Numbers of mdg1, mdg3, gypsy and copia have been studied in several strains of D.melanogaster and D.simulans. Mean number of mdg1 and copia sites are drastically reduced in D.simulans. Majority of mdg1 and copia sites, and one third of mdg3 sites, are in hot spots for insertion, particularly in D.simulans. Southern blot analysis indicates that the majority of mdg1 and copia are in the euchromatin of D.melanogaster but the heterochromatin of D.simulans.