CANCELLED - Fungi round up herbivores

Background/Question/Methods Wetlands in Louisiana are rapidly degrading, mainly due to abiotic stress, which may amplify negative biotic effects.  These wetlands have been degraded, mainly, due to anthropogenic effects, and are on a trajectory toward open water.  Archips goyerana (cypress leaf roller) often attack Taxodium distichum (baldcypress) in degraded swamps in southeast Louisiana.  Defoliation by herbivores, along with flooding and increased salinity, has been shown to be deadly to these trees, further degrading Louisiana’s wetlands. Mycophyllas, fungi that live within leaves without causing any symptoms, have been shown to protect plant hosts from herbivory in some upland tree species, but this has not been shown within wetland communities. In this study I investigated the potential for mycophyllas to protect baldcypress trees from defoliation. I asked the following questions: (1) Does mycophylla diversity within baldcypress affect herbivory levels? (2) Does level of mycophylla diversity interact with stress to influence herbivory level?  We exposed baldcypress seedlings to one of three hydrologies, two salinities, and two sediment treatments. We inoculated each leaf with one of four densities of mycophyllas and applied 20 caterpillars to each seedling.  We had three true reps for a total of 36 seedlings. We measured estimated leaf area consumed per seedling.

Results/Conclusions   Preliminary results suggest caterpillars avoid leaves colonized by mycophyllas, but only when the tree is not under significant stress.  We are finding that plants exposed to fresh water, mesic or throughput hydrology, and sediment addition have the lowest level of defoliation overall.  In contrast, trees with high salinity, no sediment addition and flooded soil have the highest level of herbivory. In these high stress conditions, caterpillars do not appear to be discriminating among leaves, regardless of fungal density.  Within treatments, our results are suggesting that caterpillars prefer to eat leaves not colonized by fungi first and partially consume leaves inoculated with low densities of fungi when conditions are favorable for the seedlings.
   Our preliminary results suggest caterpillars are deterred from consuming leaves that are colonized by fungi when the plant host is healthy.  We surmise that the high leaf consumption observed in the seedlings exposed to high stress is due to lower levels of toxins produced by fungi.  This could be due to the plant host’s inability to provide nutrients to its symbiotic fungi and, therefore, the fungi do not survive or they do not invest in the production of high-energy toxins that would normally ward off herbivores.