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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

2016 Annual Report


1a. Objectives (from AD-416):
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.


1b. Approach (from AD-416):
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.


3. Progress Report:
Melaleuca quinquenervia ('melaleuca') is a tall evergreen tree that was introduced into southern Florida in 1886 and by 1994 had infested about 200,000 ha. Infestations of melaleuca outcompete native plants, eliminate animal habitats, increase fires, disrupt nutrient storage and cycling, and affect human health. Classical biological control has played a pivotal role in preventing re-infestation of cleared areas and slowing the rate of infestation into new ones. Numerous field studies, including a 16 year old field assessment, demonstrated the degree to which this weed has been suppressed thereby allowing native plant species to re-colonize areas formerly dominated by this weed. New species were added to the test plant list to accommodate new requirements of U.S. Forestry and Wildlife Service (USFWS) to test not only threatened and endangered plant species, but also the host plant species of threatened and endangered insects. Old World climbing fern, Lygodium (L.) 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. Classical biological control is integral to management efforts to halt the march of this weed. To date, the laboratory has developed and established a moth and a mite whose ranges continue to increase across Florida. An additional 211,322 moths (Neomusotima conspurcatalis) and 56,475 mites (Floracarus perrepae) were released at remote and key conservation areas throughout central and south Florida. Phylogenetic research is ongoing to find a better match between lygodium and the mite. Once the work is complete, an additional haplotype(s) will be imported to attack lygodium in Florida that is resistant to the mite haplotype that is currently available. Integrated pest management programs are being developed to better integrate biological control with herbicides and prescribed burns. New biological control agents for lygodium continue to be developed including a leaf feeding moth, a sawfly, and four species of stem borers. The moth, Lygomusotima stria, shows high specificity after quarantine testing against 57 non-target plants. Multigenerational tests are underway for L. stria on L. palmatum and the invasive L. japonicum, whose range overlaps those of L. palmatum and L. 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. Scientists from the laboratory received shipments of the newly described lygodium stem borer, Siamusotima disruptus from Hong Kong and are developing rearing methods for this poorly known species so that it can also be tested. Several individuals of the noctuid moth Callopistria sp. were received from Hong Kong. A colony has been established and host-range testing has begun. Additional biological control agents are needed to decrease the growth and reproduction of this invasive weed; surveys are ongoing in the native range. 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. Quarantine testing was completed of the first biological control agent of Chinese tallow, the flea beetle (Bikasha collaris). These results showed that the flea beetle was safe to release as it could only complete its life cycle on the weed Chinese tallow. Research is nearly complete on the second biological control agent, a moth Gadirtha fusca which shows this species is also highly specific to tallow. Other potential agents that might be useful for the biological control of this tree include a new species of galling midge, possibly in the Lasioptera genus, which was introduced into quarantine. Rhodomyrtus (R.) 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 but prevents natural fire events and disrupts nutrient cycles while outcompeting native plants for light and nutrients. ARS scientists from Ft. Lauderdale, Florida, along with cooperators from the CSIRO Australian Biological Control Laboratory, recently explored areas of Singapore, Malaysia, and Hong Kong to survey and collect additional natural enemies of R. tomentosa. Several insects species were collected and sent back to the Gainesville, Florida, quarantine laboratory for colonization and testing. These included species of an unknown tip binding moth, Strepsicrates sp., a stem boring moth Casmara sp., a fruit-feeding moth Mesophelps pos. albilinella, and a defoliating beetle Cryptocephalus sp. Host range testing on Strepsicrates and Cryptocephalus ruled these two species out based on their broad host affinity. Testing continues for Mesophleps and Casmara, though both show initial indications of broad host specificity. Brazilian peppertree, Schinus terebinthifolia, is one of the worst invasive species of south Florida, occupying more area than the weeds Melaleuca and Lygodium combined. Host testing of the thrips Pseudophilothrips ichini, an agent developed for biological control of Brazilian peppertree, was completed and petitioned for release. The technical advisory committee (TAG) review was completed and passed a recommendation to USDA/APHIS for its release. 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 suitablity 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 considered established in southern and northern Florida locations. A total of 580,261 M. scutellaris have been released in 5 counties in Florida during FY 2016. A second year of cooperative research with the University of Florida confirmed the utility of combining biological control agents with lower rates of herbicides to achieve equal or higher levels of control of waterhyacinth. A new species of planthopper (Lepidelphax pistae) has been collected in Argentina, colonized in Ft. Lauderdale, Florida, 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 plant hopper has been tested in Ft. Lauderdale, Florida, quarantine against 65 non-target plants and has shown a high degree of fidelity to waterlettuce. In addition, plants were severely damaged following exposure to this potential agent for 60 days. Air potato, Dioscorea bulbifera, is an aggressive climbing vine which smothers native vegetation as it spreads rapidly throughout forested areas. Biological control is the most sustainable tactic available to control this weed and an effective agent, the leaf-feeding beetle Lilioceris cheni, was developed and released in Florida by the laboratory. Large beetle populations have built up in the field and are causing premature die back of air potato vines and reducing tuber production in some sites. An additional 64,726 beetles were released at 289 sites to facilitate establishment of new populations and to augment depleted populations. Data from five long-term research sites showed up to 39% and 67% reduction of air potato vines and propagative units (bulbils), respectively. Host specificity testing in quarantine of another agent, Lilioceris egena, is 95% complete with results showing such close fidelity of this beetle to its host that it only produces eggs on the plant’s storage organs (aerial bulbils and underground tubers). A series of hybridization experiments between the Chinese and Nepalese biotypes of L. cheni detected no hybrid depression. As a result, field releases and research of the Nepalese biotype have commenced. 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).


