Old World climbing fern, is one of the worst environmental weeds of southern and central Florida, USA. The weed climbs over other plants, forming thick mats that block sunlight to native shrubs and trees. In the introduced range, Old World climbing fern invades much of the southern peninsula of Florida where cost-effective, sustainable control methods are needed. A potential biological control agent, the defoliating moth Lygomusotima stria was collected in Thailand and Singapore and was shown to be safe for release in the invaded range. Here, we report the results of greenhouse studies that examined the performance of the Lygomusotima stria larvae and their impact on the target weed when grown at a range of fertilizer and insect damage levels. The results indicate that larvae had greater survival when fed plants at the highest fertilizer level. Further, two generations of feeding by larvae decreased stem weights at the lowest fertilizer level and new shoot numbers. At higher fertilizer conditions, the plants were able to tolerate larva damage resulting in no significant changes in plant tissue allocations. By impacting stems and new shoots, these results suggest this insect will impede the ability of this weed to climb substrates especially in lower resource conditions.