Understanding Spread Probability in Pest Risk Analysis

1. Pest Risk Analysis (PRA) Stage 2: Pest Risk Assessment Probability of Spread Pest Risk Analysis (PRA) Training

2. Stages • Stage 1: Initiation • Stage 2: Pest Risk Assessment • Step 1: Pest Categorization • Step 2: Assessment of the Probability of Introduction (entry, establishment) and Spread • Step 3: Impacts • Step 4: Overall Assessment of Risk • Step 5: Uncertainty • Stage 3: Pest Risk Management

3. CFIA-ACIA Probability of Spread • Means of spread • How? • Rate of spread • How fast? • Magnitude of spread • How far?

4. Rate and Magnitude of Spread • Probability of spread influences • Scale of potential impacts • Urgency of potential responses • Survey design • Potential success of any future control or eradication program

5. Factors influencing spread • Suitability of environment • Biology of the pest • Presence of natural barriers • Intended end use of the commodity • Production / harvesting practices • Vectors • Natural enemies • History elsewhere

6. CFIA-ACIA Factors influencing spread • Suitability of environment • Biology of the pest • Presence of natural barriers • Intended end use of the commodity • Vectors • Natural enemies • History elsewhere

7. CFIA-ACIA Factors influencing spread • Suitability of environment √ • Biology of the pest • Presence of natural barriers • Intended end use of the commodity • Vectors • Natural enemies • History elsewhere

8. CFIA-ACIA Factors influencing spread • Suitability of environment √ • Biology of the pest √ • Presence of natural barriers • Intended end use of the commodity • Vectors • Natural enemies • History elsewhere

9. CFIA-ACIA Factors influencing spread • Suitability of environment √ • Biology of the pest √ • Presence of natural barriers √ • Intended end use of the commodity • Vectors • Natural enemies • History elsewhere

10. CFIA-ACIA Factors influencing spread • Suitability of environment √ • Biology of the pest √ • Presence of natural barriers √ • Intended end use of the commodity • Vectors • Natural enemies • History elsewhere

11. CFIA-ACIA Factors influencing spread • Suitability of environment √ • Biology of the pest √ • Presence of natural barriers √ • Intended end use of the commodity √ • Vectors • Natural enemies √ • History elsewhere

12. Using the Gypsy Moth experience to predict behaviour of other species • Predicting spread of related or similar organisms • Species X is expected to behave much as did Gypsy moth, e.g., another Lymantria species such as nun moth • Comparison with dissimilar organisms • Species Y will spread faster & further than Gypsy moth, e.g., a rust of field crops • Species Z will spread more slowly & less far than Gypsy moth, e.g., a root-feeding nematode

13. Looking back is easy • Understand why spread occurred as it did • Pest risk assessment looks forward • Much more challenging

14. How to assess spread • Comparative analysis • qualitative • Predictive Models • semi-quantitative or quantitative • Useful information sources • Case histories of comparable pests • Assessments and information from areas where the pest is present • Life history information • Site information • Expert opinion

15. Spread Models • Model Types • Spatial or temporal models • Quantitative or qualitative models • Selecting a model • Fit for purpose • Scale & time are important • Challenges • Subjectivity in selection of parameters • Lack of or contradictory data • Difficult to validate

16. CFIA-ACIA Case Study: Plum Pox Virus • Background • Aphid-transmitted potyvirus • Hosts include peaches, plums, apricots • PRA Area • All of Canada • Intensive fruit production areas in distinct regions in western, central and eastern Canada • Pathways • Nursery stock, budwood - certain • Infested fruit – uncertain • Aphids

17. Factors Influencing Spread Potential • Natural factors favouring spread: • Many small orchards in close proximity to each other • Urban development adjacent (ornamental host trees) • Natural areas along north ridge with many hosts species • Several suitable aphid vectors present • Aphids fly short distances, skipping trees to feed • Natural factors against spread: • Fruit-growing regions geographically distant • Western growing region very dry; aphids low or absent • Central growing region extremely hot summers; aphids low or absent

18. Factors Influencing Spread Potential • Human factors favouring spread: • Trees propagated vegetatively • Individual growers hold lands distributed throughout region • Fruit trees and nursery trees destined for domestic use are not virus-tested • Symptoms are cryptic; growers are not generally aware • Aphid control not generally considered necessary • Mixture of fruit tree & ornamental hosts produced commercially in central region • Human factors against spread: • Most propagation conducted locally • Little or no movement of plant material between regions

19. CFIA-ACIA Extrapolating from other situations to predict spread • What is the history of spread of PPV in Europe? • How does the situation in North America differ from that of Europe? • How will these differences influence PPV spread? • Use of hard data, observation & expert opinion

20. CFIA-ACIA Spread Potential • Life history • Area of origin factors • PRA Area factors • Human factors • Compare to other pests • Compare to other places • Means of spread • How? • Rate of spread • How fast? • Magnitude of spread • How far?

21. Stages • Stage 1: Initiation • Stage 2: Pest Risk Assessment • Step 1: Pest Categorization • Step 2: Assessment of the Probability of Introduction (entry, establishment) and Spread • Step 3: Impacts • Step 4: Overall Assessment of Risk • Step 5: Uncertainty • Stage 3: Pest Risk Management