The Lepidopteran densovirus-derived vector, pJlacZDeltaNS3, is a defective virus genome with an insertion of lacZ DNA in the viral structural protein coding sequence, and a deletion of the sequence coding the non-structural polypeptide NS3. pJlacZDeltaNS3 was injected into Drosophila eggs and the maintenance of the viral genome was monitored by expression of beta-galactosidase and by Southern blot hybridizations. Intense beta-galactosidase activity was observed in many somatic tissues of third-instar larvae and adult flies, in more than 60% of the injected animals. DNA analyses showed that staining in adult tissues correlated with the amplification of the vector. Together, these results suggest the occurrence of early events of integration of the vector into the Drosophila host genome.