Table 2 Azolla filiculoides infestation rates for each water body type used in cost calculations
Scenario | Region | Azolla infestation rate (%) | Assumptions | ||||
|---|---|---|---|---|---|---|---|
Rivers and streams (%) | Canals and feeders (%) | Drainage channels (%) | Lakes and ponds (%) | Ditches (%) | |||
Scenario 1—Azolla, no weevils | England & Wales | 5.00 | 80.00 | 60.00 | 50.00 | 40.00 | Slow sections of streams and rivers at some risk, but A. filiculoides washed through system. Canals and feeders interconnected, slow moving and heavily infested. Drainage channels potentially higher flow especially in flooding periods. Medium-large sheltered lakes and ponds frequently visited by water birds heavily infested, but isolated and smaller ponds potentially A. filiculoides free. Ditches primarily associated with agriculture, poor interconnectivity across regions limiting A. filiculoides spread, less suited for water birds, but high nutrient |
Scotland | 1.00 | 16.00 | 12.00 | 10.00 | 8.00 | ||
Scenario 2—Azolla, naturalised weevils | England & Wales | 1.00 | 16.00 | 12.00 | 10.00 | 8.00 | A. filiculoides outbreaks far less frequently building up to high scale and density observed in scenario 1 before being brought under control by naturalised weevil. Spread greatly reduced, and weevil redistributed with A. filiculoides material. Scale of infestation reduced by 80% vs no weevil scenario |
Scotland | 0.20 | 3.20 | 2.40 | 2.00 | 1.60 | ||
Scenario 3—Azolla, naturalised and augmented weevils | England & Wales | 0.05 | 0.80 | 0.60 | 0.50 | 0.40 | Rate of infestation significantly lower than naturalised weevil alone, due to constant active-season shipment of weevils around the country to outbreaks. Far less A. filiculoides build up and significant infestations targeted with biocontrol. Spread greatly reduced. 99% A. filiculoides reduction vs no weevil scenario |
Scotland | 0.01 | 0.16 | 0.12 | 0.10 | 0.08 | ||