Alternative Routes for the Horizontal Transmission of a Nucleopolyhedrovirus

Two alternative routes for nucleopolyhedrovirus transmission were investigated using Mamestra brassicae larvae: cannibalism of infected larvae and the release of virus prior to the death of the diseased host. The low frequency of cannibalism observed suggests that this is not a relevant transmission route in this species. However, larvae were shown to transfer viable virus to the environment before death through either defecation or regurgitation. Over 40% mortality was observed in larvae reared in diet containers where infected hosts had previously fed. Virus transfer to cabbages also occurred before death of the infected host, as revealed by plant bioassay. Virus was not detected in the feces or regurgitate of diseased larvae until the late stages of infection.