Location: Invasive Plant Research Laboratory2011 Annual Report
1a. Objectives (from AD-416)
1. As new high-priority invasive species are detected in the U.S., conduct feasibility studies to determine their suitability for biological control. 2. Elucidate the ecology and population dynamics of targeted weeds and their potential insect and pathogen biological control agents, and investigate the impact of weed suppression on community and ecosystem structure and function. 3. Conduct faunistic and floristic inventories to discover natural enemies that may serve as biological control agents for target weeds including, but not limited to Brazilian pepper, lygodium, downy rose myrtle, skunk vine and Chinese tallow. Additional biological control agents will be sought for species for which some control has been achieved, including melaleuca. 4. Conduct risk analysis to determine environmental safety of new and existing potential biological control agents for weeds such as air potato, melaleuca, Brazilian pepper, lygodium, downy rose myrtle, Chinese tallow, waterlettuce and skunk vine. 5. Release, establish, evaluate efficacy, and corroborate environmental safety of approved biological control agents and develop and distribute the technology to customers in order to expedite their adoption and deployment.
1b. Approach (from AD-416)
Survey foreign nations for potential biological control agents, determine host specificity of candidate species, release approved agents into natural and agricultural ecosystems, and evaluate influence of agents on target weed and nontarget species population dynamics. Study molecular genetics of target weeds. Study their roles as insect feeding attractants/deterrents, effects on biological control agents' nutritional and reproductive physiology, and possible use in host specificity protocols. Study biological control agents' impact on competition between target weeds and non-target native plants. Identify ways to incorporate biological control agents into IPM strategies. Survey water bodies in Connecticut for presence of troublesome aquatic weeds.
3. Progress Report
An experiment with waterhyacinth, employing two weevils released as its biocontrols and five plant fertility levels, shows that biocontrol effectiveness is context specific. The first new biocontrol agent in 30 years (Megamelus scutellaris) targeting waterhyacinth was released in Florida, Texas, Louisiana, California, and Mississippi. Surveys of invaded sites in extreme southeastern Florida show varying densities of biocontrol insects (weevil, psyllid, cecid) and an adventive foliar rust fungus, all of which damage melaleuca trees. Studies at long-term (15-yr) plots show declining melaleuca stand density leads to significant return of native plants such as sawgrass, dahoon holly, myrcine, wax myrtle and others. There is significant reduction in the number of trees producing seeds, due to continual damage of new foliage and associated lessened flower production. Surveys of fanwort produced 49 fungal isolates from plants in Texas, and plant samples in Florida for DNA analysis. Surveys show that the Melaleuca stem gall fly is persisting and dispersing (average 6 km per year) at all 24 initial release sites. Research shows that Brazilian peppertree stem diameter accurately predicts number of leaves and fruits. This nondestructive method of assessing plant biomass and growth, together with baseline data regarding plant phenology (leaf lifespan and litterfall dynamics) are needed to measure the impact future biological control agents have on plant performance. The following herbivores with potential as biocontrol agents are being assessed in quarantine: stem-boring moths on skunkvine (Paederia foetida), Old World climbing fern (Lygodium microphyllum), and Brazilian peppertree (Schinus); a flea beetle and moth on Chinese tallow tree (Triadica sebifera); an inchworm, leaf blotching moth, thrips, psyllid, and a new wasp and caterpillar (both gall-forming) on Schinus; a plant-feeding staphylinid beetle and eriophyiid mite on Paederia; a gall fly and a weevil on Melaleuca; a defoliating owlet moth on Triadica; an ermine moth on Rhodomyrtus; and a defoliating moth and sawfly on Lygodium. The Schinus leaf blotchers and inchworm proved not to be specialists on Schinus, and several of the species have proven difficult to colonize. Permits were obtained for release in the U.S. of the Asian leaf-feeding beetle Lilioceris cheni which is a specialist on air potato, Dioscorea bulbifera. Releases of two approved Lygodium biocontrols (Neomusotima conspurcatalis and Austromusotima camptozonale) continued, as did field evaluations of established populations of the former. Molecular genetic techniques were used to clarify the taxonomy of Cabomba and relatives of Schinus, to identify fungal pathogens from Cabomba, to confirm identities of Dioscorea plants from which Lilioceris beetles were collected in China, and to confirm that the beetles from China were the same biotype of Lilioceris as beetles from Nepal used in earlier host range testing.
1. First biocontrol agent against air potato approved for release. Researchers at the ARS Invasive Plant Research Laboratory (IPRL) in Fort Lauderdale, Florida, are tasked with locating, vetting the host fidelity of, implementing, and assessing the efficacy of highly specific natural enemies for use against troublesome weeds that have invaded agricultural or conservation lands. IPRL scientists recently received regulatory approval from USDA, APHIS and the state of Florida to release the Asian leaf beetle Lilioceris cheni as a biological control of the invasive air potato vine (Dioscorea bulbifera). Air potato is native to Asia and Africa, but has made its way to the U.S. where it occurs in Florida, Texas, Hawaii, Louisiana, Mississippi, and Puerto Rico. It is most extensively distributed in Florida where it occurs in 34 counties throughout the state, including many infestations within the historic boundaries of Florida’s unique Everglades ecosystem. Infestations cover fences, climb over trees and shrubs, and can produce a thick canopy reminiscent of kudzu, shading out and killing native vegetation. Release of Lilioceris promises to help reduce deleterious impacts of air potato on conservation lands in the U.S. Gulf Coast, and permit recovery of native species excluded by this weed.
Rayamajhi, M.B., Pratt, P.D., Center, T.D., Van, T.K. Exotic tree leaf litter accumulation and mass loss dynamics compared with two sympatric native species in south Florida, USA. European Journal of Forest Research. 129:1155-1168. 2010.