Abstract
Three different types of model have been used in the past to forecast aphid outbreaks or to understand their causes. These can be considered as empirical, synoptic (sensulato), and functional. Empirical models are results of statistical analyses of observed population data, yielding regression equations relating aphid incidence to various other factors. For example, Vickerman (1978) found that summer aphid numbers on cereals in the UK were negatively related to spring temperatures, an apparent anomaly attributed to the positive influence of spring temperatures on natural enemy populations. Synoptic or lumped-parameter models do not distinguish age-classes and generally consist of one or two equations broadly reflecting the underlying biological processes involved. Whalon & Smilowitz (1979) developed such a model to predict the rate of build-up of green peach aphid (Myzus persicae Linnaeus) populations on potatoes in Pennsylvania. The aim was to provide advance warning of the need to spray and for the model to be readily implemented on the microcomputers already used by many growers. The single equation is based on the biologically realistic assumption, for an initially low aphid population, of temperature-dependent exponential growth. The rate of increase was determined from spraying trials and continuous corrections improved accuracy of the short-term forecasts. Finally functional models are generally computer simulation programs which mimic the biology in detail, taking account of the age-structure of the population, the morphs and quality of its individuals, and the separate effects of all the population processes involved. While the first 2 models fulfil a tactical, predictive role, functional models have been applied in a more strategic fashion, to evaluate control methods such as the use of natural enemies (e.g., Gilbert & Hughes 1971) and to increase understanding of the pest population's behaviour. For example, a very basic functional model of bluegreen lucerne aphid (Acyrthosiphon kondoi Shinji) populations in New Zealand (Barlow in prep.) shows that alate production and dispersal, widely cited as the main probable cause of population crashes, in most cases can have only a minor effect. Outbreaks are likely to be terminated more by increased mortality, and dispersal, of nymphs and apterae. The value of predictive models is obvious but the quest for improved predictive ability through increased model sophistication has proved largely fruitless, most predictive models to date are empirical. However, the potential of computer models for increasing understanding and evaluating control options should not be under-rated. It is in this more modest, strategic role that they have proved most valuable in the past and are likely to continue to do so in the near future.
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Claims 6
Claim · model-written summary
Summer aphid numbers on cereals in the UK were negatively related to spring temperatures.
Verbatim
e0“summer aphid numbers on cereals in the UK were negatively related to spring temperatures”
Claim · model-written summary
Corrections to the green peach aphid forecast model improved the accuracy of short-term forecasts on potatoes.
- Taxon
- potatoes
Solanum tuberosume0 - Interactor
- green peach aphid (Myzus persicae Linnaeus)
Myzus persicaee0pest - Outcome
- accuracy of the short-term forecastse1
- Direction
- improvede1
- Comparator
- short-term forecastse1
- Setting
- Pennsylvaniae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“green peach aphid (Myzus persicae Linnaeus) populations on potatoes in Pennsylvania”
e1“continuous corrections improved accuracy of the short-term forecasts”
Claim · model-written summary
A functional model indicates that alate production and dispersal usually have only a minor effect on bluegreen lucerne aphid population crashes.
- Taxon
- lucerne
Medicago sativae0 - Interactor
- bluegreen lucerne aphid (Acyrthosiphon kondoi Shinji)
Acyrthosiphon kondoie0pest - Outcome
- population crashese1
- Qualifier
- in most casese1
- Setting
- New Zealande0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“bluegreen lucerne aphid (Acyrthosiphon kondoi Shinji) populations in New Zealand”
e1“alate production and dispersal, widely cited as the main probable cause of population crashes, in most cases can have only a minor effect”
Claim · model-written summary
The model suggests increased mortality and dispersal of nymphs and apterae are more likely to terminate outbreaks.
- Taxon
- lucerneMedicago sativae0
- Interactor
- bluegreen lucerne aphid (Acyrthosiphon kondoi Shinji)Acyrthosiphon kondoie0pest
- Outcome
- Outbreakse1
- Qualifier
- increased mortality, and dispersal, of nymphs and apteraee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“bluegreen lucerne aphid (Acyrthosiphon kondoi Shinji) populations in New Zealand”
e1“Outbreaks are likely to be terminated more by increased mortality, and dispersal, of nymphs and apterae”
Claim · model-written summary
Greater sophistication of predictive aphid models has yielded little improvement in predictive ability.
Verbatim
e0“the quest for improved predictive ability through increased model sophistication has proved largely fruitless”
Claim · model-written summary
Computer models are valuable for understanding aphid behavior and evaluating control options.
- Taxon
- potatoesSolanum tuberosume1
- Interactor
- green peach aphid (Myzus persicae Linnaeus)Myzus persicaee1pest
- Outcome
- increasing understanding and evaluating control optionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the potential of computer models for increasing understanding and evaluating control options should not be under-rated”
e1“green peach aphid (Myzus persicae Linnaeus) populations on potatoes in Pennsylvania”