A Population Dynamics Approach to the Wheat Bulb Fly Delia coarctata Problem

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Abstract
A key-factor analysis is presented using data on wheat bulb fly populations collected over 12 yr from Stackyard field, Rothamsted [England]. The key factor causing population change is variation in the number of eggs laid, and this mortality interval (ko) is density-dependent with a time delay. Adult emigration and immigration is proposed as the major mechanism of potential egg loss, and the delayed aspect of its action is thought to be caused by genetic feedback acting through responses to adult density. Larval survival is dependnet on egg and shoot density, although other factors may also be important in determining survival in different years. A population model was constructed to test the interpretations of the dynamics, and it is suggested that the further development of such a model is likely to prove more useful in improving understanding of the problem and in the development of future control procedures than previous models based on multiple regression techniques.