Prospects for biocontrol of aquatic weeds in New Zealand

1
Prospects for biocontrol of aquatic weeds in New
Zealand
Quentin Paynter Paul Champion
2
History

• In the past it was assumed that classical
  biocontrol of aquatic weeds was unlikely to
  succeed e.g.
• It may be that the relatively small numbers of
  species of plants phytophagous insects,
  perhaps the domination of this environment by
  fish, have caused in aquatic phytophagous insects
  a level of host specialization much lower than
  occurs in the species-rich terrestrial
  environment1
• Aquatic ecologists have noted that the diversity
  of the ingested food greatly exceeds the
  diversity of the aquatic insects the majority of
  species appear to be generalists (polyphagous)
  rather than specialists (mono-or oligophagous)2

1Wilson F 1964 The biological control of weeds.
Annual Review of Entomology, 9,
225-244. 2Cummins KW 1973 Trophic relations of
aquatic insects. Annual Review of Entomology, 18,
183-206.
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History

• Since then a number of aquatic weeds have been
  targeted for biocontrol, with significant to
  spectacular impacts e.g. virtual 100 reduction
  of Salvinia molesta in Australia, South Africa
  USA

Lake Moondarra, Mt Isa, Queensland (Left
before Right after release of the weevil
Cyrtobagous salviniae) Photos CSIRO
Room, P. M., et al. 1981 Successful biological
control of the floating weed salvinia. Nature,
294, 78-80.
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History

• Eichhornia crassipes Control by Neochetina spp.
  often excellent where the weed is not subjected
  to regular removal by periodic or annual flows,
  or mechanical herbicide treatments1

• e.g. Kisumu Yacht Club Lake Victoria, Kenya June
  December 1999, before after biocontrol
  (Photos CSIRO)

1Gassmann, A. et al. 2006 The potential for
biological control of invasive alien aquatic
weeds in Europe a review. Macrophytes in Aquatic
Ecosystems From Biology to Management (ed K.
Martens), pp. 217-222. Springer Netherlands.
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Hydrilla verticillata in the USA
Hydrellia flies reduced Hydrilla biomass by
66
Grodowitz, M. J., et al. (2004) Hydrellia
pakistanae and H. balciunasi, insect biological
control agents of hydrilla boon or bust?
Proceedings of the XI International Symposium on
Biological Control of Weeds (eds M. H. Julien, R.
Sforza, M. C. Bon, H. C. Evans, P. E. Hatcher, H.
L. Hinz B. G. Rector), pp. 529-538. CSIRO
Entomology, Canberra, Australia.
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Reappraisal!

• Most herbivory on macrophytes is usually by
  specialized oligophagous herbivores

Newman RM 1991 Herbivory and detritivory on
freshwater macrophytes by invertebrates a
review. J. N. Am. Benthol. Soc., 10, 89-114.
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Despite this, only 1 aquatic (alligator weed)
targeted for classical biocontrol in NZ
Agasicles hygrophila damage NZ
Arcola malloi damage, NZ
Effective on floating weed in warmer localities
(ineffective in localities with terrestrial weed
/or winter frosts) Are there other potential
aquatic weed targets in NZ?
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Ranking aquatic weed targets in NZ
We used a recently developed scoring system to
predict cost success of biocontrol of 41
species of NZ aquatic weeds
Paynter Q, Hill R Bellgard S Dawson M. 2009
Improving Targeting of Weed Biological Control
Projects in Australia. Landcare Research Contract
Report LC0809/072.
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SCORING SYSTEM

• Two main categories of factors used to rank
  feasibility of biocontrol
• Biocontrol effort factors (how easy is a
  programme likely to be/how much will it cost?)
• Biocontrol impact factors (how big an impact is
  biocontrol likely to have?)

