Studies of the ecology of the cabbage aphid (Brevicoryne brassicae (L.)) on brassica field crops in Canterbury, New Zealand: II. Population study, 1959-60

Results are presented from a second year of replicated trials dealing wilh field population studies of the cabbage aphid (Brevicoryne hrassicae (L.)) on five varieties of brassica crops at three sites in Canterbury, New Zealand. Total aphids and total alates on plants were counted throughout the year at weekly or fortnightly intervals, and plants and leaves were weighed. Alate aphids were trapped at crop height. Plant survival against combined aphid-virus attack was tested in counts taken at the peak of growth. Three resistant varieties were colonised by aphids at a lower rate than two susceptible varieties, and these differences were consistent at all sites. Plant survival at the end of six months differed significantly between sites. During the vegetative stage, aphid numbers per site were approximately proportional to leaf weight, but this relationship was not maintained during the flowering and seeding stage. Once aphids entered the crop, alate production on plants and alate numbers on traps showed some relationship, with marked autumn and spring peaks. Analyses between varieties within sites are presented, together with some analyses between sites and varie~ies. Over-all means are tabulated, but detailed analysis of these will be given in a later publication when comparisons between years will also be possible.