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

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

The breakup of Pangea

Species/area relationships

Vitousek et al. 1996. Am. Sci. 84: 468-478

Species 1

Adaptive radiation

Species 2 Species 3

Species 5 Species 6 Species 7 Species 4

Tim

e

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 15-20 new insect species introduced every year (Beardsley, 1979). This is 0.75 – 1.5 million more introductions per year since human colonization.

Beardsley, J. W. 1979. New immigrant insects in Hawaii: 1962 through 1976. Proceedings of the Hawaiian Entomological Society 23:35-44.

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

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

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

Plants

(Primary consumers)

(Secondary consumers)

(Tertiary consumers)

(Primary producers)

Sun (Energy)

The food chain

Herbivores

Carnivores Carnivores

Decomposers

Carnivores

Unknown

Ornamental

Agricultural

Aquarium trade

Forage

Packing material

Ballast

Origin of invasive plants in Florida

Brazilian peppertree Old world climbing fern

Air potato

Taro Guava

Allilgatorw

eed

Native elsewhere

Survival in transport

Establish in new area

Lag period

Spread

Ecological impact

Human impact

The invasion process

adapted from Sakai et al. 2001

Native elsewhere

Survival in transport

Establish in new area

Lag period

Spread

Ecological impact

Human impact

Pre

vent

ion

Era

dica

tion

Man

agem

ent

What can be done?

Regulation

Mechanical control

Chemical control

Biological control

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

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

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

1832: Advertised in a NY seed catalog

1842-49: Specimen collected in Florida by Ferdinand Rugel

1898: Introduction of seeds from France and Algeria into USDA Plant Introduction Center in Miami

1900: Introduction from ‘somewhere in Brazil’ into west coast Florida.

Introduction history

Invasion of natural habitats

Chloroplast

Nucleus

Chloroplast DNA Nuclear DNA

+ A B x

A

+ AA BB x

AB

Molecular evidence of introduction history

Results – chloroplast DNA

A

B A

B

Williams et al. 2005. Mol. Ecol. 14: 3643-3656

A

B

Origin of Florida BP types

Williams et al. 2007. Heredity 98: 284-293

Nuclear DNA

Williams et al. 2005. Mol. Ecol. 14: 3643-3656

Percent eastern ancestry

Percent western ancestry

Climate modeling

Mukherjee et al. 2012. Biological Invasions DOI 10.1007/s10530-011-0168-7

A

B

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

Hybrid advantage?

Total fitness = seed weight x % germination x seedling survival x seedling dry weight

Geiger et al. 2011. Int. J. Plant Sci. 172: 655-663

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

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).

Native range Introduced range

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

Effect of Schinus leaf extracts on germination

0102030405060708090

100

1 2 3 4 5 6 7 8 9 10Day after planting

% G

erm

inat

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WaterSchinusOak

Bidens alba

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ControlSchinus

Rivina humilis

Effect of BP leaf extracts on growth

0

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Control Schinus 0

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Control Schinus Quercus

Bidens alba Rivina humilis

Conclusions

• Brazilian pepper negatively affects at least some native plants

• This may be a factor in the invasiveness of Brazilian pepper

Biological control

• the use of natural enemies to reduce the damage caused by a weed population

• Types of biological control – Classical (= introduction) – Augmentation – Conservation

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 co-evolved natural enemies

How Biological Control Works

Native home Invaded area

Biological

Control

Advantages of classical biological control

• Permanent solution when it works

• Low cost • Safe

Costs / Benefits of Classical Weed Biocontrol Programs

(after Mentz 1987)

Release of Bioagent

Time

Benefits (+$)

Costs (-$)

Research & Development

Maintenance & Monitoring

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

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

Approach: The “pipeline”

Most important characteristic of biological control agents

Host specificity!!

Economic, Native and Endangered spp.

Target Weed

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

Host range testing: Centrifugal Phylogenetic Method

Screening Sequence (Wapshere 1989)

NOT IN HOST RANGE

+ -

NOT IN

HOST RANGE

+ -

IN HOST RANGE

NOT IN HOST RANGE

+ - Feeding Test TEST 1 No-Choice: Close Confinement

Adult Oviposition Test #1 TEST 2 No-Choice: Close Confinement

Adult Oviposition Test #2 TEST 3 Multiple Choice: Loose Confinement

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

Biological control agents

Alligatorweed thrips (Amynothrips andersoni)

• Released in 1967 • Established, but doesn’t appear

to do much

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

The big success – Alligatorweed flea

beetle (Agasicles hygrophila)

– First release in 1965 – Excellent control in

Florida – By 1971, alligator

weed was under good control

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

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

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

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

Augmentative biological control with grass carp

• Origin: Asia • Sterile triploid developed in 1990s • Stocking rate: 20-255/acre • Live for ~ 10 years

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

Biological control

• Two beetles released – Neochetina eichhorniae - 1972 – Neochetina bruchi – 1974

• One moth – Niphograpta albiguttalis - 1977

Success? Depends on your point of view

Center et al. 1999. Environemental Management 23: 241-256

Biocontrol agents in managed and unmanaged hydrilla

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

Melaleuca – Introduced into Florida in

the late 19th century as an ornamental and to dry up marshes

– Currently infests more than 500,000 acres

– Three biological control agents released

• A weevil - 1997 • A psyllid - 2002 • A gall midge - 2005

Impact of Melaleuca biocontrol Melaleuca density Plant diversity

Rayamaji et al. 2009. Wetlands Ecology and Management

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

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

Gratiana releases 2003-2011

• Released at ~ 400 locations

• 200,000 beetles released

Gratiana density in Florida, fall 2008

0

20

40

60

80

100

120

Height Diameter Fruit

cm o

r num

ber

GB No GB

A

Plant performance at sites with or without G. bolviana damage

B

B

A B

A

Modine ranch – Saint Lucie Co.

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meangb

July 2006

October 2007

• 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

Summary

QUESTIONS ?