Do foliar phenolics provide protection to Heliothis virescens from a baculovirus?

The effects of chlorogenic acid on larval survival and growth of the tobacc o budworm Heliothis virescens and larval susceptibility to Helicoverpa tea nucleopolyhedrovirus (HzSNPV) were studied with an artificial diet and tran sgenic tobacco Nicotiana tabacum. Survival of neonates on over- or underexp ressed phenylalanine ammonia-lyase (PAL) transgenic tobacco lines was posit ively correlated with the level of chlorogenic acid. Larval weight was not correlated with the level of chlorogenic acid in tobacco foliage. On the ot her hand, larval weights on artificial diet supplemented with chlorogenic a cid were negatively correlated with chlorogenic acid concentration. Second instars treated on virus-treated (10 occlusion bodies/larva) tobacco leaf d isks for 24 hr and then reared on tobacco leaves showed higher survival tim e and increased mortality on lines with increasing levels of chlorogenic ac id. However, viral-related larval mortality on artificial diet was negative ly correlated with dietary chlorogenic acid. These results illustrate the i nadequacy of artificial diet studies in establishing causal relationships a mong plant chemistry, herbivores, and natural enemies.