Evidence of Host Discrimination by Microctonus hyperodae Loan (Hymenoptera: Braconidae, Euphorinae), a Parasitoid of the Argentine Stem Weevil Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae)

Microctonus hyperodae is a solitary endoparasitoid of the Argentine stem weevil, Listronotus bonariensis. Early investigation into the biology of the parasitoid indicated that there was no discrimination between parasitized and unparasitized hosts. However, dissection data from two experiments were analyzed according to three mathematical models. Model I was based on the Poisson distribution and assumed random selection of hosts. The host discrimination model (model II) assumed that parasitized hosts had reduced attractiveness to searching parasitoids. A competition model (model III) made the assumption that competition between the early immature parasitoid stages led to premature mortality, which was not accounted for in the dissection results. The dissection data indicated statistically significant departure from the Poisson model. Results from the laboratory experiment indicated that host discrimination explained the results more accurately than parasitoid larval competition. Models II and III both provided adequate fits to the field data, although the departure from the observed data was greatest for the competition model. Both intra- and inter-ecotypic host recognition were evident, and there was some indication that clonal recognition took place. This is the first evidence of host discrimination by a member of the genus Microctonus. It has provided further indication of the success of M. hyperodae as a biological control agent.