Abstract: Baculoviruses are potential agents for the control of different forest pests. The aim ofstudies was to extend the knowledge on insect viruses and to clarify their role in regulation ofpest populations. Nucleopolyhedroviruses (NPVs) were isolated from 15 pest species. Four NPVisolates were isolated from Hymenoptera species, 11 isolates – from Lepidoptera. Isolated viruseswere used as a basis for virus preparations. NPVs isolated in Latvia were found to be activeagainst their corresponding pests and may be successfully used as biological control agents. Thepossibilities to enhance viral infection by synergistic additives were investigated.