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L-arginine
A common amino acid of proteins: H₂N-C(=NH)-NH-CH₂-CH₂-CH₂-CH(NH₂)CO₂H.

L-canavanine
A non-protein amino acid closely related to arginine and highly toxic to most insects: H₂N-C(=NH)-NH-O-CH₂-CH₂-CH₂-CH(NH₂)CO₂H.

Label
The written, printed or graphic matter on, or attached to, the pesticide, or the immediate container thereof and the outside container or wrapper of the retail package (if there are any) of the pesticide.

Label (permissive)
In the USA any agricultural chemical has to receive approval of the Department of Agriculture (USDA) for the purpose for which it is intended. Such purpose must be defined and limited by the wording of an agreed label.

Label (radioactive)
When a substance is made incorporating a radioactive isotope of one of its constituent atoms, in order to help trace the movement and chemical reactions of the substance, it is said to carry a (radioactive) label.

Labelling
Supplemental pesticide information that complements the information on the label but is not necessarily attached to or part of the container.

Labile
Liable to change.

Labium
Mouthpart in insects composed of fused second maxillae; homologous to second maxillae of crustaceans.

Labour efficiency variance
The difference between the hours taken and the standard hours allowed for the actual level of production, evaluated at the standard rate per hour.

Labour income (farm)
It is the amount a farm operator receives for a year of labour and management after having paid all business expenses of the farm, including depreciation and making an allowance for a return on capital.

Labour variance
The difference between the actual cost and standard cost of labour that may be due to a difference in labour efficiency or wage rate.

Labrum
Sclerite forming the anterior closure of the mouth in arthropods, specifically, the free lobe overhanging the mouth.

Lachrymation
Secretion and discharge of tears.

Lacquer
Pesticide incorporated into a solvent-based, film-forming composition (lacquer or varnish) to achieve slow release over a lengthy period of time.

Lactation, standard
Usually, milk yielded in 305 days from the date of calving, or from and including the fifth day after calving.

Lacunae
Channels making up the lacunar system in Acanthocephala; also, in developing wings of insects, canals that contain nerves, tracheae and hemolymph.

Lacunar system
System of canals in the body wall of an acanthocephalan, functioning as a circulatory system.

Lag phase
The earliest phase of growth after inoculation, during which the cell number stays constant while cells adjust to the new medium.

Lamella
In mushrooms, one of the thin, spore-bearing gills attached to the underside of the cup.

Lamina
Leaf blade.

Laminae (of the feet)
(a) The convoluted layer of sensitive and vascular tissue between the bone and the horn of the hoof (sensitive laminae); (b) The convoluted layer of horny material in close opposition to the sensitive layer (insensitive laminae).

Laminar boundary layer
The layer immediately next to a fixed boundary in which laminar flow prevails.

Laminar flow
A flow in which the fluid moves smoothly in parallel streamlines; non-turbulent.

Laminar layer
A thin layer of air just beyond the stationary layer at the plant surface, with the character of laminar (non-turbulent) flow.

Laminated structures
Controlled release formulation that consists of several layers of laminated polymeric material wherein the active ingredient is implanted and protectively sealed in an inner reservoir layer between outer plastic protective barrier layers.

Laminitis
Inflammation of the laminae of the foot.

Lance
The rigid tube of a pesticide sprayer, usually metal and trigger mechanism, commonly employed to determine direction of pesticide spray or dust.

Landing
The final process of an act of aerial dispersal; deposition.

Land-races
Stocks of plants selected by farmers on a local basis over many years, which are strongly adapted for local conditions.

Land variety or landrace
A variety developed locally by indigenous people, presumably without benefit of scientific knowledge of plant breeding.

Landscape epidemiology
Approach to epidemiology that employs all ecological aspects of a nidus; by recognising certain physical conditions, the epidemiologist can anticipate whether a disease can be expected to exist.

Lapinised
A vaccine derived from rabbit tissue.

Lapse rate
The decrease of an atmospheric variable with height. Usually refers to temperature unless otherwise specified.

