Selection of Trichogramma for inundative biological control

This thesis presents a study of the potential for biological control of lepidopterous pests on cabbage crops in the Netherlands, by means of inundative releases of the egg parasite Trichogramma (Hymenoptera, Trichogrammatidae). The objective of this study is to investigate the usefulness of a predictive approach to the development of a biological control program. Chapter 1 provides an introduction to the three basic elements of this study: the principles of biological control, the use of Trichogramma as a control agent and the host species occurring on cabbage crops.The main theme of this study is the selection, by means of laboratory investigations and experimental field releases, of candidate strains of the parasite for practical application. This topic is discussed in chapter 2. Selection experiments were conducted using a collection of sixty geographical strains maintained in the laboratory. The methodology of culturing both parasites and hosts, and of observing female-parasite behaviour are described in chapter 3. Results of experiments on possible selection criteria involving various strains are presented in the subsequent chapters (4-9).Adaptability of parasitization activity to field-temperature conditions was investigated for all strains (chapter 4). Strains with a high performance at low temperature were used for studies on differences in host-selection behaviour between strains, i.e. host- age selection (chapter 5) and host-species selection (chapter 6). Studies on host recognition (chapter 7) and host suitability (chapter 8) were conducted to determine how and why female wasps distinguish between host species.Candidate strains selected on the basis of the laboratory research were released in Brussels sprouts fields with natural pest populations. During four seasons (1982-85) the performance of two strains in parasitism of the major host species was compared, in order to test the validity of the pre-introductory selection criteria (chapter 9). Finally, a comprehensive discussion of the results of this study is provided in chapter 10.