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Research Project: Identification, Evaluation, and Implementation of Biological Control Agents for Invasive Weeds of Southeastern Ecosystems

Location: Invasive Plant Research Laboratory

2018 Annual Report

Our goal is the environmentally safe, sustainable suppression of exotic invasive species that threaten natural, agricultural, and urban ecosystems in the United States with an emphasis on weeds. Objective 1: Develop biological control programs for invasive weeds threatening the Everglades, and similar southeastern ecosystems, through the discovery, identification, efficacy testing, safety testing, release, and evaluation of new biological control agents. Sub-objective 1.1. 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. Sub objective 1.2. Conduct faunistic and floristic inventories to discover natural enemies that may serve as biological control agents for targeted weed species. Sub-objective 1.3. Conduct risk analysis to determine environmental safety of new and existing potential biological control agents for weeds. Objective 2: Improve current biological control programs of invasive weeds in the Everglades, and similar southeastern ecosystems, by developing integrated weed management strategies.

As described above, biological control research progresses in a stepwise fashion and our objectives detailed below are interconnected and flexible. The objectives are intentionally general to encompass the various weed targets and natural enemies that are currently under investigation, as well as those that may be added during the life of the research project. The first objective contains three sub-objectives that address the ecology of the weed, the discovery of potential agents, and the determination of their safety for release. The second objective focuses on the integration of biological control with other methods. A Milestone Table is prepared for each sub-objective and provides details on the tested hypotheses, scientific assignments, annual goals (milestones), and expected products of the research.

