Together again: the invasive mustard Hesperis matronalis suffers devastating seed predation by a recently adventive specialist weevil

Abstract

The enemy release hypothesis underpins classical (or importation) biocontrol as a management technique for invasive species. Classical biocontrol has had resounding success when prospective control agents have been subject to appropriate screening before release. Occasionally, however, natural enemies have been reunited with their hosts accidentally. Such adventive agents may provide effective control but have also avoided the careful screening characteristic of modern importation biocontrol programmes. We were studying the invasive mustard, Hesperis matronalis L. (Dame’s rocket; Brassicaceae: Hesperidae), when we discovered rampant seed predation by an unknown seed predator. Using DNA barcoding, we identified this seed predator as Ceutorhynchus inaffectatus Gyllenhal (Coleoptera: Curculionidae), a recently (2018) detected species in North America. Comparing potential and realised seed production, we found that seed predation by C. inaffectatus strongly reduces H. matronalis fecundity, and that this effect was not moderated by infection with turnip mosaic virus (TuMV), a commercially important pathogen hosted by H. matronalis and transmitted by polyphagous aphid species. C. inaffectatus is expected to be highly host-specific, and the absence of native Hesperidae species in North America suggests the potential for C. inaffectatus as a classical, but adventive, biocontrol agent of H. matronalis . We suggest population genetic research to identify the origin of C. inaffectatus , and host specificity testing before any intentional redistribution of this species for H. matronalis biocontrol. More generally, this system acts as a model for biocontrol prospects with adventive insect herbivore species.

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