Costs and benefits of plant health measures against D iabrotica : experiences and estimations for G ermany

Diabrotica virgifera virgifera has been found in G ermany since 2007, and mandatory EU plant health measures must be applied. To evaluate information on the appropriateness of these measures, we analysed benefits and costs for the two control strategies eradication and containment by ex ante data estimations and observed experiences. As a ‘no official control’ scenario, we considered that maize is grown without plant health measures where growers start to apply insecticides 5 years after D . v. virgifera damage becomes obvious. The eradication strategy consists of crop rotation with additional insecticide treatments, and the containment strategy assumes crop rotation (two times maize within 3 years) or insecticide applications against adults (two applications per year). Spread of D . v. virgifera was calculated over 15 years based on the model of Baufeld and Enzian (2005, Symposium Proceedings No. 81: Introduction and Spread of Invasive Species, 149–154), and corresponding costs for the estimated accumulated areas were analysed. Additionally, the observed spread from 2007 to 2011 in G ermany and resulting costs were compared with the estimated costs of the simulated ex ante scenarios. Eradication by crop rotation proved to be the most cost‐effective strategy for single outbreaks and a low maize density in the safety zone. In contrast, both containment strategies led to a moderate cost‐effectiveness whereof crop rotation is expected to be the more sustainable approach leading to less environmental impacts and resistance problems in the long term. Observed data showed that the range expansion of D . v. virgifera in S outhern G ermany was more rapid than expected from the low beetle numbers of the pheromone trappings leading to the assumption that both long‐distance dispersal and continuous short‐distance diffusion are involved. The observed average spread rate per year from 2007 to 2011 was estimated at 30 km. In B avaria, the containment zone comprised in 2011 about 210 000 ha of maize production leading to much higher containment costs compared to the ex ante simulations.