Cuticular extracts inducing aggregation in the German cockroach, Blattella germanica (L.). 
German cockroaches Blattella germanica (L.) are gregarious insects.  An aggregation pheromone contributes to the maintenance of aggregates.  Choice experiments checked the efficiency of different solvents, i.e. dichloromethane, methanol and pentane, in extracting attractive substances and compared the attractiveness of extracts of different parts of the body.  Dichloromethane and pentane were the most efficient solvents tested for extracting the attractive substances.  Methanol whole body extracts appeared inefficient to induce aggregation.  The proportion of larvae attracted to conditioned papers decreased in relation to the size of cuticular surface washed, from whole body to half-body and again to a section of the body cut in three.  Attractive substances appear to be present on all parts of the body.  Chemical analysis by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) showed that the active extracts contained only cuticular hydrocarbons.  In addition to behavioural tests, differences between the composition of methanol extracts and that of the extracts for the other two solvents were revealed by GC.  These results indicated that the cuticular hydrocarbons operate as an aggregation pheromone in Blattella germanica.