Background on Biological Control and Giant Salvinia

Rodrigo Diaz LSU AgCenter

Outline

• Background on Biological Control • Definition • Steps • Importance of safety

• Biological Control of Giant Salvinia • Background on salvinia and weevil • How to do releases of weevils • Importance of monitoring impact and wetland recovery

Biological control is a safer management tool in aquatic ecosystems

Using host specific insects, we might reduce the input of chemicals to the watershed

Flora and fauna Human consumption

What is Biological Control?

The use of populations of natural enemies to suppress pest populations to lower densities, either permanently or temporarily.

Neochetina eichhorniae Water hyacinth

One explanation for population increase of non-native species is the escape of natural enemies

Native range Introduced range

Biological control

Steps during a biological control program

‘Pipeline’

5. Technology transfer

4. Field releases/ Establishment

3. Quarantine (host range tests)

2. Surveys/ Research in native range

1. Select target weed

5 to 10 years to complete

Host range testing: Centrifugal Phylogenetic Method (Wapshere, 1974)

Target weed

Other species in same family

Other tribes, same family

Other families

Plants of economic importance

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

species

Other species in the same genus

Climate match between donor and recipient country is critical

• Successful biological control of water hyacinth (Eichhornia crassipes) in East Africa, 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

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

Connectivity Plant quality: Fertilizer

Hydroperiod Use or disturbance

Natural enemies have remarkable adaptations for aquatic environments

Hydrilla fly Watermilfoil moth

Smooth cordgrass bug Water lettuce weevil

Measure agent impact in the field

• Before and after

• Exclusion using cages

or insecticides

• Long-term studies

evaluating reduction of

weed populations

Important: We need to know how to monitor populations of natural enemies

Biological control of Melaleuca in Florida

• Replicated insect exclusion studies (insecticides):

• 76% reduction in regrowth • 80% mortality of cut stumps

Herbivory Control

Pratt et al. 2008 Reduction of flowering due to weevil damage

Technology transfer allows scientists to communicate with our stakeholders

Field days Non-technical publications

Social Media and YouTube Scientific Publications

FREE: Great reference book about biological control agents for aquatic weeds

https://www.ars.usda.gov/is/np/aquaticweeds/aquaticweeds.pdf

Pictures for identification Plant hosts Biology and ecology Impact on host plant

Not free, but a great source of information about biological control of invasive weeds in USA

Take home messages:

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

- Several components including 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

Biological control of giant salvinia

Giant salvinia (Salvinia molesta) is a fern native from Brazil

Reduction of habitat for game birds

Block canals

Displacement of native vegetation

Limit the access to fishing

Fast population growth

Salvinia weevil has been used for salvinia management in many countries

Can we improve biological control based on needs of stakeholders?

All year November 12th to January 22nd

Is biological control reducing salvinia coverage?

Is there a recovery of local vegetation?

Where we can get weevils? Natural infestations or rearing ponds

Releases: The goal is to facilitate the establishment of weevils

Releases should be made on actively growing salvinia, avoid thick mats

Weevils love new buds: higher N levels favor reproduction

Monitoring is critical to determine condition of plants and weevils

Impact of the weevil in the field

• Large infestations reported in Cameron Parish in April 2016

• Established long term monitoring system in June 2016

Field conditions in June, note browning of salvinia

Monitoring helped to quantify the changes in biomass over the growing season

Salv

inia

bio

mas

s (g)

June July August September

Unit =0.08m2

December

June 2016

August 2016

July 2016

June 2016 July 2016

August 2016 Sept. 2016

June 2016

August 2016

July 2016

Sept. 2016

Lots of weevils per kilo of salvinia early in the growing season

Adul

ts p

er k

ilo

June July August September December

After salvinia sunk, submerged aquatic vegetation showed up increasing dissolved oxygen

Common SAVs: Cabomba (Cabomba), bladderwort (Utricularia), eelgrass (Vallisneria) Others: Frogbit (Limnobium), Water hyacinth (Eichhornia), Alligatorweed (Alternathera)

Earlier crashes led to a faster recovery of submerged vegetation

Success is limited to southern regions. What might be the problem in the north?

N

S

Information: plant and weevil recognition, news, resources, monitoring tools

www.lsuagcenter.com/giantsalvinia

Take home messages:

Thanks for your attention!

Access to weevils: Natural infestations or mass reared

Release method: Know what weevils need for successful establishment

Monitoring: Know the distribution and densities of weevils is critical