Population dynamics of the cabbage aphid Brevicoryne Brassicae (L.) (Homoptera:Aphididae in Vancouver, British Columbia : a quantitative study an synthesis of ecological relationships

The population dynamics of the cabbage aphid (Brevicoryne brassicae) were studied on Maris Kestrel kale during the summer months, in Vancouver British Columbia, Canada. The object was to describe the temporal variation in numbers, age distribution, and quality of B. brassicae in terms of quantitative relationships between the aphid and its biotic and abiotic environment, using a simulation model. A technique was developed whereby aphid fecundity and developmental time could be estimated for aphids within the population. Aphid fecundity and rate of development decreased continuously through the season, probably in response to changes in plant quality. The plant rarely posed an upper limit on aphid increase, but populations consistently showed an initial maximal rate of increase followed by a leveling off, and eventual population decline in the autumn. Evidence presented, suggests that syrphid predation was largely responsible for the major mid-season shifts in the rate of increase of the aphid. Thompson's (1924) 'random search' model did not adequately represent syrphid predation, and further detailed studies are required. Decreasing aphid developmental and reproductive rates, production of oviparae, predation, and leaf fall, were probably responsible for population declines in the autumn. The cabbage aphid system is compared with that described by Hughes (l963) and Hughes & Gilbert (1968). The problems of generality and biological control are discussed.Land and Food Systems, Faculty ofGraduat