The Interrelationships of Hypera Brunneipennis (Coleoptera: Curculionidae) and Bathyplectes Curculionis (Hymenoptera: Ichneumonidae) in Southern California1

Abstract

Hypera brunneipennis, the Egyptian alfalfa weevil, is now found in southern California in three of the four major alfalfa-producing valleys of the California desert and over much of the south coastal plain. It is attacked in these areas by a Palaearctic ichneumonid, Bathyplectes curculionis, which was originally colonized on this weevil at Yuma, Arizona, and apparently has spread with it in bales of alfalfa hay transported to market, and by natural means. The parasite destroys about one-third of the weevil population annually in the coastal areas, but is of little significance in the desert valleys. Partial immunity, effected through the lethal action of the weevil blood on the parasite's eggs, prevents parasitism by B. curculionis from reaching significantly higher proportions. The parasites originally colonized were obtained from a related alfalfa weevil, Hypera postica, and the partial immunity of H. brunneipennis indicates that the strain of B. curculionis found in southern California is not fully adapted to the latter host. Individual larvae of H. brunneipennis appear to have limited ability to inactivate eggs of this parasite, so that in superparasitized larvae one or more of the supernumerary eggs may escape encapsulation. It is anticipated that a fully adapted strain of B. curculionis will be sought from H. brunneipennis in the Near East.