Seasonal prevalance of the cabbage aphid, Breuicoryne brassicae (LINNAEUS)

Seasonal prevalence of the cabbage aphid, Brevicoryne brassicae (L.), was studied in redish-fields of Yamaguchi University Farm from April to November in 1987. The results obtained were summarized as follows. 1) The cabbage aphid on radish was found from April to November with a lapse of no individuals in July. Two peaks were recognized on May 24 and August 10, and this seasonal prevalence was similar to those of many other species of aphids. 2) The winged viviparous females (alatae) were found from the beginning of both periods of occurrence. The ratio of the winged viviparous females increased at the end of each occurrence period. 3) The population of this species on radish in the removed fields where all arthropod species except this aphid were removed was greater than that in non-exclued fields. This result suggests that the reproduction of the cabbage aphid is affected with the presence of other Arthropoda on the same host plant. 4) The number of individuals removed from radish was 806 belonging to 9 insect orders, and 108 belonging to other Arthropoda (spiders and millipedes).