4. Accomplishments
1. Integrated control of waterhyacinth. This weed is considered the worst floating aquatic weed on earth, found on every continent except Antarctica. ARS researchers in Ft. Lauderdale, Florida, demonstrated that attack by biological control agents (insects) weakened waterhyacinth to the extent that lower rates of herbicides were as effective as the higher operational rates. Low rates of 2,4-D without insects reduced waterhyacinth by only 4.5% because of regrowth. High rates of 2,4-D without insects reduced the weed by 42.9%. But when the biological control agents were combined with both the low and high rates of herbicide, waterhyacinth was reduced by 99.8 and 100%, respectively. This finding indicates that the amount of herbicides applied to fresh water ecosystems to control waterhyacinth could be reduced without sacrificing efficacy by taking in account the impact of the biological control agents.

2. Augmenting biological control of waterhyacinth. More efficient use of the new ARS rearing facility in Ft. Lauderdale, Florida, along with increases in rearing optimization, production, and release methods for the planthopper Megamelus (M.) scutellaris resulted in a 48% increase in deployed agents from FY 2015 (580,260 M. scutellaris released at 55 locations in 5 counties in Florida). The stress inflicted on waterhyacinth by biological control agents like M. scutellaris makes the plant more susceptible to other control methods.

3. New biological control agent for Chinese tallow. Chinese tallow (Triadica sebifera) is an invasive weed that infests natural and agricultural areas of the Gulf states from Texas to South Carolina. ARS scientists in Ft. Lauderdale and Gainesville, Florida, completed host range testing of the flea beetle, Bikasha collaris and found this insect to be safe for release. A petition for general release has been submitted to the USDA/APHIS Technical Advisory Group (TAG) for the Biological Control of Weeds. If the release is 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.

4. Early production and releases of air potato control beetles. ARS scientists at Ft. Lauderdale, Florida, were able to produce more beetles in early growing season compared to previous years by keeping Lilioceris cheni colonies active during the dormant winter through improvements in plant and insect production methods. This has allowed beetle releases as early as March instead of June. This is expected to accelerate early vine mortality and reduce bulbil production in beetle released areas.


5. Significant Activities that Support Special Target Populations:
ARS scientists and technicians from Ft. Lauderdale, Florida, met land managers and private land owners over 50 different occasions at parks, natural areas, and private lands infested with air potato and, in groups or individually, provided beetles and advise on the use of biological control tactics in air potato management.


