The impact of plant identity and induced effects on within- and trans-generational disease resistance in the cabbage looper Trichoplusia ni

Secondary plant metabolites can have a significant impact on the susceptibility of Lepidoptera to baculovirus infection, both directly and indirectly, and thus can play a major role in determining insect fitness. Here I first examine the effects of diet complexity on the resistance of the cabbage looper (Trichoplusia ni) to a nucleopolyhedrovirus (TnSNPV). I then tested whether induction of plant secondary chemicals as a result of insect feeding impacts transgenerational disease resistance. I found that larvae fed on a mixed plant diet had similar resistance to virus as larvae fed on single species diets. However, larvae fed on tomato prior to virus challenge had higher resistance to virus, compared to those fed on cabbage and broccoli. Plant induction did not affect transgenerational virus resistance, although offspring mortality was lower for insects whose parents fed on broccoli compared to cabbage. This suggests that plant defensive chemistry has longer-term, indirect effects on disease resistance which could impact host dynamics.