Progress Report
Melaleuca quinquenervia ('melaleuca') is a tall evergreen tree that was introduced into southern Florida in 1886 and by 1994 had infested about 800 square miles. Infestations of melaleuca outcompete native plants, eliminate animal habitats, increase fires, disrupt nutrient storage and cycling, and affect human health. Classical biological control programs at the USDA-ARS Invasive Plant Research Lab (IPRL) in Fort Lauderdale, Florida, have transformed this plant into a less invasive form which is now much easier to control. The latest prospective biological control agent is the galling fly Lophodiplosis indentata which is now nearing completion of host range testing in quarantine. A petition for regulatory consideration is being prepared for submission to the Technical Advisory Group (TAG) for the biological control of weeds. Old World climbing fern, Lygodium microphyllum, ('lygodium') is a climbing fern native to tropical Asia that has invaded Florida and is smothering tree islands, cypress domes, pine woodlands, and tropical hammocks in the Everglades. This fast-growing fern produces enormous numbers of spores that can travel long distances on the slightest breeze and, as a result, this weed continues to expand its range in Florida. To date, IPRL has developed and established a moth and a mite whose ranges continue to increase across Florida. An additional 506,654 brown lygodium moths (Neomusotima conspurcatalis) and 212,172 mites (Floracarus (F.) perrepae) were released at remote and key conservation areas throughout central and south Florida. Outbreaks of the moth continue to be observed in multiple locations leading to browning out of lygodium populations. ARS scientists continue to learn more about the biology of F. perrepae to optimize rearing and release methods. The mite is challenging to establish but preliminary data indicates it can cause a four-fold reduction in rachis growth rates compared to undamaged rachises. Integrated pest management programs are being developed to determine how to effectively combine biological control with herbicide applications and prescribed burns to manage lygodium. New biological control agents for lygodium continue to be developed including two leaf feeding moths, a sawfly, and four species of stem borers. The moth, Lygomusotima (L.) stria, shows high specificity after quarantine testing against 69 non-target plants. Multigenerational tests are underway for L. stria on Lygodium palmatum and the invasive Lygodium japonicum, whose range overlaps those of L. palmatum and Lygodium microphyllum. Similar testing is underway for the lygodium sawfly, Neostrombocerus albicomus, in order to quantify its ability to sustain a population on a Caribbean species, Lygodium volubile. ARS scientists from IPRL received shipments of the newly described lygodium stem borer, Siamusotima disrupta, from Hong Kong and are developing rearing methods for this poorly known species so that it can be tested. Additional individuals of the noctuid moth Callopistria sp. were also received from Hong Kong. A colony was established and host-range testing has been conducted with 25 non-target plant species. This insect feeds voraciously and early results indicate that is a lygodium specialist. Chinese tallow, (Triadica sebifera), is an invasive tree that has invaded about 500,000 acres of southern U.S. forests where it reduces timber harvests and wildlife habitat. The TAG approved the release of the first biological control agent of Chinese tallow, the flea beetle (Bikasha collaris). A TAG petition for a second biological control agent, the moth Gadirtha fusca, was submitted after research showed this species to be highly specific to Chinese tallow. Other potential agents that might be useful include a new species of galling midge, possibly in the Lasioptera genus, which was introduced into quarantine. Currently IPRL scientists are attempting to establish a colony of this midge to begin testing for safety and suitability. Additional herbivore pressure from biological control agents is needed to reduce the performance of this invasive weed. Rhodomyrtus tomentosa (downy rose myrtle) is a tall shrub that invades biologically important habitats including the Everglades in Florida, and also forests, grasslands, and pastures in Hawaii. Downy rose myrtle thrives in forest understories, preventing natural fire events, disrupting nutrient cycles while outcompeting native plants for light and nutrients. Biological control may offer a solution to this problem and surveys for potential agents have been conducted in mainland China, Hong Kong, Sri Lanka, and Thailand. Several insects found during these surveys were imported into Fort Lauderdale quarantine for further testing. These included species of the stem boring moth Casmara sp. and a fruit-feeding moth Mesophelps pos. albilinella. Although testing is not yet completed, these species may prove to be unsuitable because the initial data suggests they are not specific enough to use safely against this weed. Brazilian peppertree, Schinus terebinthifolia, is one of the worst invasive species of southern Florida, occupying more area than melaleuca and lygodium combined. A release permit for a thrips biological control agent, Pseudophilothrips ichini, is expected in summer 2018. Additional Brazilian collections yielded a defoliating caterpillar species from a complex of Paectes spp. The adults that emerged from these collections have been prepared and are undergoing morphological and DNA molecular determinations. These new species from these collections will be examined for their suitability as biological control agents of Brazilian peppertree. Waterhyacinth, Eichhornia crassipes, is considered the worst floating aquatic weed on earth, damaging ecosystems and entire economies of developing countries. The planthopper Megamelus (M.) scutellaris was the first new biological control agent released against waterhyacinth in more than 30 years and is now widely established in southern and northern Florida locations. A total of 377, 275 M. scutellaris were released to date in 13 sites in Florida during FY 18. The agents have dispersed up to 6.4 km from release sites on Lake Okeechobee, including through areas sprayed with herbicides. A new species of planthopper (Lepidelphax pistae) was collected in Argentina, colonized in Fort Lauderdale quarantine, and is currently being tested to determine its environmental safety as a biological control agent for waterlettuce, Pistia stratiotes, another serious floating aquatic weed. To date, the planthopper has been tested in Fort Lauderdale quarantine against 42 non-target plants and has shown a high degree of fidelity to waterlettuce. Quarantine based studies on its impact on waterlettuce and its development at different temperatures are continuing. Air potato (Dioscorea bulbifera) vine is one of the most invasive climbing vines of exotic origin. It has spread throughout public and private forested properties in all 67 Florida counties and in other adjacent states. IPRL has developed two biotypes (Nepalese and Chinese) of a biological control beetle Lilioceris cheni that feeds only on air potato leaves and vine-tips. To date during FY 18, IPRL has distributed 29,222 L. cheni beetles to 205 locations in southern Florida. In addition, ARS scientists from IPRL completed a 5 year field evaluation in Florida that documented a 73% decline in vine coverage, a 95% reduction in bulbil production, and a 62% increase in native species as the habitat recovered. Host specificity testing in quarantine of another agent, Lilioceris egena, was completed and a TAG petition was submitted and approved with minimal comments. Consideration for a release permit now moves to APHIS and U.S. Fish & Wildlife. Earleaf acacia (Acacia auriculiformis) is a fast-growing, evergreen tree that invades agricultural and natural areas of Florida. A study was conducted to determine the feasibility for biological control of earleaf acacia. This study discovered new potential agents in the plant’s native range of Australia and compiled a test plant list following phylogenetic characterization of related taxa. Among the Australian discoveries were seed feeding weevils (Melanterius spp). Additionally, both larvae and adult defoliating chrysomelid beetles (Calomela sp. and pos. Dicranosterna sp.) were discovered along with seed feeding Bruchidae, foliage feeding Eriophyidae mites, leaf tying larvae (Lepidoptera: Gracillariidae), and two species of mirid bugs, including Riptortus sp. Foreign surveys for additional agents is ongoing.

1. New biological control agent for Brazilian pepper. The thrips biocontrol agent Pseudophilothrips ichini recently obtained a letter of concurrence from U.S. Fish & Wildlife that stated it was not likely to adversely affect any threatened or endangered organisms and thus is cleared for public comment as part of the permitting process. Thrips feeding under greenhouse conditions reduced Brazilian pepper seedling growth by 80%. When the release is approved this summer, this biological control agent may provide land managers and farmers with a cost effective means of controlling Brazilian pepper by reducing the current and expensive reliance on herbicidal control.

