Different parasitoid species elicit varied Argentine stem weevil, Listronotus bonariensis, avoidance responses

Importation biological control can create new host-natural enemy responses that are different from those behaviours elicited in native ranges of the agent, and/or the pest. This possibility was investigated with the Argentine stem weevil (Listronotus bonariensis) in the presence of three endoparasitoid species with different levels of affinity to the weevil in New Zealand pasture. The question posed was whether the weevil exhibits species-specific or generic responses to the three parasitoids. The first parasitoid was Microctonus hyperodae which has a coevolutionary history with L. bonariensis. The second, was Microctonus aethiopoides, which has similar ecological and behavioural characteristics to M. hyperodae. The third parasitoid was Aphidius colemani, which attacks pasture aphids and is phylogenetically remote from the Microctonus spp. Microcosms were used to examine and compare the L. bonariensis responses when confronted by each of these parasitoids. L. bonariensis showed strong behavioural responses when confronted by M. hyperodae and similar, but very much reduced responses when exposed to M. aethiopoides. The weevil exhibited no measured reaction to A. colmani. Therefore, L. bonariensis showed a species-specific response to M. hyperodae rather than a generic response. The implications of the L. bonariensis behavioural responses to all three parasitoids are discussed in terms of the species’ phenotypic closeness and centres of origin.