Preferential consumption of fertile fronds by Neomusotima conspurcatalis on Lygodium microphyllum: Reducing propagule pressure of Florida's worst weed

Background/Question/Methods

Old World climbing fern, Lygodium microphyllum (Cav.) R. Br (Polypodiales: Lygodiaceae), an invasive weed, is widespread and expanding its range throughout wetland and mesic habitats in Florida. Lygodium microphyllum degrades critical ecosystem services and habitats of rare and endangered species throughout Florida, especially within wilderness areas in Big Cypress National Preserve and Everglades National Park.  Lygodium microphyllum spreads into isolated sites by vast production of self-compatible airborne spores. Due to the remote nature of the infestations, poor herbicide performance and collateral damage from spraying and fire, traditional means of removal are costly and cumbersome.  Beginning in 2004, biological control agents were released to provide consumer control to these populations.  One of these agents, Neomusotima conspurcatalis Warren (Lepidoptera: Crambidae), released in 2008 and thereafter, has successfully established in multiple sites. As part our investigations looking at the effects of the biocontrol agent on L. microphyllum, we tested the feeding preference of N. conspurcatalis larvae on reproductive (i.e. fertile) fronds and sterile fronds using choice and no-choice feeding trials. First instar larvae were transferred to wetted filter paper at the midpoint between same-sized leaves and followed until they pupated. Leaves were changed daily, photographed and weighed as wet weight.  Leaf preference was determined using χ² and one-way ANOVA. Digested spores were then extracted from caterpillar frass and plated to determine germination rates.  

Results/Conclusions

First and second instar larvae consumed significantly more fertile fronds than sterile fronds in choice trials (weight: P < 0.01, area: P < 0.01). In no choice trials, larvae did not consume significantly different leaf area or mass. Later instars consumed significantly more total area, but did not display significant preference differences in choice or no-choice trials. Digested spores produced only two prothalli, while undigested spores of the same volume produced thousands. Future investigations include quantifying aerial spore density in sites where the biocontrol moths have established and quantifying site-scale consumption. Large established populations of N. conspurcatalis may confer some control of L. microphyllum by reducing the now massive spore rain.