control.

Organising
Using the characteristics of structure to establish technical and authority relationships among units of a research programme.

Organochlorine insecticide
One of the many chlorinated hydrocarbon insecticides e.g. DDT, dieldrin, chlordane, BHC, Lindane etc.

Organophosphate
Class of insecticides derived from phosphoric acid esters that act as inhibitors of the enzyme cholinesterase.

Organotins
A classification of acaricides and fungicides containing tin as an active constituent of the molecule.

Oriental sore
Disease caused by Leishmania tropica. Also called Jericho boil, Delhi boil, Aleppo boil, or cutaneouos leishmaniasis.

Orifice (or nozzle)
Velocity at which pesticide spray leaves nozzle velocity orifice.

Oroya fever
Clinical form of Carrion's disease, caused by the bacterium Bartonella baciliformis and transmitted by sand flies.

Oscillations
Regular cyclic population changes which are the consequence of delayed dependent factors, and have peaks in the generation curve which are 5 or more generations apart.

Osmophilic
Requiring an environment with increased solute concentration.

Osmosis
Diffusion of substances through a cell wall or other membrane.

Osteomalacia
A softening of the bones, so that they become flexible and brittle chiefly due to depletion of the calcium/phosphorous reserves which are stored in bones.

Ostile
A pore or opening in a fungal body (a perithecium or a pycnidium) through which spores are discharged.

Otoacariasis
Infestation of the external ear canal by ticks or mites.

Outbreak area
In locusts the area that can produce swarms that may then move into the invasion area; outbreak area may be permanently inhabitable by locusts.

Outcross
Cross-pollination, usually by natural means, with plants differing in genetic constitution.

Outer layer
A thin membrane lying outside the peptidoglycan layer in gram-negative bacteria; consists of lipopolysaccharide attached to the peptidoglycan layer.

Outlier
One or more observations in a data set that are distant in value from the main body of the set. Outliers may come from a separate population or may result from sampling or recording errors.

Output
The goods or products e.g. food and fibre which come from a production process.

Output variables
Variables that are not of major importance in running a model but that are produced as model output, e.g. producing the value of some state variable in different units than in the model for comparison with field data.

Ovacide
Pesticide specifically active in the control of the egg stage of numerous insects.

Ovary
In plants, that part of the pistil, usually the enlarged base, which contains the ovules and eventually becomes the fruit. The female reproductive structure that produces or contains the egg.

Overall application
Pesticides, applied uniformly over the whole area (as opposed to band application).

Over-dispersion
Ecological term meaning non-random dispersion of individuals in a habitat, e.g. when a minority of host individuals will bear a majority of parasites.

Overhead
The collection of indirect costs of R & D for a research organisation. Generally a cost that is not usually charged direct to a cost unit and tends to be fixed in relation to output.

Overhead efficiency variance
This variance arises in standard costing when overheads are recovered on the basis of time as opposed to units of product. It is the difference between the standard overhead cost allowed for the actual production level achieved, and the standard overhead cost for the actual time taken.

Overhead variance
The difference between the actual cost and the budgeted cost of overheads.

Overhead (fixed) costs
Costs which do not vary greatly as the level of production or mix of activities changes, but which must be met each year.

Over-seed
Broadcasting seeds on the soil surface.

Overtop application
Application over the top of transplanted or growing plants, such as aerial application or raised boom spray of ground rigs; a broadcast or banded application above the plant canopy.

Ovicapt
Sphincter on the oviduct of a flatworm.

Ovicide
A pesticide toxicant for insect or mite eggs. Usually restricted to action on eggs of phytophagous mites e.g. red spider mite. The word is almost universally accepted in this sense, but in classical terminology it should mean 'sheep (Latin, ovis)-killer' and that an egg-killer should be 'ovacide'.

Oviduct
The portion of the female reproductive system between the ovary and the uterus.

Oviparae
Sexual females which mate with males and lay fertilised eggs.

Oviparous
Producing young from an egg which is hatched and live young produced from it inside the body.

Oviposition
The act of laying or depositing eggs.

Ovipositor
The ovipositor is an extensible tube on the abdomen of a female insect which is used to place eggs in a suitable location in plants, the ground or in other organisms. Often capable of great drilling power. Hence oviposition - the act of egg-placing.

Ovisac
External sac attached to the somite that bears openings of gonoducts in females of many Copepoda; fertilised eggs pass into the ovisacs for embryonation.

Ovovitellarium
Mixed mass of ova and vitelline cells; found in the monogenean genus Gyrodactylus and in a few tapeworms.

Ovoviviparous
Producing living young from eggs that hatch within the female's body.

Ovule
An immature seed which develops into a seed after fertilisation.

Ox
A castrated male. This word is normally used when the animal is kept for draught purposes while 'steer' is used if kept for meat.

Oxidation
Combining with oxygen. Burning is oxidation. A chemical reaction in which oxygen combines with another substance or in which hydrogen atoms or electrons are removed from a substance.

Oxidation-reduction (redox) reaction
A coupled pair of reactions, in which one compound becomes oxidised, while another becomes reduced and takes up electrons released in the oxidation reaction.

Oxidative phosphorylation
The utilisation of energy released by the oxidative reactions of respiration to form high energy ATP bonds.

Oxygenic
Oxygen-producing; a type of photosynthesis carried out by plants, algae and cyanobacteria in which the electron donor, water, is split and oxygen is produced.

Oxygenic photosynthesis
Use of light energy to synthesis ATP and NADPH by non-cyclic photophosphorylation with the production of O2 from water.

Oxytetracycline
An antibiotic drug produced from a species of mould used widely in veterinary medicine and marketed under numerous trade names.

Oxytocin
A hormone secreted by the pituitary gland and released into the blood stream which induces 'let-down' of milk. Adrenaline, another hormone, is secreted when an animal is frightened, cancelling out the oxytocin effect and so stopping let-down.

Ozone
A highly reactive form of oxygen that in relatively high concentrations may injure plants.