Horizontal transmission of Nosema fumiferanae (Microsporidia: Nosematidae) in the spruce budworm (Choristoneura sp., Lepidoptera: Tortricidae).

摘要

Horizontal transmission dynamics of a sublethal pathogen were examined using Nosema fumiferanae and spruce budworm as a model system. Onset of spore egestion varied from 11 to 15 days post inoculation. Both onset and the number of spores egested were affected by a complex interaction between temperature and inoculation dose. When late-instar larvae were fed spores, no spores were egested. Time to adult moth eclosion was dependent on infection, sex and temperature. In the field, the proportion of infected larvae (prevalence) declined between the overwintering and the early-instar stage regardless of initial prevalence. After the third instar, prevalence and the number of spores per larva rose until pupation. Overall, I propose that successful horizontal transmission is more dependent on the length of time to encounter egested spores than spore density, and that infected larval density is critical to the increase in prevalence of N. fumiferanae in this sublethal pathogen system.