Abundance, phenology and impact of biocontrol agents on nodding thistle (Carduus nutans) in Canterbury 35 years into a biocontrol programme

摘要

Abstract Classical weed biocontrol has long been criticised, worldwide, for a lack of post-release long-term monitoring. This paper reports on a rare opportunity to follow up, three agents and 35 years later, a biocontrol programme against nodding thistle (Carduus nutans) in New Zealand. In New Zealand, the establishment of all three agents has been reported previously, but impacts have only been assessed for the receptacle weevil (Rhinocyllus conicus). This paper reports on the abundance of the nodding thistle crown weevil (Trichosirocalus horridus), and on the abundance, phenology and impact of the seed predators, R. conicus and Urophora solstitialis, in Canterbury, based on field surveys and, for the seed predators, also from a cultivated population. Trichosirocalus horridus was abundant at all field sites and on rosettes of all sizes. Seed destruction per larva by R. conicus (34 seeds per larva) was similar to previous estimates, but U. solstitialis achieved rates (21 seeds per larva) three times high...