The fruit fly Drosophila melanogaster is a model organism in genetics that has contributed significantly to our current understanding of neurology and behavioural biology. Upon optogenetic stimulation of freely moving lilli189Y-Gal4 > UAS-CsChrimson larvae, we observed increased aggregation of larvae compared to wildtype controls. Interestingly, larvae furthermore showed excessive feeding, even if toxic concentrations of additives were present. This culminated in aggressive behaviour where larvae started to devour conspecifics in the absence of other organic media. Stereotyped behavioural or physiological responses such as attraction or avoidance in subjects of the same species are often induced by chemosensory cues such as pheromones, which are typically secreted by specialized glands or tissues. Here, we investigate developing Drosophila larvae, with a focus on behavior-determining pheromone compositions of female and male larvae from wildtype and transgenes showing altered behaviour. While former analysis of pheromone excretion in Drosophila melanogaster was mainly performed for adult flies, this work presents a method to examine secreted pheromones in the larval stage using gas chromatography and mass spectroscopy (GC/MS). In order to understand which cells contribute to which behaviour, optogenetics, a method where light-sensitive ion channels are introduced into cells via genetic insertion, is used. This procedure can enable precise control of neurons using light. In the course of this project, lilli189Y-Gal4 > UAS-CsChrimson and lilli189Y-Gal4 > UAS-GtACR2 were optogenetically stimulated and detected pheromones and their composition were compared to the wildtype.