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Population Dynamics of the Cabbage Aphid, Brevicoryne brassicae (L.)

R. D. Hughes
Journal of Animal Ecology
Vol. 32, No. 3 (Oct., 1963), pp. 393-424
DOI: 10.2307/2600
Stable URL: http://www.jstor.org/stable/2600
Page Count: 32
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Population Dynamics of the Cabbage Aphid, Brevicoryne brassicae (L.)
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Abstract

1. The population dynamics of the cabbage aphid were studied for 3 years (1960-62) at Canberra, Australia. There, the annual cycle is simplified by the virtual suppression of the sexual cycle, parthenogenetic reproduction occurring throughout the year. 2. The annual cycle can be divided into two phases: (a) autumn and winter on brassica crops, and (b) spring and summer on brassica seed-crops or cruciferous weeds. The former (a) was studied for two seasons using conventional sampling techniques. 3. An analysis of instar-distributions within the samples enables the potential rate of increase, the overall mortality rate and the reproductive rate of adults to be directly estimated for field populations. 4. With knowledge of the potential rate of increase more accurate estimates of the effect on populations of emigration and natural enemies were made possible. 5. The interaction between intrinsic and extrinsic factors affecting aphid population size could be defined in terms of (a) their effect on the potential rate of increase, and (b) the action of a change in this parameter on their own numerical effect. 6. A simple pattern of numerical change was seen to result from the action and interaction of intrinsic and extrinsic factors. This pattern could also be discerned in limited studies on the spring and summer populations on cruciferous weeds. 7. Aerial migration is clearly essential to cabbage aphid survival as its host-plants are not perennial. 8. After the initial colonization of a host-plant the aphid population increases rapidly until physiological changes occurring either independently or together within plant and aphid ensure that a large proportion of the progeny emigrate, escaping the direct consequences of overpopulation, with a finite chance of finding a new host-plant. 9. The survival of the host-plant species is ensured partly by regeneration after aphid damage and partly by the interactions between emigration, a fall in the reproductive rate, and the extrinsic mortalities, which together result in a rapid decline of aphid numbers from peak levels.

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