Optimizing Risk Management Strategies for the Control of Philornis downsi—A Threat to Birds in the Galápagos Islands

Abstract

One of the most concerning threats to Galápagos bird populations, including some critically endangered species, is the invasive parasitic fly Philornis downsi. While long-term sustained solutions are under study, immediate actions are needed to reduce the impacts of this fly. Application of permethrin to birds's nests has been successfully done, but there might be potential long-term reproductive effects to birds. Cyromazine, an insect growth regulator, has been proposed as an alternative, but its risks and effectiveness are unknown. The goal of this study was to assist managers to determine which combination of chemical (permethrin or cyromazine) and mode of application (injection, spray, and self-fumigation) was likely to be most effective to control P. downsi while minimizing toxicity to small land birds in Galápagos, given data available and high levels of uncertainty in some cases. This study is presented as a semi-quantitative risk assessment employing the use of a multi-criteria decision analysis (MCDA) model. For the six potential alternatives resulting from the combination of chemical and mode of application, the criteria were given a score from 1 to 6 supported by available evidence from the literature and from expert opinion. In addition, three different scenarios with different sets of weights for each criterion were assessed with stakeholder's input. Considering the scenario with higher weight to effectiveness of the method against P. downsi while also weighing heavily to minimize the toxicity to birds, cyromazine spray followed by permethrin injection were the preferred strategies. Self-fumigation was the mode of application with highest uncertainty but with much potential to be further explored for its feasibility. The approach taken here to evaluate mitigation strategies against an important threat for avian species in Galápagos can also be used in other conservation programs when making real time decisions under uncertainty.