Austromusotima camptozonale (Lepidoptera: Crambidae) Herbivory Results in Frond and Rhizome Mortality of the Invasive Fern Lygodium microphyllum (Schizaeles: Lygodiaceae)

Old World climbing fern, Lygodium microphyllum (Cav.) R. Br.; Schizaeles: Lygodiaceae), is among the most problematic invasive weeds in southern Florida, USA, where it smothers and displaces native vegetation. Chemical and mechanical control methods that target aerial fronds may not provide adequate control of L. microphyllum as underground rhizomes produce new fronds following treatment. Alternatively, biological control involves persistent feeding damage from introduced herbivores and may be an additional control measure for the management of the exotic weed. Herein, we hypothesized that high levels of persistent herbivory will reduce foliar biomass, kill underground rhizomes, and increase the number of other plant species. This hypothesis was tested over an 18 month period by placing 6 cages over L. microphyllum patches growing in a natural setting and repeatedly inoculating 3 of the cages with the Australian moth Austromusotima camptozonale (Hampson) (Lepidoptera: Crambidae) while the remaining 3 caged patches served as untreated controls. Growth of L. microphyllum was markedly reduced in herbivore treated patches versus untreated controls. Rhizome density and growth also decreased in herbivorycages, where rhizomes stopped producing fronds within 12 months and destructive sampling at 18 months showed complete rhizome mortality within these patches. The number of species within patches, however, remained similar among herbivory and control treatments. These findings represent the first evidence that chronic herbivory by arthropods can kill L. microphyllum rhizomes.