Location: Invasive Plant Research Laboratory
2011 Annual Report
Exotic invasive weeds from overseas pose a severe threat to native plants and ecosystems within the United States. The mission of USDA-ARS Invasive Plant Research Laboratory is to find environmentally friendly, biologically based strategies for long-term sustainable management of invasive weeds within the United States. Old World climbing fern, Lygodium microphyllum, is recognized as one of the three most damaging invasive weeds currently impacting natural ecosystems in Florida. The research described below supports the mission of the national program by furthering progress towards sustainable management of L. microphyllum. Populations of the brown lygodium moth, Neomusotima conspurcatalis, have survived into their fourth year at release sites in southeast Florida. As moth populations have fluctuated over recent years, there have been corresponding reciprocal changes in ground cover of L. microphyllum. When populations of the moth decline, reductions in feeding by caterpillars allow re-growth of L. microphyllum. When large populations of the moth are present at sites, defoliation by caterpillars causes considerable reductions in ground cover of L. microphyllum. Data collected along 12 transects in March 2011, showed that less of the weed was present than before the agent was released in 2008. Surveys during fall of 2010 revealed average densities of 200-800 caterpillars per square meter of lygodium foliage, but on occasion peak densities as high as 16,000 caterpillars per square meter. At these densities caterpillars cause complete defoliation and significant suppression of lygodium. Six species of parasitic wasp have been reared from N. conspurcatalis caterpillars. Across, 22 collections of moth caterpillars made between 2008 and 2010, the overall rate of parasitism by wasps was 10 percent. A new colonization effort with the lygodium moth, Austromusotima camptozonale, was initiated in summer 2010. During fall 2010, 18,000 caterpillars were distributed in open releases, but there was no evidence of population establishment. During spring 2011, 24,000 caterpillars were released into large field cages in efforts to improve adult mating, prior to release of moths from cages. Although survival of lab-reared caterpillars was much improved inside the cages, there was no evidence that persistent moth populations had established or were increasing around the field cages, suggesting that predation remains a problem outside the rearing cages.