Folivory and disease occurrence on Ludwigia hexapetala in Guntersville Reservoir

Authors: HARMS, NATHAN - Us Army Corp Of Engineers (USACE); SHEARER, JUDY - Us Army Corp Of Engineers (USACE); Grodowitz, Michael

Submitted to: Journal of Aquatic Plant Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary: Leaf feeding, disease occurrence and herbivore/fungal pathogen communities on the introduced wetland species Ludwigia hexapetala at Guntersville Reservoir, AL. Plant populations were examined on three dates from May to September, 2014. A complex of indigenous herbivore and fungal taxa, mostly known from other Ludwigia spp., were identified and leaf damage and disease occurrence enumerated. Fourteen insect leaf feeders and seven fungal pathogens were identified. Generally, insect feeding decreased over the growing season with a corresponding increase in disease occurence. Despite clear impacts and presence of damaging insect herbivores L. hexapetala continues to persist as a nuisance species at this site. These results, along with past surveys and literature review, also demonstrate the ability of common Ludwigia arthropod herbivores in the U.S. to host-switch between different species of Ludwigia. This raises the question as to whether potential biocontrol agents of L. hexapetala collected outside the U.S. will be sufficiently host-specific with little to no risk to native Ludwigia spp.

Technical Abstract: We report leaf feeding, disease occurrence and associated indigenous herbivore/fungal pathogen communities on the introduced wetland species Ludwigia hexapetala at Guntersville Reservoir, AL. Plant populations were sampled on three dates from May to September, 2014. A complex of indigenous herbivore and funga, taxa mostly known from other Ludwigia spp., resulted in peak feeding and disease occurrence of 88% and 92% of sampled leaves, respectively. Herbivore damage declined over the growing season from 78 to 21% of sampled leaves while disease symptom occurrence increased from 0 to 80%. Total leaf damage from both herbivory and disease was determined by software image analyses of floating and aerial leaves and reached a maximum of 14% total reduction in photosynthetic tissues by September 2014. Aerial leaves were more commonly affected by disease symptoms while floating leaves had a greater incidence of herbivore damage. Fourteen insect herbivore and 7 fungal taxa were associated with L. hexapetala at Guntersville Reservoir. Despite clear impacts and presence of damaging taxa, L. hexapetala continues to persist as a nuisance species at this and other sites in southeastern U.S. These results, along with past surveys and literature review, also demonstrate the ability of common Ludwigia arthropod herbivores in the US to host-switch between Ludwigia spp., raising the question as to whether potential biocontrol agents of L. hexapetala collected outside the U.S. will be sufficiently host-specific to present little to no risk to native Ludwigia spp.