| Abstract: | Detailed assessment of the potential of an alien species to become a pest when introduced into a new area requires a comprehensive knowledge of the biology of that species. In the absence of such knowledge, species can be classified for temperate areas into one of four categories of risk on the basis of capacity for survival in similar climates and presence of host plants outdoors or under glass. The categories are: 1) potential outdoor pests, 2) potential glasshouse pests, 3) species that have outdoor hosts but are unlikely to become pests on them unless they adapt genetically (no hosts under glass), and 4) species that have no host plants outdoors or under glass, or are incapable of prolonged survival outdoors. Some aspects of the more detailed assessment of better known species are suitable for computer simulation modelling. The features of a phenological model currently being developed in England are briefly described. Estimates of the benefits derived from excluding a particular alien pest can be obtained from the cost of the additional annual control measures likely to be required if the pest were to be introduced. Estimates of factors such as crop losses, environmental problems and increased research and advisory work must be added to obtain a range of costs for years when pest populations are likely to be ← high →, ← normal → and ← low →. Costs of excluding the pest must include cost to government (staff costs, eradication measures, publicity etc.) and costs to industry. The resulting comparison of benefit with cost can aid decisions on the design and enforcement of phytosanitary regulations. |
