Introduction

Biological control by introduction and permanent establishment of exotic natural enemies of pests has been practised for over 100 years. Although a few introductions of beneficial insects had been made earlier, the introduction of an Australian ladybird (Rodolia cardinalis Mulsant) into California to control the cottony cushion scale (Icerya purchasi Maskell) on citrus in 1888–9 (Caltagirone and Doutt, 1989), is generally considered to mark the beginning of the practice of biological control as an effective pest control strategy. This operation was not only highly successful in controlling the pest but also was widely publicized with the result that economic entomologists in a number of countries were soon importing ladybirds for the control of a wide range of pests in what Lounsbury (1940) referred to as the ‘ladybird fantasy’. Few of these introductions were successful, consequently practitioners began to study the ecology and population dynamics of pest natural enemy systems and a more scientific approach to biological control developed (Waage and Greathead, 1988), with a consequent increase in the success rate. However, the introduction of natural enemies remains a largely empirical activity that depends to a large extent on the knowledge and insight of the practitioner.

There are other ways in which natural enemies can be applied as pest control agents; by augmentative or inundative releases of native or exotic agents, which includes formulation of pathogens as biological pesticides (see Huber, Chapter 18; and Waage, Chapter 9) and conservation or enhancement of the action of native species of natural enemies (see Edland, Chapter 4). Because the introduction method was the first to achieve an outstanding success, it is now referred to as ‘classical biological control’.