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 st em weevil, Listronotus bonariensis. Early investigation into the biolo gy of the parasitoid indicated that there was no discrimination betwee n parasitized and unparasitized hosts. However, dissection data from t wo experiments were analyzed according to three mathematical models. M odel I was based on the Poisson distribution and assumed random select ion of hosts. The host discrimination model (model II) assumed that pa rasitized hosts had reduced attractiveness to searching parasitoids. A competition model (model III) made the assumption that competition be tween 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 m odel. Results from the laboratory experiments indicated that host disc rimination explained the results more accurately than parasitoid larva l competition. Models II and III both provided adequate fits to the fi eld data, although the departure from the observed data was greatest f or the competition model. Both intra- and inter-ecotypic host recognit ion were evident, and there was some indication that clonal recognitio n took place. This is the first evidence of host discrimination by a m ember of the genus Microctonus. It has provided further indication of the success of M. hyperodae as a biological control agent.