Biological control of invasive weeds: the fight against the homogenization and decline of the earth s floral biodiversity

Transcription

1 Biological control of invasive weeds: the fight against the homogenization and decline of the earth s floral biodiversity Bill Overholt Biological Control Research and Containment Laboratory Indian River Research and Education Center University of Florida Aquatic Weed Short Course, May 2012

2 Outline What are invasive plants and why are they a problem? Why do only some exotic plants become invasive? some hypotheses Biological control as an approach for managing invasive plants

3 The breakup of Pangea

4 Species/area relationships Vitousek et al Am. Sci. 84:

5 Adaptive radiation Species 4 Species 5 Species 6 Species 7 Species 2 Species 3 Time Species 1

6 So, what s the issue? Homogenization of the earth s biota Geographic barriers have broken down. Due to increased, and faster travel, exotic species are being moved around the world with unprecedented frequency For example, in Hawaii, the rate of introduction of new insects prior to human colonization (around 400 AD) has been estimated at one species every 50,000 to 100,000 years. Currently, there are new insect species introduced every year (Beardsley, 1979). This is million more introductions per year since human colonization. Beardsley, J. W New immigrant insects in Hawaii: 1962 through Proceedings of the Hawaiian Entomological Society 23:35-44.

7 Exotic plants The vast majority of plant introductions have been deliberate Many of introduced plants are useful, e.g. citrus, sugarcane, corn, soybeans. A few become invasive and harm to agricultural and natural areas

8 What is an invasive plant? An alien plant that spreads naturally in natural of semi-natural habitats and results in change in terms of species composition or ecosystem processes in Florida, there are currently 76 species on the FLEPPC Category I list and an additional 76 species on the Category II list this species represents about 11% of the nearly 1200 alien species that are naturalized in the state

9 Why are we concerned? loss of biodiversity loss of endangered and threatened species and their habitat 42% of species on the US endangered/threatened list are there because of competition with exotic species! Competition with invasive species ranks second only to habitat destruction a cause for decline of native species loss of habitat for native insects, birds, and other wildlife changes to natural ecological processes such as plant community succession

10 The food chain Carnivores (Tertiary consumers) Carnivores Carnivores (Secondary consumers) Herbivores Decomposers (Primary consumers) Plants Sun (Primary producers) (Energy)

11 Origin of invasive plants in Florida Allilgatorweed Air potato Taro Guava Brazilian peppertree Old world climbing fern Unknown Ornamental Agricultural Aquarium trade Forage Packing material Ballast

12 The invasion process Native elsewhere Survival in transport Establish in new area Lag period Spread Ecological impact Human impact adapted from Sakai et al. 2001

13 What can be done? Regulation Prevention Native elsewhere Survival in transport Mechanical control Chemical control Biological control Eradication Management Establish in new area Lag period Spread Ecological impact Human impact

14 Why are invasive plants a problem in areas of invasion but not in their native homes? Some hypotheses: Hybridization Novel weapons Suppression by herbivores and diseases

15 Hybridization hypothesis Basis of hypothesis often an exotic plant is introduced more than once, at times from different geographic areas (this may be particularly true with ornamentals which account for ~ 70% of invasive plants in Florida) once two or more populations are established, they may hybridize hybridization produces new genetic combinations that may allow rapid evolution and adaptation to a variety of habitats

16 Example: Brazilian peppertree Native to Brazil, Paraguay, Uruguay and northern Argentina Introduced into FL as an ornamental in 1800s Invades a variety of habitats including disturbed areas as well as pinelands, hardwood hammocks and mangrove forests

17 1832: Advertised in a NY seed catalog : Specimen collected in Florida by Ferdinand Rugel 1898: Introduction of seeds from France and Algeria into USDA Plant Introduction Center in Miami Introduction history 1900: Introduction from somewhere in Brazil into west coast Florida.

