We have developed a technique for the production of live virus vaccines for arthropod vectored viruses. This technology is based on the discovery that evolution has provided these viruses with genetic information essential for replication in one of the two hosts (mammals and insects) but not the other. We have identified genetic elements required for efficient replication in the mammalian host and removed them. These deletion mutations restrict the growth of the virus to the insect host resulting in a host range mutation that is a deletion with little prospect of reversion to wild type. Injection of the insect produced virus into mammals results in the production of high titers of neutralizing antibody and protection against challenge with wild type virus in the absence of disease. In principle this technology will produce a live virus vaccine against any of these arthropod vectored diseases for which a cDNA clone can be produced. The significance of this possibility is obvious.