Defoliation of the invasive fern Lygodium microphyllum by Neomusotima conspurcatalis: effects on plant performance across a range of light conditions.
Lygodium microphyllum (Cavanilles) R. Brown (Lygodiaceae) is an invasive climbing fern in south and central Florida. The fern is widespread in wet and mesic habitats, and thrives across a broad range of light environments. A classical biological control agent, Neomusotima conspurcatalis Warren (Lepidoptera: Crambidae) has been reared and released against L. microphyllum since 2008. Larvae of N. conspurcatalis consume L. microphyllum foliage; however, little is known about how this herbivory affects plant performance. We conducted a growth chamber experiment to examine the impact of larval defoliation (50% and 100%) on young L. microphyllum plants. Defoliation occurred under three different light regimes: (1) 80% shade with increased far-red/red light ratio; (2) 80% shade with no wavelength manipulation; (3) full light. Exposure to an elevated far-red/red light ratio elicited an increase in lateral branching in L. microphyllum. Plants in full light grew larger and recovered more quickly from herbivory than plants in the shade. Plant mortality resulting from defoliation was higher in shade treatments (27.5%) than in full sun (0%). While herbivory resulted in no plant mortality in full light, defoliation treatments (50% and 100%) did lead to significant reductions in shoot dry biomass across all light treatments. Root dry biomass was significantly reduced by herbivory treatments only in plants in full light. Our results suggest that a single defoliation event by N. conspurcatalis, alone, is unlikely to suppress L. microphyllum. However, the agent does have the potential to impact the weed at sites where the plant is exposed to additional stress factors such as unfavorable abiotic conditions, persistent herbivory, or when integrated with other management techniques.