Life Table and Key Factor Studies of Ctenarytaina thysanura Ferris and Klyver (Hemiptera: Psyllidae) on Boronia megastigma Nees. ex Bartl. (Rutaceae) in Tasmania

Abstract

The psyllid pest Ctenary/aina thysanura was studied intensively in Tasmania, Australia for nine generations from 1986 to 1989, and the identification and quantification of different mortality factors determined by key factor analysis. The analysis identified mortalities of late stage nymphs as key factors influencing C. thysanura populations. Simple graphical analysis suggested that the more predators and parasitoids there are per prey individual the higher the relative prey mortality and that predators and parasitoids acted as regulating agents at low psyllid densities but once the psyllid attained higher densities the negative feedback regulating effect is disengaged. The predators and parasitoids acted in a delayed density dependent manner with a negative feedback delay of two generations. In the absence of these agencies, through indiscriminate spraying, psyllid numbers increased significantly to be ultimately limited by an absence of the essential resource, the terminal shoot. Intraspecific competition for space and food during host plant deterioration resulted in reduction of size and emigration of adult psyllids.