PARENT SESSION
Oral Session #72: Herbivory: Herbivore Response to Plants.
Presiding: C. Mitchell
Wednesday, August 7. 1:00 PM to 4:45 PM. Mesquite Room, Radisson.
Effect of mycorrhizal colonization on mirid (Tupiocoris notatus) populations feeding on tobacco (Nicotiana rustica and N. tabacum) in the greenhouse and field.
WOOLEY, STUART*,1, PAINE, TIMOTHY1, 1 University of California, Riverside, California
ABSTRACT- Mycorrhizal fungi associate with almost all land plants. It is well known that they contribute positively to plant nutrient status. However, only recently, it has been recognized that mycorrhizae may also increase a plant's ability to defend itself from insect herbivores. To date, mycorrhiza-plant-insect interactions investigators have tested hypotheses of plant-insect relations using plants producing carbon-based defenses. One hypothesis we tested was that mycorrhizal plants would have lower insect herbivore populations than non-mycorrhizal plants. We tested our hypothesis using a 2x2 (two mycorrhizal treatments x two Nicotiana species) factorial design (N=144) inoculating plants with whole soil (mycorrhizal) or autoclaved whole soil (non-mycorrhizal). Insect populations were determined weekly for 8 weeks. Mycorrhizal colonization was ~80% for the mycorrhizal treatment and up to 20% for the non-mycorrhizal treatment. We found that mirid (Tupiocoris notatus) nymphs and adults responded similarly to mycorrhizal colonization within and across species. Nymph and adult populations were significantly lower on mycorrhizal tobacco (p <.0001) for both species, when controlling for plant biomass, except nymphs on N. tabacum (p=.426). Plant biomass was also significantly affected by mycorrhizal treatment (leaf nodes p <.0001; height p=.039). Additionally, non-mycorrhizal plants were more heavily damaged than mycorrhizal plants. These results suggest that mycorrhizal colonization decreases host-plant suitability for herbivores and probably affects insect herbivore communities. Ongoing work is towards understanding these interactions in the field using native plants, herbivores and natural enemies. Finally, primary and defensive chemicals analysis will provide a clearer mechanistic understanding of these results.
KEY WORDS: multi-trophic interactions, mycorrhizae, Nicotiana, herbivory