A century of Azolla filiculoides biocontrol: the economic value of Stenopelmus rufinasus to Great Britain

Table 4 Estimated management costs for A. filiculoides under three described scenarios (in GBP £)

Scenario	Region	Mean annual cost of Stenopelmus rufinasus releases	Annual cost of traditional control—once yearly management	Annual cost of traditional control—twice yearly management	Total annual cost of control—once yearly management	Total annual cost of control – twice yearly management
Scenario 1—Azolla, no weevils	England & Wales	N/A	7,925,743	15,851,485	7,925,743	15,851,485
Scenario 1—Azolla, no weevils	Scotland	N/A	506,103	1,012,205	506,103	1,012,205
Scenario 2—Azolla, naturalised weevils	England & Wales	N/A	732,812	1,465,623	732,812	1,465,623
Scenario 2—Azolla, naturalised weevils	Scotland	N/A	47,600	95,199	47,600	95,199
Scenario 3—Azolla, naturalised and augmented weevils	England & Wales	16,109.22^a	13,443^a	26,886^a	29,552	42,995
Scenario 3—Azolla, naturalised and augmented weevils	Scotland	1038.78^a	867^a	1734^a	1906	2772

^aOf total area of A. filiculoides treated, 50% apportioned to S. rufinasus releases and 50% to traditional control methods. S. rufinasus applied only once per site per year. Value of S. rufinasus releases in England and Wales vs Scotland allocated at same proportions of total cost as traditional control costs for Scenario 3 (94% vs 6%). Mean annual value of augmentative S. rufinasus releases (2011–2020) at current prices is £17,146 ± £2633 (SE) (exclusive of VAT) (CABI unpublished)

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