Contemporary approaches to the study of host-parasite interactions: an introduction.

Elucidating the biochemical basis of host-parasite relationships will be instrumental in the success of biologically based control in agriculture. This challenge is an ambitious one, but several central themes emerge regarding the roles of both parasiteand host-derived molecules. These include their contribution to nematode attraction, recognition, and reproduction as well as the response of plant hosts. Identification of the gene products involving such fundamental biological processes as nematode behavior and sex determination, although not usually considered as direct participants at the host-parasite interface, will also expand our knowledge of host-parasite interactions and provide alternative strategies for pest management. The complex nature of plant-nematode interactions and the obligate parasitism of many phytopathogenic nematodes have combined to hinder progress on elucidating mechanisms involved in events such as feeding site initiation and plant responses. With the adoption of molecular biology techniques to plant nematology, new lines of research have been opened in these areas. Rapid advances in understanding the basic biology of the free-living nematode Caenorhabditis elegans will most certainly ease the tasks that lie ahead. Answers to such seminal questions as "What makes