Interactions between the solitary endoparasitoid Meteorus gyrator (Thunberg) and the pathogen Lacanobia oleracea (L.) granulovirus (LoGV) were investigated in the host L. oleracea. The ability of M. gyrator to develop within an LoGV-treated host was dependent on the time of parasitism relative to the time of infection. The likelihood of survival of the parasitoid increased as the time between oviposition of the parasitoid egg and ingestion of the virus by the host increased. LoGV-induced death of the host resulted in death of the developing parasitoid. No parasitoids emerged from hosts that were infected with LoGV before parasitoid oviposition. Host treatment with LoGV after parasitization had occurred had no pronounced effects on parasitoid larval or pupal developmental times or on the weight of the parasitoids’ cocoon after egression from the host. There were also no indications of direct infection or toxic effects of LoGV on the developing parasitoid larva. Adult M. gyrator were able to discriminate between healthy and LoGV-treated hosts. Hosts treated with LoGV were parasitized less frequently than untreated hosts, and fewer eggs were laid in LoGV-treated hosts. Transmission of virus from infected to healthy hosts via contamination of the wasp was low (1.5%). Percentage mortality of the host was significantly higher when a combination of the two biological control agents was used compared with either the virus or the parasitoid on its own. The practical use of these two agents was demonstrated in a glasshouse trial that confirmed that damage to tomato plants by L. oleracea larvae could be reduced using LoGV or parasitoid treatment. Although damage was further reduced by using a combination of the two agents, this was not significantly lower than that for LoGV treatment alone.