Basics on Aquatic Biological Control

Rodrigo Diaz

Department of Entomology, LSU AgCenter

Aquatic Weed Control-Short CourseCoral Springs, Florida, May 2-5, 2016

Goal: Explain how biological control works and how it has been used for aquatic weed management

1. What is biological control?

2. What steps are involved in biological control

program?

3. How we select biological control agents?

4. Who regulates biological control in United States?

5. What is the history and safety of biological control?

6. Examples of aquatic weed biological control

What is Biological Control?

• Classical biological control-Intentional introduction of agents from the weed’s native range to reduce populations in the introduced range. Agents are released with the expectation of establishment and spread to achieve long-term control

• Biological control agents are host-specific insect herbivores, mites or plant pathogens that have co-existed with their host plant (target weed)

Biological control agents are monophagous

Types of host specificity:

• Monophagous: feeding on one plant species or one

genus

• Oligophagous: feeding on species in the same family

• Polyphagous: feeding on species of different families

Price et al. 2011

Native range Introduced range

Enemy Release Hypothesis (ERH)

Biological control

Evolution of increase competitive ability (EICA)

Native range

In the absence of natural enemies, plant reallocate resources from defense to growth and reproduction increasing its competitive ability

Introduced range

Blossey and Notzold 1995

What is the ideal case in a biological control program?

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25

Abun

danc

e

Time

Weed

Equilibrium

v v v

Agent

How we can measure the success of a biological control program?

Hoffmann’s definitions:1. Complete: no other control method is required

2. Substantial: other methods are needed but reduced efforts

3. Negligible: control dependent on other control measures

Different levels of success (Delfosse 2004):

1. Biological: measure of management of the target weed 2. Ecological: sustainable, low-input, and energy-conserving management3. Economical: calculate benefit-cost ratios4. Social: individuals across society5. Legal: laws and regulations that facilitates biological control6. Scientific: Knowledge gain of ecological systems under study7. Political: long-term and increasing support for biological control

Weed biological control programs:

60% agents established50% resulted in some level of control

Economic benefits: cost ratios range from 7:1 to 36:1

1. Theory and definitions

2. Steps in biological control of weeds

Steps during a biological control of program

‘Pipeline’

5. Technologytransfer

4. Field releases/ Establishment

3. Quarantine(host range tests)

2. Surveys/Researchin native range

1. Select target weed

5 to 10 years to complete

1. Select target weed

• Which other methods of control are available?

• Cost-benefit analysis of using biological control

• Has this weed been a target for biological control

elsewhere?

• Are there any conflict of interests?

• Species identification and area of origin of the

target weed

2. Surveys and research in the native range

• Foreign explorations in the weed’s native

range

• Surveys and collections of natural enemies

• Studies on the ecology of the weed and

natural enemies in the native range

• Field host range of potential agents

3. Quarantine

• Import insects to quarantine using

appropriate permits and labels

• Establish insect colonies in quarantine

• Studies on biology and impact of

potential agents

• Conduct host range testing

(specificity!)

4. Field releases and establishment

• Mass rearing of biological control agents

• Select field sites and method for releases

• Initiate field releases, monitor establishment and spread

• Evaluate impact of agents in the field:1. Before and after

2. Exclusion using cages or insecticides

3. Long-term studies evaluating reduction of weed populations

5. Technology transfer

Extension agentsScientists Cattle ranchers

• Tropical soda apple (Solanumviarum) weed of pastures in FL

• Leaf beetle Gratiana bolivianareleased in 2003

5. Technology transfer

1. Theory and definitions

2. Steps in biological control of weeds

3. Selection of biological control agents (host specificity!)

Things to consider during agent selection

• Host specificity and risks to non-target species

• Adaptation to plant genotypes (DNA studies)

• Climate match between origin and introduced range

(e.g. CLIMEX)

• Impact to target weed (e.g. reduced growth and

reproduction)

• How many biological control agents should be released

Host range testing: Centrifugal PhylogeneticMethod

Target weed

Other subgenus, same genus

Other genus, same tribe

Other tribe, same family

Plants of economic importance

Test plant list: close related nativespecies, economic importance, and threatened or endangered

species

Other species, same subgenus

Host range testing – critical step

1. No-choice tests: larval development / adult oviposition

YES

2. Multiple-choice tests: agent preference

YES

3. Open field tests

Risks to non-targets – Direct effects

• Plants that are close related to the target weed have higher risks of non-target effects (similar chemistry, etc.)

