Do plant phenolics confer resistance to specialist and generalist insect herbivores?

The impact of phenolics on a specialist herbivore, Manduca sexta, and a generalist herbivore, Heliothis virescens, was investigated using transgenic tobacco with differential expression of phenylalanine ammonia-lyase. Foliar phenolics such as chlorogenic acid, rutin, and total flavonoids differentially accumulated in the respective transgenic tobacco lines; the amount of chlorogenic acid ranged from 201 to 2202 mu g g(-1) of fresh leaf, that of total flavonoids from 211 to 500 mu g g(-1) of fresh leaf, and that of rutin from 73 to 172 mu g g(-1) of fresh leaf. However, the levels of the phenolics and larval growth of M. sexta or H.virescens were not significantly correlated. Likewise, phenolic levels were not correlated with larval survival of M. sexta. These results suggest that plant phenolics are not a determining factor for host plant:resistance against these insects in this system.