Larva
The growing, caterpillar stage of insects having a complete metamorphosis; the newly hatched six-legged stage of mites and ticks; the life stage of a nematode between the embryo and the adult.

Larval stage
The first stage after leaving the egg, in the development of an insect.

Larval stem nematogen
Early stage in the development of a dicyemid mesozoan.

Larvicide
When an insecticide is used as a control against the larval stage of a pest, it is termed a larvicide. Usually the larval stage in such cases is easier to reach or it is more vulnerable to insecticides than other stages in the life cycle.

Laspeyres index
If the prices of a set of commodities in a base year are p_o1, p_o2, p_o3, ..., and q_o1, q_o2, q_o3, ... are the quantities sold in the base period, and p_n1, p_n2, p_n3, ... are the prices of the same commodities in a given year the Laspeyres index is L = _pnqo _poqo

Last in first out
A stock valuation system where goods are priced when issued to work in progress on the assumption that the last stock received is issued first.

Latent
Concealed. Not clearly visible or defined. Not manifest.

Latent heat
The heat released or absorbed per unit mass by a system when changing phase.

Latent infection
A non-apparent infection in which the pathogen is still present in a non-infective phase, and in which a certain pathogen-host equilibrium is established.

Latent period
The time between infection and sporulation of the pathogen on the host, or time from the start of a virus vector's feeding period until the vector is able to transmit the virus to healthy plants.

Latent virus
A virus that does not induce symptom development in its host. A virus present in a cell, yet not causing any detectable effect.

Latin hypercube sampling
A form of stratified sampling for sensitivity analysis in which the probability distribution of each parameter is divided into n strata or equal probability (1/n) and one sample is taken from each stratum.

Laurer's canal
Usually blind canal extending from the base of the seminal receptacle of a digenetic trematode; it probably represents a vestigial vagina.

Lax
Not compact.

Lay-by application
Application of herbicides after the last cultivation.

Layby pesticide
Pesticide applied with or after the last cultivation of a crop, usually a herbicide.

LC50 or LD50
The lethal concentration or lethal dose of a substance, (usually a pesticide) in air or liquid, for 50% of the test organisms expressed as milligrams (mg) or cubic centimetres (cc, if liquid) per kilogram of body weight. It is also the concentration expressed as parts per million (ppm) or parts per billion (ppb) in the environment (usually water) that kills 50% of the test organisms exposed.

Lcn
The concentration of a toxicant lethal to n% of a test population.

Ldn
The dose of a toxicant lethal to n% of a test population.

LT50
Median lethal time.

Leaching
The movement of a pesticide chemical or other substance downward through soil as a result of water movement.

Leader
A specific amino acid sequence involved in the attenuation process.

Leading indicators
Indicators whose behaviour is believed to be closely correlated with the future behaviour of a variable which is being forecast.

Leaf
The lateral organ of a stem. In grasses it consists of sheath and blade.

Leaf-area index
Total area of leaf per unit area of land.

Leaf blade
The expanded flat portion of a leaf.

Leaf-disk test
A test in which resistance is measured by allowing pests to feed on disks cut from leaves of test plants. Resistance is based on the amount of leaf uneaten after a given test period.

Leaf index

T
he ratio of leaf area produced by plants to the area of the ground on which they are growing.

Leaflet
One part of a compound leaf.

Leaf miner
An insect which lives in and feeds upon the cells between the upper and lower epidermis of a leaf; these being larvae of Agromyzidae (Diptera), Lyonetiidae and Gracillariidae (Lepidoptera) Hispidae (Coleoptera) etc.

Leaf scorch
Leaf necrosis, usually marginal, due to phytotoxicity or nutrient deficiency.

Leaf spot
A self-limiting lesion on a leaf.

Learning effects
Reductions in cost which arise as result of experience in carrying out some activity.

Leghemoglobin
A protein containing heme which functions to bind oxygen in leguminous root nodules.

Legume
Plant family Leguminoseae, and its members, which contains root nodules and is capable of symbiotic nitrogen fixation with bacteria of the genus Rhizobium e.g. alfalfa, clover, beans, peas.

