38th Annual Meeting of the Society for Invertebrate Pathology

Vertical transmission is common for pathogens of relatively low virulence because successful larval development, adult emergence, mating and reproduction of the infected host must occur after an infection is acquired, usually during the larval stages. Most microsporidia that are vertically transmitted are also horizontally transmitted, whether in a single host species or via an intermediate or alternate host. This would appear to favor the persistence of microsporidia released as classical biological control agents against their natural hosts. From a different perspective, successful transovarial transmission requires an explicit interaction between a pathogen and its host, and probably limits the ability of microsporidia to host switch. Laboratory studies of European corn borer, Ostrinia nubilalis larvae challenged by Nosema spp. and Vairimorpha spp. isolated from other stem-boring and row crop hosts showed that transmission, both horizontal and vertical, is a barrier to successful invasion of nontarget species. Vertical transmission is probably more stringent than horizontal transmission. Transmission experiments, therefore, may provide a more refined laboratory test of host specificity for microsporidia that are orally infective to nontarget hosts.