The over wintering of the cabbage aphid (Brevicoryne brassicae) on farm crops in the South Island of New Zealand

Abstract

Abstract As part of a long-term study of the cabbage aphid as it affects farm crops in the South Island, a survey was made of the farm crops of brassicas still standing in July and August 1958, covering Ashburton County, and in July and August 1959, covering the Rakaia-Waimakariri area. A total of 237 paddocks was sampled, and the data subjected to analysis of variance. Populations on turnips were significantly lower at the 1 per cent level than on other crops, which showed no significant differences. Weeds played little part in over-wintering of the pest, and rape seed crops were shown to receive their initial infestation from small numbers of alates flying in winter. Utilisation of crops during winter leaves chou moellier, rape, and weeds as the sources of spring infestation. The implications of these facts for control are briefly discussed.