Leishman-Donovan body
Amastigote in the Trypanosmatidae; also known as an L-D body.

Leishmaniasis
Structure occurring in pairs attached to the inner posterior margin of the neck of an acanthocephalan, extending into the trunk cavity. Its function is unknown.

Lemma
In grasses, the lower bract that with the palea encloses the flower.

Lenticel
A pore in a stem, root, some fruits and bark which permits the inward and outward passages of gases.

Lesion
Any break in the epidermis of a plant or a localised, diseased or disordered tissue.

Leslie matrix
A matrix giving the survival and fecundity by age of females in a population. Used to project the future of the population from an initial state.

Lethal concentration
A term used to express the concentration of toxicant required to give a percentage kill, usually in twenty four hours, of test subjects in an air or water medium. Concentrations are expressed as milligrams or grams per litre of air, or as parts per million in water.

Lethal dose
(LD) A term used to express the amount of a substance that will produce a given mortality within a given time (usually twenty four hours) under specific conditions. This terminology is applied to toxicants that are administered directly to the organism.

Lethal time
A term used to express the time required for a defined dose of toxicant to produce a given mortality level in a test organism or group of organisms.

Leucopenia
A reduction in the number of white corpuscles in the blood.

Leukocidin
A substance able to destroy phagocytes.

Leukocyte
A white blood cell, usually a phagocyte.

Level-of-effort
A general term for the amount of work required to accomplish a R&D task, project or programme. It is usually equated with the amount of money required, labour needs, materials or other resources required to do the job.

Levels
A statistical term to describe the possible conditions or states of the independent variables.

Levels of a factor
The settings of values of a factor in an experiment.

Levels of biologic organisation or integration
The stages or steps in the hierarchy from molecule to biosphere.

Ley
The name given to an annual, or short-period perennial, grass crop, usually introduced into an otherwise arable rotation.

L form
A wall-less procaryote derived from an organism with a wall.

Level-of-effort
A general term for the amount of work required to accomplish a R&D task, project or programme. It is usually equated with the amount of money required, labour needs, materials or other resources required to do the job.

Liberation
The first process in the act of aerial dispersal, in which the fungal spore is freed from its sporophore, pustule etc., also called take-off.

Lichen
A regular association of an alga or cyanobacterium with a fungus, usually leading to the formation of a plant-like structure.

Liebeg's law
The assumption that the effect on a process of several factors is the minimum of the effect caused by each of the individual factors.

Life cycle
The complete succession of changes undergone by an organism during its life. A new cycle occurs withe the initiation of an identical succession of changes.

Life cycle costing
The division of a project's life cycle into seven costing stages: specification, design, make or buy, installation, start up, operating and terminal stage.

Life table
Tabulation presenting complete data on the mortality schedule of a population e.g. the age-specific survival of cohorts of individuals in relation to their age or stage of development.

Light attenuation
The observed physical phenomenon that light levels are reduced through a water column or canopy with depth.

Lignification
Impregnation of cell walls with lignin.

Lignified
Cell walls strengthened and thickened with aromatic compounds. Found in woody tissues.

Lignin
A complex amorphous substance that, in association with cellulose, causes the thickening of xylem vessels and plant cell walls and thereby forms wood or woody parts.

Ligninase
An enzyme that breaks down lignin.

Lignituber
Deposits of lignin, cellulose and pectin produced by a plant around a fungal hypha attempting to penetrate a cell. Constitutes part of a defence mechanism by host.

Ligule
The appendage or ring of hairs on the inside of grass leaves where the sheath and blade join.

Limiting factor
A factor that restricts the growth of a business. The limiting factor may be sales, finance, skilled labour or materials.

Limit value
The limit at or below which Member States of the European Community must set their environmental quality standards and emission standards. These limits are set by Community Directives.

Line
Host plants of uniform appearance, the stability of which is maintained by selection.

Line functions
A relationship between two or more units in an organisation which is based principally on differences of authority.

