The insecticidal potential of Galleria mellonella densovirus (GmDNV) in third, fourth, and fifth instar larvae of the host, the greater wax moth, as a step toward the construction of a molecular vector for the introduction and expression of foreign genes in the larvae of these insects was studied. Third instar larvae are most susceptible to GmDNV. Viral RNA synthesis is more rapid in this stage and slowest in the fifth instar. Infection of prepupae by intradermic injection or by horizontal spread inhibited pupation. GmDNV DNA is also infectious when introduced as a calcium phosphate precipitate. The two putative viral promoters were shown to be capable of driving the expression of the reporter gene chloramphenicol acetyltransferase (CAT) in DNA-injected larvae.