Population establishment of and promising early results with the brown lygodium moth, Neomusotima conspurcatalis - a candidate biological control agent of Old World climbing fern, Lygodium microphyllum

Authors: Boughton, Anthony; Pemberton, Robert

Submitted to: Florida Exotic Pest Plant Council
Publication Type: Proceedings
Publication Acceptance Date: 3/16/2009
Publication Date: 5/28/2009
Citation: Boughton, A.J., Pemberton, R.W. 2009. Population establishment of and promising early results with the brown lygodium moth, Neomusotima conspurcatalis - a candidate biological control agent of Old World climbing fern, Lygodium microphyllum . Florida Exotic Pest Plant Council.

Interpretive Summary: Old World climbing fern, Lygodium microphyllum is one of the most serious invasive, weeds affecting southern and central Florida. Management of this weed using traditional strategies has proved difficult and expensive, with limited long-term success. In early 2008, a new biological control agent called the brown lygodium moth, Neomusotima conspurcatalis, was first released against infestations of L. microphyllum at three research sites in Jonathan Dickinson State Park in Martin County, Florida. Caterpillars of the moth feed on leaflets of the fern causing browning of leaves and defoliation of entire L. microphyllum plants. The life cycle of the moth from egg, through caterpillar and pupa to adult, takes about 30 days at 25 oC. Female moths lay an average of 136 eggs during their short lifespan. During the first 2-3 months after releases, life stages of the moth remained detectable at release sites and scattered, light-feeding damage was apparent. From 4-6 months, moth populations increased, and noticeable caterpillar feeding damage in the form of browned-out patches of L. microphyllum became apparent. By November 2008, 6-10 months after releases were made, substantial caterpillar-induced browning and defoliation of L. microphyllum was apparent at each of the three release sites, corresponding to an estimated total area of 14,900 square meters (3.7 acres). In addition, populations of the moth had radiated outwards from defoliated areas into surrounding areas and were feeding on lygodium within a larger area estimated at 36,000 square meters (8.9 acres). Within these active feeding zones, 4-second sweep net samples yielded an average capture of 11 adult moths per sample, while quadrat surveys yielded an average density estimate of 660 caterpillars per square meter of L. microphyllum. At release sites, linear cover of L. microphyllum along four 20-m vegetation transects decreased by an average of 61 percent, while quadrat-estimated lygodium area cover decreased by an average of 64 percent. At control sites where moths had not been released, linear cover of L. microphyllum increased by an average of 1 percent, while area cover increased by 7 percent. Although limited re-growth of L. microphyllum occurs from dormant lateral buds after caterpillar defoliation, female moths lay eggs on this re-growth. Preliminary observations suggest that the fern may not be able to recover from repeated rounds of defoliation. Although it is too early to declare this new agent a success, these findings are extremely encouraging and bode well for prospects of future biological control of L. microphyllum.

Technical Abstract: Old World climbing fern, Lygodium microphyllum is one of the most serious invasive, weeds affecting southern and central Florida. Management of this weed using traditional strategies has proved difficult and expensive, with limited long-term success. In early 2008, a new biological control agent called the brown lygodium moth, Neomusotima conspurcatalis, was first released against infestations of L. microphyllum at three research sites in Jonathan Dickinson State Park in Martin County, Florida. Caterpillars of the moth feed on leaflets of the fern causing browning of leaves and defoliation of entire L. microphyllum plants. The life cycle of the moth from egg, through caterpillar and pupa to adult, takes about 30 days at 25 oC. Female moths lay an average of 136 eggs during their short lifespan. During the first 2-3 months after releases, life stages of the moth remained detectable at release sites and scattered, light-feeding damage was apparent. From 4-6 months, moth populations increased, and noticeable caterpillar feeding damage in the form of browned-out patches of L. microphyllum became apparent. By November 2008, 6-10 months after releases were made, substantial caterpillar-induced browning and defoliation of L. microphyllum was apparent at each of the three release sites, corresponding to an estimated total area of 14,900 square meters (3.7 acres). In addition, populations of the moth had radiated outwards from defoliated areas into surrounding areas and were feeding on lygodium within a larger area estimated at 36,000 square meters (8.9 acres). Within these active feeding zones, 4-second sweep net samples yielded an average capture of 11 adult moths per sample, while quadrat surveys yielded an average density estimate of 660 caterpillars per square meter of L. microphyllum. At release sites, linear cover of L. microphyllum along four 20-m vegetation transects decreased by an average of 61 percent, while quadrat-estimated lygodium area cover decreased by an average of 64 percent. At control sites where moths had not been released, linear cover of L. microphyllum increased by an average of 1 percent, while area cover increased by 7 percent. Although limited re-growth of L. microphyllum occurs from dormant lateral buds after caterpillar defoliation, female moths lay eggs on this re-growth. Preliminary observations suggest that the fern may not be able to recover from repeated rounds of defoliation. Although it is too early to declare this new agent a success, these findings are extremely encouraging and bode well for prospects of future biological control of L. microphyllum.