Articles
MODELLING PLANT-PEST-PREDATOR INTERACTIONS WITH THRESHOLD CONTROL
Article number
803_6
Pages
61 – 68
Language
English
Abstract
Control measures used against orchard pests affect more than just the pest population.
Populations of predators are also affected, both directly and indirectly, so the balance of the ecosystem is altered in ways that may have long-term effects that are not immediately obvious.
We describe here a simple model of Plant-Pest-Predator interactions, based on a biomass flow from plant to pest to predator.
The interactions between the plant, pest and predator are specified in ratio-dependent form, and predators are permitted some degree of mobility, with rates of immigration or emigration dependent on current predator and pest numbers.
Some of the character of the complex dynamics of such a model is captured by considering the steady states of the system and their stability and the dependence of these characteristics on the parameter values describing growth rates and interactions.
Two possible steady states are of particular interest: the desirable steady state with no pests, and the steady state in which plant, pest and predator co-exist.
Integrated Pest Management (IPM) protocols often specify that pesticides should be used only when the pest density reaches a certain threshold, rather than being applied on fixed calendar dates independent of need.
An analysis of some examples of such threshold control demonstrates a wide range of possible behaviours.
In some cases, depending on parameter values and the specificity of the control measure, it is possible for threshold control to prevent a system from reaching the desirable steady state with no pests.
Populations of predators are also affected, both directly and indirectly, so the balance of the ecosystem is altered in ways that may have long-term effects that are not immediately obvious.
We describe here a simple model of Plant-Pest-Predator interactions, based on a biomass flow from plant to pest to predator.
The interactions between the plant, pest and predator are specified in ratio-dependent form, and predators are permitted some degree of mobility, with rates of immigration or emigration dependent on current predator and pest numbers.
Some of the character of the complex dynamics of such a model is captured by considering the steady states of the system and their stability and the dependence of these characteristics on the parameter values describing growth rates and interactions.
Two possible steady states are of particular interest: the desirable steady state with no pests, and the steady state in which plant, pest and predator co-exist.
Integrated Pest Management (IPM) protocols often specify that pesticides should be used only when the pest density reaches a certain threshold, rather than being applied on fixed calendar dates independent of need.
An analysis of some examples of such threshold control demonstrates a wide range of possible behaviours.
In some cases, depending on parameter values and the specificity of the control measure, it is possible for threshold control to prevent a system from reaching the desirable steady state with no pests.
Authors
A. Hall, F. Lescourret
Keywords
tritrophic model, steady state, pest control, green peach aphid, IPM
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