Recent research has added much to our knowledge of the nature and significance of chemoreception in insects. This text deals with both pure and applied aspects at the ecological level, and goes on to discuss the mechanisms by which insects detect and respond to chemicals at the molecular level. Throughout the text reference is made to appropriate techniques in both field and laboratory situations in order to provide an insight into the means of investigating the subject and to indicate the areas of likely future advances. Plant-insect interactions are considered in terms of plant chemical defences and of the co-evolved insect response to these. The role of pheromones is described with an account of the factors governing their synthesis and secretion. A chapter on pheromone gland morphology is also included. The electrophysiological approach is described and also the novel use of biochemical techniques to ascertain the mode of action of plant and insect-produced chemicals. Practical applications reported include the use of natural toxins in plant protections and the exploitation of pest-resistant crop varieties.