Evidence does not support the targeting of cryptic invaders at the subspecies level using classical biological control: the example of Phragmites

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Classical biocontrol constitutes the importation of natural enemies from a native range to control a non-native pest. This is challenging when the target organism is phylogenetically close to a sympatric non-target form. Recent papers have proposed and recommended that two European moths (Archanara spp.) be introduced to North America to control non-native Phragmites australis australis, claiming they would not adversely affect native P. australis americanus. We assert that these papers overlooked research contradicting their conclusions and that the authors recommended release of the non-native moths despite results of their own studies indicating that attack on native Phragmites is possible after field release. Furthermore, their open-field, host-specificity tests were conducted in non-wetland fields in Switzerland using potted plants, reflecting considerably different conditions than those of North American wetlands. Also, native Phragmites in eastern North America has declined, increasing its potential vulnerability to any new stressors. Because all inadvertently introduced, established, Phragmites-specialist, herbivorous insects have done more harm to native than non-native Phragmites, native Phragmites may experience more intense herbivory than non-native Phragmites from the introduction of Archanara spp. due to demographic mechanisms (e.g., increase in density of the biocontrol agent and spillover onto alternate hosts) or because the herbivores may undergo genetic change. In addition to the risk to native Phragmites, significant biomass reduction of non-native Phragmites may decrease important ecosystem services, including soil accretion in wetlands affected by sea level rise. We strongly caution against the approval of Archanara spp. as biocontrol agents for non-native Phragmites in North America.

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Biological Invasions