Economic outcome of classical biological control: a case study on the Eucalyptus snout beetle, Gonipterus platensis, and the Parasitoid Anaphes nitens

Despite the importance of invasive pests, few studies address the costs and benefits of the strategies used to control them. The present work assesses the economic impact of the Eucalyptus snout beetle, Gonipterus platensis, and the benefits resulting from its biological control with Anaphes nitens in Portugal, over a 20-year period. Comparisons were made between the real situation (with A. nitens) and three scenarios without biological control: 1) replacement of Eucalyptus globulus by resistant eucalypts; 2) insecticide use; and 3) offset of yield losses by imported wood. A cost-benefit analysis was performed to evaluate a programme that aimed to accelerate A. nitens establishment. Although A. nitens provides adequate pest control in several regions, 46% of the area planted with eucalypts is affected by the beetle, causing wood losses of 648 M euros over 20 years. Losses in the three hypothetical scenarios were estimated at 2451 M-7164 M euros, resulting in benefits from biological control of 1803 M–6516 M euros, despite the fact that only partial success was achieved. Anticipating biological control by just one, two, or three years resulted in benefit-cost ratios of 67, 190, and 347, respectively. Because nonmarket values were not accounted for, these figures are likely underestimated.