PARENT SESSION
Oral Session # 21: Herbivory I: Susceptability and Resistance.
Presiding: D Lincoln
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.

Induced susceptibility to leaf herbivores via floral induction.

Adler, Lynn^*,1, ¹ Virginia Tech, Blacksburg, VA

ABSTRACT- Traits that are attractive to mutualists may also be attractive to antagonists, and the evolution of phenotypic traits will depend upon the combined selection pressure due to multiple interactions. Many species of Lepidoptera are pollinators as adults and herbivores as larvae, raising the possibility that adults use floral or nectar traits to make oviposition decisions and evaluate plant quality. This may be particularly true for species that have secondary compounds in nectar if levels of nectar defenses are correlated with levels of leaf defenses. I tested the hypothesis that leaf damage by the tobacco hornworm, Manduca sexta, and fertilizer level in domestic tobacco, Nicotiana tabacum, would affect floral morphology, nectar composition, and oviposition choice by adult M. sexta moths. Damaged leaves were removed from plants prior to moth choice tests to eliminate the possibility of decisions based directly on the presence of damage. I found that fertilizer and damage both affected several floral morphological traits, including corolla length, width and diameter. Adult moths preferred to oviposit on high-fertilizer plants, and oviposited more on damaged than control plants when fertilizer levels were high but not when fertilizer was low. Thus, it appears that damage provides some indirect cue to moths making oviposition choices, but only when resources are available. Nectar composition has not yet been analyzed but I hypothesize, based on results from leaf induction, that damaged plants will have higher concentrations of nicotine in nectar and that fertilizer will enhance this effect. In future work I will experimentally manipulate nectar nicotine in field plants to determine if moths use this cue explicitly to make oviposition decisions. This research demonstrates that selection on the production of defensive compounds such as nicotine may be mediated via floral as well as leaf interactions.

Key words: nicotine, pollination, induced defenses, nectar