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Glossary allele: any of several particular forms of a gene. adverse effects: any change in the information on known risks of pesticide use; must be reported to EPA as part of FIFRA requirements. antitrust: a body of laws making illegal various actions that have the effect of changing prices, allocating sales, or otherwise restraining trade. competition: the interaction between populations in which there is mutual inhibition of each other's growth due to the sharing of common re- source(s). criticalfrequency: the frequency of resistance within a population at which specific strategies should be enacted in order to manage resistance suc- cessfully. It is important to recognize that critical frequencies have not been established for the vast majority of pest/pesticide situations. theme: a local population of closely related organisms. density dependence: situations in which the rate of growth of populations or relative fitness of individuals varies with the standing density of the population. density independence: situations in which the rate of growth of populations or relative fitness of individuals is independent of the density of the population. dtiploi`: individual organisms or cells with two separate sets of genes (chro- mosomes). dominance: situations in which the expression of one allelic form of a gene determines the phenotype of heterozygous individuals and obliterates the expression of recessive alleles of that gene. ecology: the study of the distribution and abundance of organisms and their interactions with their physical and biotic environment. 449

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450 GLOSSARY economic efficacy: "acceptable" pest control from the user's perspective, under field conditions. Many variables influence the user's impression of what is "acceptable." They include effectiveness, cost of the pes- ticide and its alternatives, commodity value, perception of pest severity, injury or public health standards, etc. The fact that a pest population has a verified level and frequency of resistance does not necessarily mean that there has been a loss of economic efficacy, or that use of the pesticide should be discontinued. Conversely, it is possible to have a loss of economic efficacy without resistance (i.e., the introduction of a more effective pesticide, cultivar, or cultural practice; the microbial degradation of the pesticide before it reaches the pest). economic threshold: that pest population density or damage level at which control measures should be taken to prevent economic injury from oc- curring. efflux: passing out, flow out, or pumping out from a cell. epistasis: the nonadditive interactions between genes where the phenotypic expression of alleles of one gene affects the expression of alleles of other genefs). emergency use permits: pesticide-use permits granted under section 18 of FIFRA for specific locations and time periods; granted if unusual pest or pesticide availability conditions arise. genomic shock: an environmental effect that causes movement of genetic elements (e.g., a transposition of genes within a chromosome). genotype: the combination of genes borne by an individual organism. genetically elective component (of migrationJ: the contribution of immi- grants to the genetic makeup of the population in the succeeding gen- eration. fitness: the relative probability of survival and reproductive yield of indi- viduals of a particular genotype. haploid: having only one complete set of chromosomes. heterokaryotic: containing genetically different nuclei (in cells). JR-4: an interregional project supported by USDA and the land-grant col- leges to provide efficacy and safety data necessary for receiving a tol- erance and registration of a pesticide for a minor-use market. linkage disequilibrium: a nonrandom association of alleles at two or more loci. locus: a synonym for gene; the position of a gene on a chromosome (pi. loci). market structure: a description of a group of buyers and sellers in a market that emphasizes number of participants, numbers and types of substitute products, information exchange, and other features affecting level of competition. minor-use: a pesticide market that is small in sales volume because the

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GLOSSARY 451 pesticide is only used on infrequently occurring pests or on pests of a crop that has a small number of acre-applications per year. multinucleate: having two or more nuclei per cell. neolamarckian: the process by which the genotype of individual organisms is changed due to the directed action of the environment. After the French zoologist, J. G. Lamarck (1744-1829), who proposed a theory of evolution operating through the inheritance of acquired characters. phenotype: the physical manifestation of the genes borne by an individual organism. plasmid: short, circular segment of nonchromosomal DNA. plastic: a cytoplasmic organelle concerned with photosynthesis and/or stor- age of food. plastome: the complex of genes in the plastic (also: plastic genome). pleiotropy: multiple phenotypic expressions of a single gene. population biology: the study of the genetic and ecological behavior of populations of organisms. population genetics: the study of genetic diversity and the mechanisms of genetic change (evolution) in populations of organisms. refuge: a place or period of time in which organisms are free from the action of predators or substances that inhibit their growth and repro- duction. relative reproductive rate: the numbers of progeny produced by an indi- vidual of a particular genotype in the course of a generation compared to those produced by other individuals in the population. resistance: the inherited ability in a strain of pest to tolerate doses of toxicant that would prove lethal to a majority of individuals in a normal popu- lation of that species. This definition implies a statistically significant shift in LCX (or LDX) values that are normally established through lab- oratory bioassays. Laboratory documentation of resistance, however, does not necessarily indicate a current or impending loss of economic efficacy in the field. selection: changes in the genetic composition of populations resulting from the differential survival or reproduction of specific genotypes. selective advantage: the extent to which the relative fitness of individuals of a particular genotype exceeds the mean fitness of all genotypes in the population. selective disadvantage: the extent to which the relative fitness of individuals of a particular genotype is less than the mean fitness of all genotypes in the population. thylakoid: flattened membrane sacs within chloroplastids in which chlo- rophyll molecules are incorporated. tubulin: a protein that is a subunit of microtubules, which are found in structures such as the mitotic spindle.

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452 GLOSSARY user fees: taxes or fees that are proportional to use level and are charged to users of public services. variance: the average value of the squared deviations of observations from their mean. It is a measure of the magnitude of variation in a character. In the study of inheritance of continuously distributed characters (Quan- titative Genetics), primary concern is the proportion of the variance in the phenotype ("phenotypic variance") that is due to underlying vari- ation in the genotypes of individuals in the population. additive genetic variance: the proportion of the phenotypic variance that is due to cumulative expression of alleles of the same gene or different genes that are acting independently in the determination of the value of a continuously distributed character, e.g., height. nonadditive genetic variance: the proportion of the phenotypic variance that is due to cumulative expression of alleles of the same gene or different genes that are not independent in their determination of the phenotype, e.g., the contributions of dominance and epistasis. (geneticJ covariance: the average value of the product of the differences between an array of observations taken in pairs and their means. It is used as a measure of the direction and extent a character varies among pairs of individuals and as a measure of how two different characters vary within individuals. As used in Chapter 3, the genetic covariance is the direction and extent of variation in the expression of the same set of genes on two different characters, e.g., tolerance to two different pesticides. Vo~terra principle: The prediction (and observation) that in cases where a prey population is held in check by a predator, the killing of predators and prey (e.g., by the use of pesticides) is likely to result in an increase in the numbers of prey (pests). xenobiotic: foreign chemical (such as a pesticide).