DISPLACEMENT OF BATHYPLECTES-CURCULIONIS (THOMS) (HYMENOPTERA, ICHNEUMONIDAE) BY BATHYPLECTES-ANURUS (THOMS) IN EASTERN ONTARIO POPULATIONS OF THE ALFALFA WEEVIL, HYPERA-POSTICA (GYLL) (COLEOPTERA, CURCULIONIDAE)

Bathyplectes anurus (Thoms.) has displaced B. curculionis (Thoms.) as the main larval parasitoid in populations of the alfalfa weevil, Hyper a postica (Gyll.), in eastern Ontario. Following its belated spread to the Bay of Quinte dairy belt, it used a combination of r and K strategies to assert its superiority: a greater reproductive capacity, more rapid search and handling, and more aggressive behaviour. Also, it is not subject to encapsulation by the host and reduces direct competition with the entomopathogenic fungus Zoophthora phytonomi (Arthur) by laying its eggs in older hosts that have a greater probability of escaping death from disease. Taken together, these factors have enabled it to perform better than B. curculionis and to displace it in the host—parasitoid community. Moreover, it may have the potential to stabilize weevil populations during years when the fungus is enzootic. © 1990, Entomological Society of Canada. All rights reserved.