The bionomics ofListronotus bonariensis(Coleoptera: Curculionidae) in Canterbury, New Zealand

Abstract

AbstractA study was conducted in 1990–1995 in Canterbury, New Zealand to describe the phenology and seasonal abundance of all stages of the Argentine stem weevilListronotus bonariensis(Kuschel), a New Zealand pest of Gramineae. Of note were major fluctuations in the densities of all stages from one season to the next which were not explained directly in terms of the availability ofNeotyphodium lolii-free ryegrass tillers. The overwintering mortality rates ofL. bonariensiswere found to be linear and remarkably similar between seasons and locations in the absence of pathogens. This study also showed that care must be taken in the use of existing data to analyse the impact of the recently introduced South American parasitoid waspMicroctonus hyperodaeLoan as a biological control agent ofL. bonariensis; errors may exist because of earlier sampling biases. In spite of the confounding effects of seasonal variation in theL. bonariensispopulation, reduction in the size of theL. bonariensisfirst summer generation egg and larval peaks coincided with a build up ofM. hyperodae.