• Example: The weevil Rhinocyllus conicus released against exotic Carduus thistles in the US in 1969. BUT the weevil attacked native Circium thistles in 1980s

• Plants from the same tribe: Cynareae

• Feeding on native thistles was consistent with host specificity testing

• But there was a lack of concern over non-economic native species

http://www.forestryimages.org

Risks to non-targets – Unintended effects

• Cactoblastis cactorum was released in Caribbean (Nevis) in 1957 and was first reported in Key West, FL in 1989

Pear prickly cacti in FL

http://www.floridainvasives.org/Heartland/links/CactoblastusMothHeatherJezorekUSF.pdf

Risks to non-targets – Indirect effects

• Leaf feeding beetle Diorhabda carinulata (= D. elongate) released in 1999 against saltcedar (tamarix spp.) in Nevada and Utah

http://fcwp.org/BioControl/Saltcedar.html

Endangered bird the southwestern willow flycatcher used saltcedar for nesting in western riparian ecosystems

http://www.fws.gov/utahfieldoffice/swfl.html

DeLoach et al. 2004, Dudley and Bean 2012

Host-plant genotypes

• Brazilian peppertree Schinus terebinthifolia is an invasive species in FL. Genetic studies determined that two haplotypes (A, B) has been introduced in Florida.

A

ML

B-K

Native Range: Brazil

AC-D

A

West coast (A)

East coast (B)

Hybrids A, B

Introduced range: Florida

Pseudophilothrips gandolfoi: poor performance on FL types

Pseudophilothrips ichini: good performance on FL types

Williams et al. 2005, 2007; Manrique et al.

Climate match

• Successful biological control of water hyacinth (Eichhornia crassipes) in East Africa, Argentina, Australia, USA, India, Thailand (tropical or subtropical areas).

• But this did not occurred in South Africa. Worst infestations found in the Highveld: high-altitude, extreme winter temperatures

Julien et al. 2000

Insect densities remained low or failed to persist in the Highveld. In addition, eutrophic waters with high nutrient levels allow plants to recover

http://www.bonniesplants.com/floating_plants/water_hyacinths

Neochetina eichhorniae

Water hyacinth

Single vs. multiple biological control agents

• Lottery model: multiple agents are released to increase likelihood of success

• Silver bullet: a single agent capable of reducing pest populations

• Cumulative stress hypothesis: multiple agents are released to exert

sufficient damage to the target weed

Harris 1981, Myers 1985

1. Theory and definitions

2. Steps in biological control of weeds

3. Selection of biological control agents

4. Regulations and permitting process in USA

Petition for field releases

TAG Committee: Technical Advisory Group (1987)• Independent assessment of the safety

of biological control agents.• Composed by 15 governmental

agencies from USA, Canada, and Mexico.

Coombs et al. 2004

Format of Petition• Target weed information

• Biological control agent information

• Experimental methodology and analysis

• Results and discussion (host range tests)

• Protocol for releasing the agent

• Post-release monitoring

• Benefit/Risk

• Potential Environmental Impacts

• Petitioner’s Conclusion

1. Theory and definitions

2. Steps in biological control of weeds

3. Selection of biological control agents

4. Regulations and permitting process in the USA

5. History and safety of weed biological control

History – Early successes

First successful biological control program of weeds (Australia)

http://en.wikipedia.org/wiki/Cactoblastis_cactorum

Cactoblastis cactorum from Argentina was introduced against prickly pear species (Opuntia spp.) in Australia

Julien and Griffiths 1998

History – Early Successes

• 1930s: First successful biological control of weeds in USA

• Leaf beetle Crysolina quadrigemina against St John’s wort (Hypericum perforatum) in California

Julien and Griffiths 1998

http://www.parfaitimage.com/Insecta/chrysolina_quadrigemina.html

History – Lessons learned during the last 100 years

• Improved protocols of host range testing

• Close relatives have higher risks of non-target effects

• Importance of selecting effective agents

• Risk-benefit-cost analysis

• Long-term post-release evaluations of biocontrol

programs

Safety of biological control of weeds

• Precautionary Principle (1992)

• International code of best practices for Classical biological control of weeds (Balciunas 2000)

• Independent TAG committee (1987)

• Government Regulations/Permitting by USDA-APHIS-PPQ

• Outstanding record of safety: 133 weed species targeted, >350 biological control agents introduced, only 8 agents damaging non-target spp. but none at population levels

Julien and Griffiths 1998, Waterhouse 1999

Summary of how biological control works

• Classical Biological Control is the intentional release of

host-specific natural enemies to reduce weed populations

• Host specificity testing is critical during agent selection

• Climate match, genotype adaptations, and impact on the target weed

• USDA-APHIS-PPQ regulates biological control introduction

• Risk-benefit-cost analysis should be central for the release of agent

• Weed biological control has a long history of safety and success

Examples of classical biological control of aquatic weeds

What factors might influence the success of biological control program in aquatic systems?

Connectivity Plant quality: Fertilizer

Hydroperiod Use or disturbance

Alligatorweed (Alternanthera philoxeroides) Amaranthaceae

Native range: Eastern coast of South America

Heavy infestations disrupt water flow and large mats can float against bridges and dams. Hinders boat traffic and fishing.

