Stability of resistance to neguvon in the fly Musca domestica L. after cessation of laboratory selection.

Stability of resistance to neguvon was studied in three strains of Musca domestica L. after selection using different numbers of generations and different degrees of resistance. It has been found that the stability of resistance to neguvon is not always the same after cessation of selection. The loss of resistance depends on the duration of selection, i.e., on the degree of homogenization of populations with respect to resistant specimens. The degree of resistance is the function of the duration of selection to the same extent as the loss of resistance depends on it. The period of time during which the insecticide has been used is of decisive importance for the stability of resistance. The process of loss of resistance, similarly to that of its development, takes its course according to a zigzag curve, but in the opposite direction. This variation of resistance, occurring also in its development, can be explained by the heterogenity of the strains.