18 Invasion of natural habitats

19 Molecular evidence of introduction history Chloroplast Nucleus Chloroplast DNA Nuclear DNA + A x B + AA x BB A AB

20 Results chloroplast DNA A A B B Williams et al Mol. Ecol. 14:

21 Origin of Florida BP types B A Williams et al Heredity 98:

22 Nuclear DNA Percent eastern ancestry Percent western ancestry Williams et al Mol. Ecol. 14:

23 Climate modeling A B Mukherjee et al Biological Invasions DOI /s

24 What would happen if additional types of Brazilian peppertree were introduced?

25 Hybrid advantage? Total fitness = seed weight x % germination x seedling survival x seedling dry weight Geiger et al Int. J. Plant Sci. 172:

26 Summary Two types of Brazilian pepper were introduced into Florida They have hybridized extensively since introduction The origins of the two types have been identified in Brazil The climates at the source populations only match restricted areas in south Florida, suggesting that the two types could gain a foothold in the state. Hybridization may have allowed the northward expansion in Florida

27 Novel weapons hypothesis Exotics may produce chemicals (allelochemics) that decrease the competitive ability of natives. Plants in the exotic s home may not be as susceptible to these chemicals because they have evolved defense mechanisms. Example: Diffuse knapweed, an invasive species in the western USA. Diffuse knapweed produces chemicals that negatively effect native vegetation in the USA. Related plants from Eurasia (knapweed s native home) are tolerant of these chemicals (Callaway and Aschehoug, 2000).

28 Native range Introduced range

29 Brazilian Peppertree: allelopathy Purpose: To investigate allelopathic effects of BP on native plants and vice versa. Test the novel weapons hypothesis Methods: Irrigate plants with root exudates Irrigate plants with aqueous leaf extracts

30 Effect of Schinus leaf extracts on germination Bidens alba % Germination Day after planting Water Schinus Oak

31 Rivina humilis % Germination Control Schinus Day after planting

32 Effect of BP leaf extracts on growth Bidens alba Rivina humilis % Germination a b a Weitht (g) a b Control Schinus Quercus Treatment 0 Control Treatment Schinus

33 Conclusions Brazilian pepper negatively affects at least some native plants This may be a factor in the invasiveness of Brazilian pepper

34 Biological control the use of natural enemies to reduce the damage caused by a weed population Types of biological control Classical (= introduction) Augmentation Conservation

35 Classical biological control of weeds Based on the natural enemy hypothesis Exotic plants escape their natural biotic regulating factors (herbivores and diseases) when they are moved from one area of the world to another. Escape from their natural enemies allows the exotic plant to reach higher densities in the invaded range than in the native range. Classical biological control is the practice of reuniting exotic invasive species with their coevolved natural enemies

36 How Biological Control Works Native home Invaded area Biological Control

37 Advantages of classical biological control Permanent solution when it works Low cost Safe

38 Costs / Benefits of Classical Weed Biocontrol Programs Release of Bioagent Benefits (+$) Time Costs (-$) Research & Development Maintenance & Monitoring (after Mentz 1987)

39 Steps in classical biological control of plants Taxonomic identification of the invasive plant Identification of the native range Foreign exploration for natural enemies Host specificity tests in country of origin Selection of agents thought to be host specific Introduction through quarantine

40 Steps in biocontrol (con t) Host specificity testing under quarantine conditions (related native plants and economically important plants) Petition for permission to release Release Evaluation of establishment, spread and impact

41 Approach: The pipeline

42 Most important characteristic of biological control agents Host specificity!!

43 Host range testing: Centrifugal Phylogenetic Method Target Weed Economic, Native and Endangered spp. Other Plant Species; same subgenus Other Subgenera; same genus Other Genera; same tribe Plant Families of Economic/Aesthetic Value Plants Attacked by Relatives of Bioagents Redrawn from Rees et al., 1995

44 Screening Sequence (Wapshere 1989) TEST 1 Feeding Test + - No-Choice: Close Confinement NOT IN HOST RANGE TEST 2 TEST 3 Adult Oviposition Test #1 + - Adult Oviposition Test #2 + - IN HOST RANGE No-Choice: Close Confinement NOT IN HOST RANGE Multiple Choice: Loose Confinement NOT IN HOST RANGE