Exotic range: SE USA including Florida, Alabama, Georgia, Louisiana

Alligatorweed flea beetle (Agasicles hygrophila) Coleoptera: Chrysomelidae

Native range: South America

Destructive stages: Larval and adult

Site of attack: Primarily leaves, stems

Impact: Massive defoliation during heavy attack, leading to submergence of floating mat

Successful control by the flea beetle in Florida stimulated programs on water hyacinth and other aquatic weeds

Hydrilla (Hydrilla verticillata)Hydrocharitaceae

Native range: Africa, Australia, Asia

Invades all types of water bodies, tolerant of acidic, highly calcareous and brackish water.

Cold climate does not seem to be a limiting factor.

Exotic range: SE USA Currently spreading north.

Indian hydrilla leaf-mining fly (Hydrellia pakistanae)Diptera: Ephydridae

Native range: Pakistan to China

Destructive stages: Larval

Site of attack: Leaves

Impact: Leaves with mines decay and at heavy infestations stems become necrotic

First introduced in the United States: 1987, in Florida. Established in: Alabama, Arkansas, Florida, Georgia, Louisiana, Texas.

Reduces photosynthetic ability and tuber numbers, eventually causing the plant to sink

Giant salvinia (Salvinia molesta)Salviniaceae

Native range: Southeastern Brazil

Exotic range: Louisiana, Texas with some minor infestations in south eastern USA

Forms thick mats. Blocks drains, irrigation systems, carries insects such as mosquitoes, reduces oxygen, displaces native plants.

Salvinia weevil (Cyrtobagous salviniae)Coleoptera: Curculionidae

Native range: South America

Destructive stages: Larval and to lesser extent adult.

Site of attack: Buds and rhizomes.

Impact: Plants turn brown, eventually sink

First introduced into the US in 2001. Successful control in southern Louisiana

Drastic results in several countries, ex. South Louisiana

Eurasian watermilfoil (Myriophyllum spicatum)Haloragaceae

Native range: Africa and Eurasia

Natural lakes, rivers, brackish coastal waters. No apparent climate limit except USDA Zone 1 and 2 in north and 10 and 11 in south.

Exotic range: 37 states including Alaska and Florida

Watermilfoil moth (Acentria ephemerella)Lepidoptera: Pyralidae

Native range: Europe

Destructive stages: Larval

Site of attack: Stems and leaves

Impact: Girdles leaves and stems during feeding, leaves and stems drop off plant

Larvae feed on a variety of non-target plant species but does not cause similar damage to non-target plants in field studies

Established in Iowa, Massachusetts, Michigan, Minnesota, New Hampshire, New York, Vermont and Wisconsin.

West Indian marsh grass (Hymenachne amplexicaulis), Poaceae

Native range: South America and the West Indies

Invades wetland marshes and flood plains, drastic changes in hydroperiod, large biomass accumulation

Exotic range: Florida

Myakka bug (Ischnodemus variegatus)Hemiptera: Blissidae

Native range: South America

Destructive stages: nymphs, adults

Site of attack: sap feeder

Impact: At heavy infestations causes leaf damage and stunted growth

Smooth cordgrass (Spartina alterniflora)Poaceae

Native range: Atlantic and Gulf coasts of North America

Exotic range: California and Washington

Changes vegetation type of infected areas, displaces native plants and animals

Delphacid bug (Prokelisia marginata)Hemiptera: Delphacidae

Native range: Atlantic and gulf coasts of North America.

Destructive stages: Nymph and adult

Site of attack: Leaves, sap-feeder

Impact: reduction in biomass, mortality

Cage studies conducted in Willapa Bay, Washington

Waterhyacinth (Eichhornia crassipes)Pontederiaceae

Native range: Tropical South America

Exotic range: California, Florida, Hawaii, Louisiana, Texas, Puerto Rico

Creates mats, changes vegetation type, prevents navigation, clogs pumps, intensify mosquito problems, reduces oxygen and photosynthesis for native plants

Waterhyacinth weevils (Neochetina spp.)Coleoptera: Curculionidae

Native range: South America

Destructive stages: Larvae, adults

Site of attack: Leaves and lateral buds

Impact: Reduces photosynthetic area, causes desiccation, might sink mats

Waterlettuce (Pistia stratiotes)Araceae

Native range: Africa, Asia and South America

Exotic range: Subtropical Florida, Gulf Coast states, California

Forms mats, depletes oxygen, causes thermal stratification, increases mosquito problems.

Waterlettuce weevil (Neohydronomus affinis)Coleoptera: Curculionidae

Native range: South America

Destructive stages: Larval and adult

Site of attack: Leaves and shoots.

Impact: Stressed plants due to weevil damage are smaller and have fewer leaves, destruction of buoyancy

Summary on aquatic weed biological control

- Biological control could help on reducing the inputs of herbicides into the watersheds.

- Watershed connectivity, water-plant quality (fertilizer, pesticides), hydroperiod and disturbance might affect the outcome of the program.

- Programs developed for emergent, floating and submersed aquatic weeds.

- Biological control agents have remarkable adaptations to the aquatic environment.

- Impacts of agents measured at different scales ranging from reduction leaf damage, defoliation to reduction of biomass.

Thanks for your attention!