Linear correlation
A measure of the strength of the linear relationship between two variables y and x that is independent of their respective scales of measurement. Linear correlation is commonly measured by the coefficient of correlation.

Linear programming
A mathematical, computer-based farm planning technique which can be used to determine the combination of activities which maximises total 'profit' or minimises costs subject to a number of constraints.

Linear statistical model
An equation of the form y = ß0 + ß1x1 + ß2x2 + .... + ßkxk + _ that relates a single dependent variable y to a set of independent variables x1, x2, ..., xk, where ß0, ß1, ... ßk are unknown parameters and _ is a random error.

Lipase
An enzyme that breaks fat into glycerin and fatty acids.

Lipid
Group of organic compounds which are esters of fatty acids and which are characterised by being insoluble in water but soluble in many organic solvents.

Lipophilic
'Fat loving' used to describe a molecule or group of atoms having an affinity for oil - rather than water solubility.

Lipophilic moiety
That portion which is attracted to lipids.

Lipophobic
Used as opposite of lipophilic.

Lipopolysaccharide
Complex lipid structure containing unusual sugars and fatty acids found in many gram-negative bacteria and constituting the chemical structure of the outer layer.

Liquidity
The ease with which assets can be converted into cash e.g. animals and jewellery are liquid assets, land less so.

Lister
An implement used for furrowing land. It frequently has a planting attachment.

Listeriosis
Infection with micro-organisms of the genus Listeria.

Lithotroph
An organism that can obtain its energy from oxidation of inorganic compounds. Equivalent to chemolithotroph.

Liver nodule
A small node, or aggregation of cells within the liver.

Livestock feed budget
A budget comparing feed requirements of livestock with the feed available.

Livestock gross income
The value of livestock production in the form of animals and produce, adjusted for inventory changes.

Live weight
The weight of a live animal. With ruminants this is difficult to obtain accurately because of the large amounts of fodder and water consumed daily. Daily variations may be extreme and of the order of 70 kg in adults. To be comparable, weighing should be carried out at the same time of day on each occasion and preferably outside grazing peaks. and should be repeated on three successive days.

Loam
A soil made up of sand, silt and clay particles in such amounts as to exhibit properties of sand and clay in about equal proportions.

Local infection
An infection affecting a limited part of a plant.

Local invasion
That involving only a localised area of the plant.

Local lesion
A localised spot produced on a leaf upon mechanical inoculation with a virus.

Local lesion assay
A quantitative estimation of the infectivity of a preparation of a pathogen, e.g. a suspension of bacteria and viruses, from the number of lesions produced in inoculated leaves of a host on which small, distinct lesions are formed.

Local variable
A variable that appears only within a simulation subroutine.

Loculi
Shallow, sucker-like depressions in an adhesive organ of a flatworm.

Locus
(Loci). The position of a particular gene on a chromosome.

Lodging
The condition of a plant that has been beaten to the ground or otherwise damaged so that it cannot stand upright, especially cereals damaged by wind and rain.

Lodicules
The pair of organs at the base of the ovary of a grass floret that swell and force open the lemma and palea during anthesis.

Logarithmic reproduction curve
A reproduction curve with logarithmic axes.

Logarithmic sprayer
See sprayer iv. A device for spraying a pesticide at a steadily decreasing rate of application.

Logistic equation
dN = rmN (K-N) dt ( K ) where rm = intrinsic rate of natural increase, k = carrying capacity, N = population size and t = time. A differential equation used to describe single species population growth over time, which is dominated by an intrinsic growth rate and a saturation level or carrying capacity.

Logistic-type model
Type of optimum-yield model in which the yield is predicted from an overall descriptive function of population growth without a separate analysis of the components of mortality, recruitment and growth; contrast with dynamic-pool model.

Log-normal distribution
A continuous probability (frequency) distribution of species abundances in which the X axis is expressed on a logarithmic scale; X axis is (log) number of individuals represented in sample, Y axis is number of species.

Longevity end-point
The storage time after which a virus in a crude sap preparation loses its infectivity. Usually determined at 0° or 20°C.