Review Publications
Wheeler, G.S., Silverson, N., Dyer, K.G., Mckay, F. 2016. Brazilian collections and laboratory biology of the thrips Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae): a potential biological control agent of the invasive weed Brazilian peppertree (Sapindales: Anacardiaceae). Florida Entomologist. 99(1):6-11.
Madeira, P.T., Hill, M.P., Dray Jr, F.A., Coetzee, J.A., Paterson, I.D., Tipping, P.W. 2016. Molecular identification of Azolla invasions in Africa: The Azolla specialist, Stenopelmus rufinasus proves to be an excellent taxonomist. South African Journal of Botany. 105:299-305.
Lake, E.C., Gates, M.W., Smith, M., Witkus, G.L., Pratt, P.D. 2015. First report of an egg parasitoid reared from Neomusotima conspurcatalis (Lepidoptera: Crambidae) a biological control agent of Lygodium microphyllum (Schizaeales: Lygodiaceae). Florida Entomologist. 98(4)1244:1246.
Madeira, P.T., Facey, J., Pratt, P.D., Maul, D., Wheeler, G.S. 2016. Are three colonies of Neostromboceros albicomus, a candidate biological control agent for Lygodium microphyllum, the same host biotype? Biocontrol Science and Technology. 26(3):440-445.
Pratt, P.D., Herdonica, K., Valentine, V., Makinson, J., Purcell, M., Mattison, E.D., Rayamajhi, M.B., Raghu, S., Moran, P.J. 2016. Development rate, consumption and host specificity of Carea varipes (Lepidoptera: Nolidae). Annals of the Entomological Society of America. 109(4):513-517. doi: 10.1093/aesa/saw021.
Minteer, C., Kring, T.J., Wiedenmann, R.N. 2016. Larinus minutus (Coleoptera: Curculionidae) and Urophora quadrifasciata (Diptera: Tephritidae), evidence for interaction and impact on spotted knapweed in Arkansas. Environmental Entomology. 43:3,658-662.
Tipping, P.W., Martin, M., Pratt, P.D., Wheeler, G.S., Gettys, L. 2016. Response of two chemotypes of Melaleuca quinquenervia (Myrtales: Myrtaceae) saplings to colonization by specialist herbivores. Florida Entomologist. 99:77-81.
Duncan, J., Steininger, S., Wright, S.A., Wheeler, G.S. 2016. Host range of Caloptilia triadicae (Lepidoptera: Gracillariidae): an adventive herbivore of Chinese tallowtree (Malpighiales: Euphorbiaceae). Florida Entomologist. 99(1):142-145.
Overholt, W.A., Rayamajhi, M.B., Rohrig, E., Hight, S.D., Dray Jr, F.A., Lake, E.C., Smith, M., Hibbard, K., Bhattarai, G., Bowers, K.E., Poffenberger, R., Clark, M., Curry, B., Stange, B., Calise, E., Wasylik, T.K., Martinez, C.M., Leidi, J.G. 2016. Release and distribution of Lilioceris cheni (Coleoptera: Chrysomelidae), a biological control agent of air potato (Dioscorea bulbilfera: Dioscoreaceae), in Florida. Biocontrol Science and Technology. 26:1087-1099.
Hough-Goldstein, J., Lake, E.C., Shropshire, K.J., Moore, R.A., D'Amico, V. 2016. Laboratory and field-based temperature-dependent development of a monophagous weevil: implications for integrated weed management. Biological Control. 92:120-127.
Wheeler, G.S., Mattison, E.D., Metz, M., Pratt, P.D., Purcell, M. 2016. Host range of the defoliator Strepsicrates sp. is too broad for biological control of the invasive weed Rhodomyrtus tomentosa. Biocontrol Science and Technology. 26:861-865.
Tipping, P.W., Martin, M., Nimmo, K., Smart, M., Wear, E. 2016. Food web associations among generalist predators and biological control agents of Melaleuca quinquenervia. Biological Control. 52-58 doi 10.1016/J.biocontrol.2016.06.008.
Fung, J., Wheeler, G.S. 2016. Life history and host range of Oxydia vesulia transpeneus, an unsuitable biological control agent of Brazilian peppertree. Biocontrol Science and Technology. 26(3):298-304.