Biological control: the use of living organisms (natural enemies) to control other living organisms (pests) is usually unsuccessful (Hokkanen 1985). Biological control of pink wax scale, Ceroplastes rubens
Maskell (Hemiptera: Coccidae), on citrus in south-east Queensland however, provides a good example of a "success" (Smith 1986). In most citrus growing areas, it is claimed that densities of pink wax scale were reduced from economically damaging levels to nearly zero adults per leaf within several years of the introduction of the parasitoid Anicetus beneficus
Ishii and Yasumatsu (Hymenoptera: Encyrtidae) (Smith 1986). In contrast, biological control of C rubens
on umbrella trees, Schefflera actinophylla
(Endl.), has not been as successful.
Outbreaks of pink wax scale still occur and in some cases these have persisted for a decade or more (D. Smith pers. comm.; M.P. Zalucki pers. comm.).
The problem of outbreaks of pink wax scale on umbrella trees is the topic of my Honours project. The aims of my project are to document the occurrence of outbreaks and biological control of pink wax scale in south-east Queensland and experimentally test possible hypotheses for the causation of outbreaks. Project findings are presented in
a series of four scientific papers (see chapters 3-6).
Chapter 2 comprises a review of biological control theory, especially in relation to empirical evidence from scale insect biological control programs including pink wax scale. Chapter 3 discusses the spatial distribution of pink wax scale in south-east Queensland and outlines factors that may influence the distribution and abundance of pink wax scale. Variation in size, fecundity, survival and mortality of C. rubens within and among umbrella trees is presented in chapter 4. Biological control of C. rubens on
umbrella trees is presented in two papers: identification and evaluation of natural enemies (chapter 5) and the level and distribution of parasitism (chapter 6). Chapter 7 presents the major conclusions from the study and suggests research directions for future studies.