Location: Invasive Plant Research Laboratory
2023 Annual Report
Objectives
The objectives of this project plan are to develop environmentally safe, self-sustaining methods for the management of invasive weeds of exotic origin that threaten ecologically sensitive aquatic and terrestrial ecosystems of the United States, with a focus on the southeastern region. The following four objectives are relevant to the NP 304 Action Plan, Component 2 – Weeds; Problem Statement 2B: Biological control and ecosystem research and Problem Statement 2C: Integrated approaches to weed management.
Objective 1: Identify and prioritize invasive weeds that negatively affect ecologically sensitive terrestrial and aquatic ecosystems of the southeastern United States. [C2, PS 2C]
Objective 2: Survey native habitats of the candidate weeds in their geographical areas of origin for potential biological control agents. Acquire and characterize biological control agents and conduct thorough host-specificity tests informed by molecular phylogeny to determine fundamental host range. [C2, PS 2B]
Objective 3: Deploy APHIS-approved biological control agents and evaluate their efficacy by documenting impacts to target weed populations. [C2, PS 2B]
Objective 4: Evaluate impact of biological control projects on native plant diversity, invertebrate food webs, and plant disease dynamics at community and landscape levels. Develop integrated methods to improve overall weed management efforts. [C2 PS 2B and 2C]
Approach
Biological control research is a dynamic process and thus the proposed research objectives detailed below are often interconnected, flexible, with feedback loops. Although we have presented discrete research objectives in a generalized fashion to accommodate the various weed targets and their natural enemies which are currently under investigation, some may be removed and others added during the life of the proposed 5 yr research project. A Milestone Table has been prepared for each objective which details the hypotheses, scientific assignments, annual goals (milestones), and expected outcomes of the given research activities
Progress Report
Invasive weeds are one of the leading causes of habitat loss and dramatically disrupt ecosystem services. In sensitive ecosystems such as Florida’s Everglades, the harms brought about by invasive species can exacerbate stressors caused by climate change and development, leading to species declines and even extinctions. Biological control is one of the most cost effective means of controlling invasive species with an expected return on investment in excess of 35:1 in successful programs. The Invasive Plant Research Laboratory (IPRL) in Fort Lauderdale, Florida, has a history biological control programs that have successfully reduced cover, reproduction and negative impacts of invasive species (e.g., melaleuca, air potato, alligator weed, common salvinia, etc.). The following is an account of our progress towards restoring natural areas, including America’s largest wetland, from the impacts of harmful plant invasions.
Air potato (Dioscorea bulbifera) vine has spread throughout public and private forested properties in all 67 Florida counties and adjacent states. The Invasive Plant Research Laboratory in Fort Lauderdale, Florida, developed two genotypes (Nepalese and Chinese) of the leaf beetle Lilioceris cheni whose feeding reduces air potato growth and reproduction. Focus of the project shifted over the past two FYs to another beetle, Lilioceris egena, which feeds and develops on the vegetative propagules (called bulbils) of air potato. Mass rearing efforts during FY’23 produced over 40,000 beetles for release in 219 field plots during 375 discrete events at 63 sites. One of these events was carried on local news outlets as part of Earth Day 2023 celebrations in Miami-Dade County Parks. Additionally, early evidence shows that these beetles are beginning to disperse on their own.
Melaleuca quinquenervia is an Australian tree that once infested about 800 square miles in Florida. Biocontrols developed by IPRL researchers in Fort Lauderdale, Florida have transformed this plant so that it no longer dominates the landscape and is now much easier to control using conventional methods. Releases of the most recent agent, L. indentata, was initiated in June 2023 through the Comprehensive Everglades Restoration Plan (CERP). Mass rearing and releases are being conducted within the CERP footprint along with research to gauge establishment and impact including food web studies, ecological impact studies, field host specificity studies and niche studies to look at the in situ interaction between L. indentata and L. trifida, an established congener.
Old World climbing fern, Lygodium microphyllum, smothers tree islands, cypress domes, pine woodlands, and tropical hammocks in the Everglades and peninsular Florida. Its native range is the Old World tropics. To date, the IPRL has developed and established a moth and a mite whose ranges continue to increase across Florida. In FY 2023, we released over 400,000 brown Lygodium moths (Neomusotima conspurcatalis) and over 10 million Lygodium mites (Floracarus perrepae). We focused these releases on areas within the CERP footprint and the lands managed by Southwest Florida Water Management District, who is an important stakeholder. IPRL scientists continue to optimize F. perrepae rearing and release methods, and increase establishment of the mite, which can cause a fourfold reduction in growth rates of attacked rachises. Through collaborative work with partners at the Australian Biological Control Laboratory, we identified two separate genotypes with low admixtures in the Florida populations. This information, derived from nuclear DNA (RAD Seq) will enable us to better target new areas for herbivore surveys. New biological control agents for lygodium continue to be developed including two leaf feeding moths, a sawfly, and four species of stem borers. We plan to petition for the release of two of these agents: Lygomusotima stria and Callopistria exotica. Both species show a high level of host-specificity in no-choice quarantine tests. We are currently focused on determining environmental limits for survival and reproduction.
