Abstract:
The lethality of malathion to all stages of red scale of three different strains was tested. Scales from areas subjected to spraying were 1.87 times as tolerant as those from unsprayed areas, which in turn were 1.52 times as tolerant as the laboratory strain. Of the seven distinguishable stages of red scale only the first moult (males and females), second moult females, and young-producing females proved to be significantly more tolerant than the other stages, the second moult female being three times as tolerant as the young-producing female, or nine times as tolerant if the body weight and surface area are taken into account. The latter finding is important, because it has been customary to estimate the efficiency of spray treatments by mortality in the young-producing stage. This would leave many of the second moult females alive after spraying and the infestation would continue.