45 Aquatic weed biocontrol in Florida: Alligatorweed the first attempt Origin: Venezuela, Argentina First reported in the US in the 1890s Caused severe problems in waterways in the southern US in the early 1960s - 66,723 acres of waterways infested in 8 states in 1963

46 Biological control agents Alligatorweed thrips (Amynothrips andersoni) Released in 1967 Established, but doesn t appear to do much

47 Agents (con t) Alligatorweed stem moth (Arcola malloi) First released in 1971 Established throughout Florida, but little impact In the lower Mississippi River area, it is credited with providing good control

48 The big success Alligatorweed flea beetle (Agasicles hygrophila) First release in 1965 Excellent control in Florida By 1971, alligator weed was under good control

49 Hydrilla Native to Asia, Australia and eastern Africa Introduced into Florida as an aquarium plant Dumped into a canal near Tampa in the 1950s Can grow to 15m in length Currently the most serious invasive aquatic plant in the state

50 Introduced biological control agents Weevils Bagous affinis Pakistan released in 1987 tuber borer not established Bagous hyrillae Australia released in 1991 stem borer not established

51 Flies Hydrellia balciunasi Australia released in 1989 leaf miner recovered from a few sites in Texas Hydrellia pakistanae - Pakistan released in 1987 leaf minor established, found throughout Florida some control reported in Georgia and Texas

52 Exotic species not intentionally released Cricotopus lebetis Found in 1992 in Crystal River Studied by Cuda Larvae feed in apical meristems Unknown origin Appeared to provide some control in Crystal River Not host specific Parapoynx diminutalis Moth Asian origin In Florida, but not very effective

53 Augmentative biological control with grass carp Origin: Asia Sterile triploid developed in 1990s Stocking rate: /acre Live for ~ 10 years

54 Water hyacinth Introduced from South America in to the US in 1884, arrived in Florida in 1890 The infestation in Florida was estimated at 200,000 acres in 1972

55 Biological control Two beetles released Neochetina eichhorniae Neochetina bruchi 1974 One moth Niphograpta albiguttalis

56 Success? Depends on your point of view Biocontrol agents in managed and unmanaged hydrilla Center et al Environemental Management 23:

57 Water lettuce Origin of weed uncertain Found in Florida in 1765 may have been introduced in ship s ballast The weevil Neohydronomus affinis released in 1987 Reportedly weakens plants but herbicides still required

58 Melaleuca Introduced into Florida in the late 19 th century as an ornamental and to dry up marshes Currently infests more than 500,000 acres Three biological control agents released A weevil A psyllid A gall midge

59 Impact of Melaleuca biocontrol Melaleuca density Plant diversity Rayamaji et al Wetlands Ecology and Management

60 Tropical Soda Apple (Solanum viarum) Perennial weed from South America At maturity, ca. 1m in height Produces 40,000-50,000 seed per plant Cattle eat the fruits, but not the prickly foliage, thereby spreading the plant to new locations First reported in Florida in 1988 in Glades Co. Estimated to infest 1 million acres in of pastures/rangeland in Florida??? Losses estimated at $6-16 million/year, primarily in costs of herbicides and lower cattle stocking rates 1 inch

61 Biological control of tropical soda apple The beetle, Gratiana boliviana was introduced from Paraguay Host range testing on 118 plants revealed that G. boliviana would only feed and reproduce on tropical soda apple G. boliviana first released in Florida in 2003

62 Gratiana releases Released at ~ 400 locations 200,000 beetles released

63 Gratiana density in Florida, fall 2008

64 Plant performance at sites with or without G. bolviana damage 120 B cm or number A B A GB No GB B 20 A 0 Height Diameter Fruit

65 Modine ranch Saint Lucie Co. Number of plants Plant density meanplts meangb Beetles Number of plants with fruit Date Fruit production meanfrt meangb Date Beetles

66 July 2006 October 2007

67 Summary Invasive plants negatively affect biodiversity and may alter ecological processes There are several reasons why some plants may become invasive, including: hybridization, novel weapons lack of natural enemies Biological control may be useful for mitigation of invasive plant problems Host specificity is the most important attribute of a biological control agent

68 QUESTIONS?