Progress in the biological control of Argentine stem weevil and comment on its potential

Abstract

Between 1988 and 1990 three visits were made to South America to search for and collect the Argentine stem weevil parasitoid Microctonus hyperodue. 'Ibis resulted in the importation of 240 parthenogenetic parasitoid lines collected from seven very different ecoclimatic zones. Each zone was assumed to have resulted in a corresponding 'ecotype'. Throughout the winter of 1991,100 000 parasitised weevils were liberated at selected sites in the northern North Island, northern South Island and Otago/Southland. During this work, care was taken to rear and release the parasitoid ecotypes in equal numbers. In this way establishment patterns of the different ecotypes in different climate zones should eventually be able to be established thereby giving new insights into the importance of parasitoid preadaptation in achieving biological control. Since its release, detailed research has been conducted into the spread and build up of Microctonus hyperodue. In most places, especially in the north, the parasitoid has established and built up to high levels of parasitism (80%) with unexpected rapidity, although its rate of spread has been modest at around l-3 km p.a. Preliminary results from both Canterbury and the northern North Island indicate that the pest potential of Argentine stem weevil population has already been substantially reduced in its release areas.