Long-term toxicity study
A study in which animals are observed during the whole life span (or the major part of the life span) and in which exposure to a test material takes place over the whole observation time or a substantial part thereof. Chronic toxicity study is sometimes used as a synonym for 'long-term toxicity study'.

Looper
A caterpillar of the family Geometridae, with only one pair of abdominal prolegs (in addition to the terminal claspers) and which moves by looping its body.

Lophotricous
Having a tuft of polar flagella.

Lorsch disease
A rickettsial disease of the larvae of June beetles species of Melolontha and of Amphimallon (beetles), as well as other related scarab larvae caused by Rickettsiella melolonthae.

Loss, direct
The loss of quantity or quality of produce and of yielding capacity caused directly by pest or disease attack i.e. the pest is attacking the harvestable product e.g. grain rather than plant foliage.

Loss equivalent area
The additional area of land needed to produce a yield equivalent to that lost by pest and disease attack. Also the extra land which would become available if losses were prevented.

Loss, indirect
The loss sustained by the social and economic sphere surrounding the producer and indirectly due to pest or disease attack.

Loss, potential
A loss that may be expected to occur in the absence of control measures.

Loss, primary
A reduction in yield quality and quantity resulting in loss of income and/or an increase in production costs.

Loss rate
General term to describe the rate of removal of organisms from a population by death and emigration.

Loss, secondary
The loss in yielding capacity of future crops.

Losses of crop product
Crop products may be lost from the food chain at any or all of the periods between planting and preparation for immediate consumption. Three general periods have been identified. (a) Pre-harvest losses occur before the harvesting process begins and may by due to such factors as insects, weeds or diseases afflicting the crop. (b) Harvest losses occur during the harvesting process and may be due for example to shattering and shedding of the grain from the ears to the ground. (c) Post-harvest losses occur during the post-harvest period and may also be caused by pest attack.

Lot
Part or all of a consignment that may comprise part of, all of or more than one batch.

Louse fly
Member of the dipteran family Hippoboscidae.

Lowest-observed-effect level
The lowest dose of a substance which causes changes distinguishable from those observed in normal (control) animals.

Low volume spray
Concentrate spray, applied uniformly over the crop, but not to the point of run-off.

Luciferase
The enzyme that catalyses light formation in luminescent bacteria.

Lumen
The cavity or channel within a tube or tubular organ.

Luminescence
Production of light.

Lunules
Small, sucker-like discs on the anterior margin of some copepods in the family Caligida, functioning as organs of adhesion.

Luxation
Dislocation, usually of a joint.

Lycophora
Ten-hooked larva that hatches from the egg of a cestodarian tapeworm; also called a decacanth.

Lye
Water alkalised with wood-wash or other alkaline solution for washing.

Lymphadenitis
Inflammation of lymph nodes.

Lymphocyte
A white blood cell involved in antibody formation or cellular immune response; B-lymphocytes make antibody; T-lymphocytes are involved in cell-mediated immunity.

Lymphokine
Any one of several kinds of effector molecules released by T lymphocytes when antigen to which the lymphocyte is sensitised binds to the cell surface.

Lymph varices
Dilated lymph ducts.

Lyophilic
Oil or organic solvent attracting.

Lyophilisation
Long-term preservation of micro-organisms or tissues by quick freezing at low temperatures and desiccation under high vacuum.

Lyophilised
Freeze-dried. Processed by rapid freezing and dehydration under high vacuum, causing the product so treated to become more stable.

Lyophobic
Oil or organic solvent repelling.

Lysin
An antibody that produces lysis.

Lysis
A breakdown or dissolution of cells by enzyme or viruses resulting in loss of cell contents.

Lysogenic
Describing a bacterium that contains a temperate bacteriophage integrated into the cell DNA.

Lysogeny
The hereditary ability to produce virus.

Lysosome
A cell organelle containing digestive enzymes.

Lysozyme
An enzyme in body fluids, active in host defence; able to kill invading organisms by digesting the bacterial cell wall.