Waterhyacinth, Pontederia crassipes, often described as the world’s worst weed, damages ecosystems, economies, and even public health of developing countries. We are currently engaged in an areawide research project to determine optimal strategies for integrating biological control into large-scale weed management for waterhyacinth. This research is focused on field sites on Lake Okeechobee. Our work in the community mesocosms confirmed previous work that the inclusion of herbivores with a chemical control strategy increases the efficacy and longevity of herbicidal control. The mesocosm experiment also elucidated impacts on herbivores (fish), which experience high mortality under waterhyacinth invasions. Once waterhyacinth is under any control (biological control alone, herbicide alone, or a combination), fish populations rebound quickly. Collaborators in Argentina at Fundación para el Estudio de Especies Invasivas (FuEDEI) continue to investigate the feasibility of an additional agent, Thrypticus truncates.
Waterlettuce, Pistia stratiotes, is a floating weed of the southeastern U.S. Genetic research comparing worldwide populations of this weed have identified at least seven distinct clades, three of which may possibly be new cryptic species. One of these appears to be native in countries bordering the Caribbean (including Florida), and another may be more broadly native throughout the Americas (including portions of US Gulf Coast). Initial results from an integrative management experiment indicates that biomass loss is amplified when waterlettuce is treated with both herbicide and biological control. Interestingly, the bulk of the control observed was from native Spodoptera moths.
Azolla pinnata, or feathered water fern, is increasingly problematic in south Florida freshwater ecosystems. Though it is the target of early detection and rapid response efforts, it continues to spread and nascent populations are rising. We began foreign host surveys in 2020 for specialist herbivores in Australia where A. pinnata is native and co-occurs with A. rubra (native) and A. filliculoides (invasive). To date, Dysmicoccus sp., a mealy bug, has been tested and abandoned due to low impact. Elophila sp. defoliating moths were also discovered and initial tests show them to be host specific and high-impact. Bagous clarenciensis were also found on populations of A. pinnata and A. rubra. These populations were tested on no-choice and choice tests in reciprocal crosses and found to maintain affinity for the initial host, indicating that we may be observing a cryptic species complex. More work is being done to ellucidate these potential differences. Finally, we started a small study to look at the possibility of utilizing the native Azolla weevil, Stenopelmus rufinasus, using augmentative releases.
Earleaf acacia (Acacia auriculiformis) is a fast-growing, evergreen tree that invades agricultural, disturbed, and natural areas of Florida in the wetland/upland ecotone. Extensive field surveys in Australia discovered dozens of potential agents two of which are undergoing host range trials. C. intemerata has been tested with 75 species in non-choice tests and shows no signs of the ability to eat or develop on non-target species. We are also nearly completed with temperature development studies; results suggest that neither genotype of this beetle is particularly heat tolerant (reduced development >35 degrees C). We received a shipment of Trichilogaster galling wasps from the colony in Fort Pierce and were able to successfully establish them in our quarantine and begin host-range testing.
A thrips, Pseudophilothrips ichini, is being released for biological control of Brazilian peppertree, Schinus terebinthifolia, an invasive weed of natural and agricultural areas of California, Florida, Hawaii, and Texas (USA). The thrips larvae and adults feed on flushed leaves and stems that are produced during the vegetative season of the host. However, during the reproductive season from September to December in Florida, few flushing leaves are available as resources are shunted to plant reproduction. As field releases were being implemented, thrips were found feeding and damaging immature fruits and flowers of their host. We hypothesized the thrips used volatile organic compounds produced by reproductive tissues to locate and feed on these tissues. In laboratory studied, thrips adults or larvae chose flushing leaves over all reproductive tissues: female flowers, male flowers, and immature fruit. However, to simulate seasons when few flushing leaves were available, additional choice tests were conducted where flushing leaves were omitted, and only reproductive tissues and a blank control were included. Thrips adults or larvae selected all reproductive tissues over blank controls. When presented with a choice between immature and mature fruit, thrips adults or larvae chose immature fruit. Thrips caused significant damage to live female flowers, male flowers, and immature fruit, and thrips survival rates were similar when fed flush leaves, female flowers, or male flowers. The thrips responses could be tied to volatile organic compound production, which significantly varied among tissue types. Volatile blends from flush leaves that include DMNT, Terpinolene, and d-Elemene may attract P. ichini whereas those that repel them include a-Thujene, a-Pinene, ß-Pinene, Camphene, and ß-Phellandrene. These results suggest that P. ichini has a flexible feeding strategy and exploits Brazilian peppertree reproductive tissues when few flushing tips were available. Further they suggest that thrips feeding will have direct impacts on Brazilian peppertree reproduction.
