Print PageBiological control focuses on the use of natural enemies to reduce the local abundance or density of the pest. However, this paradigm makes no mention of the control of spatial invasion, mediated by enemy effects on pest dispersal and spread rates. We used a combination of empirical data on seed production, seed release, and seed terminal velocity and population spread rate modeling to quantify the effects of herbivory by the biocontrol agent weevil, Rhinocyllus conicus, on seed dispersal and population spread rates of the invasive thistle, Carduus nutans.
Results/Conclusions
We show that, in addition to reducing C. nutans seed production, R. conicus also inhibits both the release and dispersal of seeds by wind. We further show that this combination of effects gives rise to different relative impacts on spatial and local control in populations in the USA and New Zealand. Screenings of potential biocontrol agents should examine the effects of agents on host dispersal and spread, as well as on host abundance, and practitioners should also refine their objectives to specify whether control of pest population abundance or spread rates is most desired.
