To what extent could resident natural enemies provide biotic resistance to future insect pest incursions?

Abstract

Economic pests pose a serious threat worldwide, with abundant literature on insect crop pests. Classical biological control – the importation of exotic natural enemies to control target pest populations – has a rich and successful history in New Zealand since the 1920’s. Despite a wealth of research into the impacts of biological control agents on their target pests, little is known about the extent to which resident natural enemies may subsequently contribute to insect pest suppression in the future, for example, of newly established pest species or biosecurity incursions (i.e. biotic resistance). Biotic resistance theory posits that communities can often resist species invasions due to natural enemies and/or competitive exclusion. We aimed to assess whether New Zealand’s parasitoid wasp fauna could provide biotic resistance to future pest incursions. A database was generated containing all intentionally and unintentionally-introduced ichneumonoids (Braconidae; Ichneumonidae) in New Zealand, which included their known global host ranges, and status of these hosts as pests, to infer potential for biotic resistance. A total of 672 host associations involve exotic pests that resident ichneumonoids could provide some level of resistance against, should they arrive. An additional 110 host associations represent pest species present in New Zealand that could currently be experiencing some level of suppression. Analysis of the database revealed that biotic resistance has accumulated over time and will likely continue to do so as more alien parasitoids are intentionally or unintentionally-introduced. It was also determined that out of 435 potential future pests, 134 could be utilised by more than one species of alien ichneumonoid already in New Zealand, amounting to multiple parasitoid resistance against certain pests. Finally, there was no significant difference in host-specificity and relative impact against targets, and thus in the potential for biotic resistance, between the agriculture, horticulture, and forestry sectors. These results have implications for pest management in New Zealand and elsewhere, in particular querying the need to import exotic natural enemies, considering the difficulties and biosecurity risks, in some pest management situations. It is recommended that biotic resistance amongst resident parasitoid fauna is researched for specific pest management scenarios and that this be used to inform decisions regarding importing exotic biological control agents.