Research on the genetic regulation of insect physiology and behaviour is a fairly new field in biological research. The development of modern techniques like transcriptome studies, micro-arrays and RNA interference has altered the way we study insects. In this book, several candidate genes regulating different aspects of insect physiology and behaviour are studied in three different insect models, with a great focus on the desert locust. It was found that the genes studied in this work could, in the future, be important in solving the locust pests that threaten a large part of the worlds population. We have found that the foraging gene is implicated in the early changes during the gregarisation process of this locust and that the circadian clock genes period and timeless as well as the transcriptional factor fruitless can influence locust reproduction. These results can lead to new ways of locust pest management.