Exotic pests and biological control in New Zealand broadacre pasture
Wednesday, 1 April 2015 – 1:00pm
Prof Stephen Goldson
Speaker: Prof Stephen Goldson, Bio-Protection Research Centre Theme leader and Senior Scientist at AgResearch.
Venue: B4, Burns Building, Lincoln University.
Although the literature shows that the loss of pest susceptibility to classical biological control agents is exceedingly rare, there are certain behavioural and ecological criteria that may well predispose to it. Such a critical combination of factors coincides with agroecosystems based on incomplete transplants imported from elsewhere, such as New Zealand pasture. It can be argued that a lack of biodiversity results in low biotic resistance to invasive species, typically resulting in spectacularly high pest densities. Exactly the same sort of thing can happen with introduced parasitoid biological control agents. Again, due to a lack of biotic resistance, very high levels of parasitism can occur, leading to a sense of triumph amongst those who organised the release programme.
However, it now seems that such euphoria may be short-lived. Very high and constant selection pressure on the pest by the control agent may result in the evolution of pest resistance. This is particularly so in ecosystems lacking host refugia. Further, this is made far worse when a parasitoid control agent reproduces parthenogenetically, whereas its host reproduces sexually. This results in an ‘unequal evolutionary arms race’ whereby the weevils have far more capacity to adapt as a result of selection pressure compared to the clonally reproducing control agent.
This talk presents evidence that much of the above is apparently occurring in the control of the Argentine stem weevil by the parasitoid Microctonus hyperodae in New Zealand pastures. If this is correct, such a pattern could also become apparent in other grassland biocontrol systems.