2. New biological control agent for Chinese tallow. ARS scientists in Fort Lauderdale, Florida, completed host range testing of the moth Gadirtha fusca and found this insect to be safe for release. A Technical Advisory Group (TAG) petition for general release was prepared and submitted. When the release is ultimately approved, this biological control agent may provide land managers and farmers with a cost effective means of controlling Chinese tallow by reducing the current reliance on herbicidal control.

3. New biological control agent for air potato. ARS scientists in Fort Lauderdale, Florida, completed host range testing for a new biological control agent, the beetle Lilioceris egena, that eats the reproductive bulbils (‘potatoes’) associated with air potato. A Technical Advisory Group (TAG) petition was submitted and subsequently received a recommendation for release with minimal comments from committee members.

4. New insights on indirect effects of biological control by ARS scientists in Fort Lauderdale, Florida. A NIFA funded research project examining the indirect effects of biological control found no evidence that a biological control agent negatively influences other native insects in the same aquatic habitat.

Review Publications
Minteer, C., Smith, M., Lake, E.C., Pokorny, E.N. 2018. Teaching complex ecological concepts through a demonstration garden Biodiversity, invasions and conservation in practice. The American Biology Teacher. 80(5):346-352.
Pile, L., Wang, G., Stoval, J., Siemann, E., Wheeler, G.S., Gabler, C.A. 2017. Mechanisms of Chinese tallow (Triadica sebifera) invasion and their management implications– A review. Forest Ecology and Management. 404:1-13.
Lake, E.C., Minteer, C.R. 2018. A Review of the Integration of Classical Biological Control with other Management Techniques to Manage Invasive Weeds in Natural Areas and Rangelands. BioControl. 63:71-86.
Wheeler, G.S., Hight, S.D., Wright, S.A. 2017. Impact of field densities of the naturalized defoliator Caloptilia triadicae on the invasive weed Chinese tallowtree. Environmental Entomology. 46(6):1305–1312.
Tipping, P.W., Martin, M., Rayamajhi, M.B., Pratt, P.D., Gettys, L. 2018. Combining biological and mechanical tactics to suppress Melaleuca quinqueneria. Biological Control. 121:229-233.
Tipping, P.W., Gettys, L., Minteer, C., Foley, J., Sardes, S. 2017. Herbivory by biological control agents improves herbicidal control of waterhyacinth (Eichhornia crassipes). Invasive Plant Science and Management. 107:41-49.
Tipping, P.W., Martin, M., Gettys, L. 2017. Biological control increases the susceptibility of Melaleuca quinquenervia to fire. Biocontrol Science and Technology. 27(8):1014-1017.
Jones, I.M., Kopture, S. 2017. Dead land walking: the value of continued conservation efforts in south Florida’s imperiled pine rocklands. Biodiversity and Conservation Journal.
Burckhardt, D., Cuda, J., Diaz, R., Overholt, W., Prade, P., De Queiroz, D., Vitorino, M., Wheeler, G.S., Williams, D. 2018. Taxonomy of the Brazilian peppertree psyllids (Hemiptera: Calophyidae: Calophya). Florida Entomologist. 101(2):178-188.
Jones, I.M., Koptur, S., Pena, J. 2017. Exploring whether and how ants affect reproductive fitness in Senna mexicana var. chapmanii. Florida Entomologist. 100(3):539-545.
Smith, M., Mack, R.N. 2018. Apparent tolerance of low water availability in temperate Asian bamboos. Journal of Environmental Horticulture. 36(1):7-13.
Smith, M., Overholt, W.C., Lake, E.C., Diaz, R., Manrique, V., Hight, S.D., Rohrig, E., Minteer, C., Wheeler, G.S., Rayamajhi, M.B., Bowers, K.E., Kerr, C. 2018. Changes in latitude: overwintering survival of two Lilioceris cheni(Coleoptera: Chrysomelidae) biotypes in Florida. Biocontrol Science and Technology. 28(3):293-306.
Lake, E.C., Smith, M., Rayamajhi, M.B., Pratt, P.D., Dray Jr, F.A. 2018. Minimum threshold for establishment and dispersal of Lilioceris cheni (Coleoptera: Chrysomelide): a biological control agent of Dioscorea bulbifera. Biocontrol Science and Technology. 28(6):603-613.