Evaluation of a method for maintaining age-structured populations of house-flies, Musca domestica L. (Diptera: Muscidae), to study the evolution of insecticide resistance

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Abstract
An inexpensive and versatile method for maintaining age-structured Musca domestica L. populations for studies on the evolution of insecticide resistance is described. Adult flies are kept in spacious aluminium cages in which age-structuring is maintained by the thrice-weekly addition of pupae bred from eggs collected from within the cages. The population size is regulated in a density-independent manner by constraining the input of pupae to that necessary to maintain the required equilibrium density of adults within a cage. Adult numbers are monitored by photographing from outside the cage flies settled on a grid etched on the rear wall, and by converting this grid count to an estimate of population size using a calculated regression line. Observed changes in fly numbers in a cage accorded well with those predicted by a computer model using empirical data on larval productivity, and the emergence and survivorship schedules of adult flies. Since a variety of insecticide control regimes can be applied within the cage, this system enables an adequate yet tractable simulation of selection for resistance by insecticides under field conditions.