A population dynamics approach to the wheat bulb fly Delia coarctata problem.
A key-factor analysis is presented using data on Delia coarctata (Fall.) populations collected over 12 years from Stackyard field, Rothamsted. The analysis shows that the key-factor causing population change is variation in the number of eggs laid, and this mortality interval (kO) is also shown to be density-dependent with a time delay. Adult emigration and immigration is suggested as the major mechanism of potential egg loss, and it is speculated that the delayed aspect of its action is caused by genetic feedback acting through responses to adult density. Larval survival is shown to be dependent on both egg density 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.