Argentine stem weevil behavioural responses to different parasitoids

Importation biological control can create novel host-natural enemy associations that exhibit responses different from evolved behaviours in their native range. This possibility was investigated in New Zealand based on the South American pasture pest, the Argentine stem weevil (<em>Listronotus bonariensis</em>) in the presence of three endoparasitoid species with different levels of affinity to the weevil. The first parasitoid was <em>Microctonus hyperodae</em> which has a close coevolutionary history with <em>L. bonariensis</em>. The second, was <em>M.</em> <em>aethiopoides</em> (Irish strain), which has bionomic and ecological overlaps with <em>M. hyperodae</em> and is an effective control agent of the clover root weevil <em>Sitona obsoletus </em>in pasture. The third parasitoid was <em>Aphidius colemani</em> which attacks aphids and is phylogenetically and ecologically remote from the two <em>Microctonus</em> spp. Microcosms were used to examine and compare the nature of the <em>L. bonariensis</em> responses when confronted by each of these parasitoids. Please note some behavioural, plant section by height and feeding scar raw data variables were not analysed. Here <em>M. hyperodae</em>, showed distinctive crouching and reduced feeding behaviour when confronted by <em>M. hyperodae</em>. When exposed to <em>M. aethiopoides</em>, the weevil exhibited very much reduced responses and there was no reaction whatsoever to <em>A. colmani</em>. The implications of these <em>L. bonariensis </em>behavioural responses are discussed in terms of the biogeography of the parasitoid species with reference to possible pre-adaptative behaviour.