Automatic Time/Response Records with Drosophila

Abstract

Drosophila melanogaster Meig. is widely used for bioassay of insecticides. In developing a method for bioassay of insecticide residues in soil, we have found it necessary to use a time/response technique similar in principle to that employed by Callaway, Dirnhuber and Wilson¹. In comparison with the more usual dose/response techniques, the sensitivity² and also the useful range of the assay can be increased by this means. However, with a time/response technique, two main difficulties arise when attempts are made to obtain records at precise times in order to follow accurately a given programme of observations. The response of each group of flies takes a finite time to assess and so, when many groups are involved, discrepancies occur between the desired and the actual times of the counts. Unless allowances are made for these time discrepancies—a tedious process—errors are introduced which can be important when the intervals between the records are small. Furthermore, it is often necessary to record responses throughout a 24-hr. period, or even longer, and this creates an obvious practical problem which, in the past, must have discouraged the use of time/response techniques as routine methods.