Accomplishments
1. Cogongrass invades many subtropical and tropical areas and is estimated to infest over 500 million hectares world-wide. Asia is most likely the native range of cogongrass from where it was accidentally introduced to the US around 1912 in packing material from Japan. Cogongrass was later intentionally introduced for forage in Texas, Mississippi, Alabama, and Florida. Cogongrass is included in the federal noxious weed list and primarily invades the Gulf Coast states from Texas to Florida, Georgia, South Carolina, and Virginia. With climate change, this weed also has the potential to spread north to Oklahoma and Tennessee, and east to coastal North Carolina. Over 100,000 hectares are infested in Florida, Alabama, and Mississippi where cost of control may approach $ 400 per hectare. Cogongrass produces extensive rhizomes and seeds which allow it to spread, persist, and dominate invaded sites. The weed may reproduce vegetatively from rhizomes and is a prolific seed producer which allows wind dispersed invasion of new areas. Cogongrass leaves can grow to 1.2 to 1.5 meters in height and the plant can thrive in fire-based ecosystems. Although the weed was once thought to be suitable as food for cattle, the low nitrogen content, poor digestibility, and high silicate levels in the leaves deter grazing. Native range surveys for Cogongrass potential agents were conducted in Australia, Japan, and South Africa, and South Korea. Most notable discoveries, these surveys revealed as many as 60 potential new agents, including the crown borer Emmalocera latilimbella (Lepidoptera: Pyralidae), the stem borer Phycitinae sp. (Lepidoptera: Pyralidae), the shoot tip feeder Chloropidae sp. (Diptera: Chloropidae), and the shott borer Atherigona sp. (Diptera: Muscidae). Research to colonize and host range determination will continue.
2. Old World climbing fern, Lygodium microphyllum is one of the worst environmental weeds of southern Florida. The weed climbs over other plants, forming thick mats on shrubs and trees that block sunlight to native plants. In the invaded range, Old World climbing fern invades much of the southern peninsula of Florida where cost-effective, sustainable control methods are needed. A series of no-choice tests on 68 plant species from 45 genera, 33 plant families, and 18 orders indicated that Callopistria exotica is highly specific. Larvae fed and matured to the adult stage on the target weed L. microphyllum (0.71 ± 0.02 proportion survived) and on another invasive fern, L. japonicum (0.84 ± 0.04 proportion survived). An extremely low proportion of larvae survived to the adult stage when fed the non-targets L. palmatum (0.07 ± 0.03), L. venustum (0.01 ± 0.01), and L. volubile (0.07 ± 0.03). All neonates perished within 3 days when fed the remaining 62 species evaluated in these no-choice tests. Climate modeling indicated that the suitability of North American climates for the establishment of C. exotica are very high in south Florida but very unsuitable north of the L. microphyllum invaded range. These results indicated that, this potential biological control agent, is highly specific to L. microphyllum and L. japonicum and will have no, or very low survival on other non-target species. The release of C. exotica will assist in the effort to manage the invasive weed Old World climbing fern.
Review Publications
Madeira, P.T., Diaz, R., Dray Jr, F.A., Rayamajhi, M.B., Lake, E.C., Smith, M. 2023. Population genetic comparison of Lilioceris cheni (Coleoptera: Chrysomelidae) colonies released onto Dioscorea bulbifera in Southeastern USA. Biocontrol Science and Technology. https://www.tandfonline.com/action/showCitFormats?doi=10.1080/09583157.2023.2196016.
Wheeler, G.S., Minteer, C., Rohrig, E., Steininger, S., Halbritter, D.A., Leidi, J.G., Rayamajhi, M.B., Le Falchier, E. 2022. Release and persistance of the Brazilian peppertree biological control agent Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) in Florida. Florida Entomologist. 105(3):225-230. https://doi.org/10.1653/024.105.0308.
Wheeler, G.S., Palacios, J.N., David, A., Read, Q.D., Nestle, R.L. 2023. The Brazilian peppertree biological control agent Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) displays a flexible feeding strategy between foliage and reproductive tissues. Biological Control. 179. Article 105159. https://doi.org/10.1016/j.biocontrol.2023.105159.
Foley Iv, J.R., Williams, J., Pokorny, E.N., Tipping, P.W. 2023. Herbivore suppression of waterlettuce in Florida, USA. Biological Control. 179. Article 105149. https://doi.org/10.1016/j.biocontrol.2023.105149.
