KEY-FACTOR ANALYSIS OF POPULATION FLUCTUATIONS IN ANDRACA-BIPUNCTATA WALKER (LEPIDOPTERA, BOMBYCIDAE)

The causes of fluctuation and stabilisation in a population of Andraca bipunctata Wlk. on tea in India were assessed over three years using the technique of key-factor analysis. Failure to produce the maximum complement of eggs, together with female mortality and adult migration, is shown to be the key-factor. Other mortality factors include non-viability of eggs and parasitism of the caterpillars by the tachinid Cylindromyia sp. Mortality of the female pupae tends to stabilise the population by compensating for losses due to the key-factor, but neither this nor any other mortality factors appear to be significantly density-dependent. The need for devising specialised sampling procedures and statistical tests for tropical insect populations is discussed. © 1979, Cambridge University Press. All rights reserved.