Insect-Pest Management and Control (1969) / Chapter Skim
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ECOLOGICAL BASIS FOR CONTROL
ECOLOGICAL BASIS FOR CONTROL
Pages 48-63
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From page 48... ...
the practical and scientific application of results of long-term studies on the dynamics of insect-pest populations in agricultural ecosystems. THE ECOLOGICAL APPROACH The study of a pest population in a crop ecosystem, in relation to chemical, biological, cultural, physical, or integrated control practices, must be considered in a study of fundamental relationships among host plant, pest population, and related biotic agents, soil, climate, and the management practices of man.
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From page 49... ...
Homogeneity of crop conditions causes the artificiality, while regularity and uniformity of management practices create stability. The host plant and soil-substrate components may sometimes limit the development of pest populations, and some mortality factors, extrinsic and intrinsic to the populations, can limit pest numbers from time to time.
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From page 50... ...
Control studies have often been short-term and concerned mainly with the damaging stage of a pest population, usually the larval stage, and entomologists have therefore become accustomed to think of the stage and not the population as the ultimate unit in pest control. But it is necessary to know not only what effect chemicals, parasites, predators, resistant crop varieties, and any other control measures, singly or combined, have on a given stage, or even on a limited number of stages of a pest population, but also the effect of each on all stages and indirectly on population trend.
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From page 51... ...
To analyze collected data, and to determine their long-term population significance, a series of life tables should be prepared. The life table is a useful numerical aid or device used in the study of insect populations to record in a systematic fashion those facts basic to the age distribution of mortality.
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From page 52... ...
More important, from such a series it is possible to determine biometrically the stage and the factors in the stage that are most responsible for the increases and decreases in pest numbers between and within generations and that warrant further experimental and field investigation. A population-dynamics study also reveals information of immediate practical value: emergence dates and duration of economically important stages, of use in chemical control; the degree of crop injury in proportion to pest density, of use to the grower; and forecasts of densities of pest populations, based on the index of population trend, of use to the grower in planning spray programs.
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From page 53... ...
Species studied were as follows: Species Origin Generations Studied Critical Age Intervals Key Factorsa North America 6 Fruit-tree leaf roller, Archips argyrospilus (Walker) Diamondback moth, Europe Plutella maculipennis (Curtis)
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From page 54... ...
Generations Critical Age Studied Intervals Key Factors" Pupa Parasitism Egg, adult Predation, parasitism Pupa, adult Predation, weather Larva, adult Predation, migration "All the factors except weather are density-dependent; weather is density-independent. KEY REGULATING FACTORS Analyses of life tables for the species listed showed that the critical age interval could occur in any stage of development and that only one or two key mortality factors (or agents)
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From page 55... ...
Since none of the parasites or predators regulating the populations of these pests had been introduced to control them, it is apparent that under certain circumstances resident biotic agents can effectively control major crop pests. The winter moth and birch leaf miner are recent introductions to Canada.
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From page 56... ...
In field populations of the Colorado potato beetle at Ottawa, Canada, intraspecific competition for food was the key factor. Mortality agents are few in potato fields, and in most years the available food supply governs the number of progeny reaching adulthood.
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From page 57... ...
Otherwise, control may be more efficient if based on naturally spreading pathogens directed against the larvae, or on the release of sterile males or sex attractants directed against adults. POSSIBLE REGULATING FACTORS Other mortality factors may be of significance in population regulation; they act in a density-dependent manner against certain crop pests but have not yet been shown to play a critical role.
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From page 58... ...
Stress of competing for limited feeding space led to reduced food consumption, sporadic feeding, excessive dissipation of energy, and eventually to increased susceptibility to disease. Larvae often died from infection that normally would be nonfatal.
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From page 59... ...
Furthermore, variability, the outward evidence of a large gene pool, is also evidence of possible genetic change, and change is inherent in population dynamics. The selective presence of key factors is therefore directly or indirectly connected with the genetics of a species and thus with population change.
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From page 60... ...
As adequate models become available, many approaches should be possible, within mathematical constraints dictated by economics, that would permit the manipulation of key factors regulating population change. For example, it should be possible to lower the mean population density of a pest and reduce the frequency with which it escapes control by natural enemies or threatens its food supply; to determine when applied control measures are necessary and what control will interfere the least with natural enemies and other species; to determine weak spots in the life cycle of a pest or suggest new methods of control; and to integrate
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From page 61... ...
In the spring, chemical control of the bud moth is omitted if winter lows have been -21°F or below, because such lows kill 90 to 95% of the overwintering larvae. However, these lows scarcely affect larvae of the pistol casebearer, which overwinter near the bud moth and receive similar protection, and the omitting of spray applications against the bud moth favors the survival of parasites that control and regulate populations of the casebearer.
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From page 62... ...
In the future, not only will entomologists need to provide quantitative data on key factors, important in the dynamics of pest species and their control, but other workers, such as pesticide chemists, economists, and mathematicians, who are also charged with responsibilities in the development of pest-control measures, will have to provide equally detailed field data. On the basis of all the data, stored in computers for the service of growers, it will be possible to determine, with confidence, interrelationships of key factors from all sources involved in the management of crop-pest species.
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From page 63... ...
1963. Major mortality factors in the population dynamics of the eye-spotted bud moth, the pistol casebearer, the fruit-tree leaf roller, and the European corn borer in Quebec, pp.
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