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Effort scored according to 4 factors

• Target elsewhere. Repeat programs less effort
  vs. new programs - overseas surveys most or all
  host-range testing is already done
• e.g. in NZ, average 53 vs 52 plant spp. used for
  host-range testing repeat novel agents,
  respectively, but for repeat programmes an
  average of only c. 9/53 spp. tested in NZ
• Plant phylogeny. Presence/absence of congeneric
  native/valued crop plants affects the complexity
  duration cost of host-range testing
• Accessibility ease of working in native range.
• Literature regarding natural enemies well
  known/accessible. e.g. UK fauna so well known,
  can prioritise candidate agents for many weeds
  from literature records alone

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Biocontrol impact analytical approach

• Searched biocontrol literature for quantitative
  information regarding
• Impact of biocontrol against weeds in Australia,
  South Africa continental USA (long history of
  weed biocontrol)
• Plant traits of those weeds identified as
  hypothetically important determinants of
  biocontrol success

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Impact factors analytical approach

• Quantitative impact data collected in several
  ways (e.g. cover stems m-2 weed biomass) to
  allow comparison between weeds
• Data converted into proportions dubbed the
  Impact index (I) e.g. If a weed density was
  reduced from 33 to 3.8 stems m-2 then
• Reduction in stem density 3.8-33 -29.2 stems
  m-2

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Impact factors analytical approach

• If multiple data for a weed, an average was
  calculated unless data updated previous studies
• If no biocontrol agents established or anecdotal
  reports of negligible impact biocontrol impact
  assumed to be zero, even if quantitative data
  lacking
• Impact trait data for 72 weed spp.
• Impacts averaged for congeneric weed spp. with
  identical traits reduced number of
  species/genera analysed to 57

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Plant traits correlated to biocontrol impact

• Average biocontrol impact was lower on spp.
  recorded as weeds in the native range
• greater on spp. that reproduce vegetatively

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Plant traits correlated to biocontrol impact

• Average impact was lower against terrestrial
  versus aquatic/wetland species
• greater against biennials/perennials versus
  annuals

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Developing a scoring systemfor biocontrol impact

• Score differentials for traits based on
  quantitative data (e.g. if average biocontrol
  impact was 2x higher for aquatic versus
  terrestrial weeds, it scored 2x more for that
  trait)
• Weighting of traits based on variance explained
  in our analysis. Biocontrol feasibility score was
  scaled to add up to a maximum of 100 points.
• Assume that successes are repeatable, so a target
  that has been successfully controlled in another
  country automatically gets 100 points.

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Developing a scoring systemEcological feasibility
Score lt 50 Difficult targets none achieved an
impact index of -0.6 (but some got close)
Score gt 70 Good targets 94 Impact index between
-0.6 -1
Score 50-70 Medium targets 38 Impact index
between -0.6 -1
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Overall scoring

• The best targets should be the most serious weeds
• We excluded weeds targeted for eradication on a
  national level (unsuitable targets for
  biocontrol)
• We used the Aquatic Weed Risk Assessment Model
  (AWRAM) scores1 for aquatic weed impacts

1Champion, P.D. Clayton, J.S. (2000). Border
control for potential aquatic weeds. Stage 1 Weed
risk model. Science for Conservation 141.
Department of Conservation, Wellington.
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Top ten NZ aquatic weed biocontrol targets
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Top 5 Lythrum salicaria

• Wetland emergent (not strictly aquatic) from
  Europe
• Somewhat limited distribution in NZ (AWRAM score
  may overstate current weed importance, but it is
  proving difficult to control using conventional
  means)
• 81 reduction in weed biomass due to biocontrol
  in USA1

1Katovich, E. J. S., et al. 1999 Effect of
Galerucella spp. on survival of purple
loosestrife (Lythrum salicaria) roots and crowns.
Weed Science, 47, 360-365.
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Lagarosiphon major
Native to South Africa Also a major weed in
Ireland Recent collaboration between Irish S.
African scientists indicates Hydrellia flies
Bagous weevils attack lagarosiphon in S. Africa
are likely to be host-specific1 Host-range
testing is already underway
Photo John Clayton NIWA
1Baars, J. R., et al. (2010) Natural enemies from
South Africa for biological control of
Lagarosiphon major (Ridl.) Moss ex Wager
(Hydrocharitaceae) in Europe. Hydrobiologia, 656,
149-158.
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Egeria densa
Native to South America Also a major weed in USA
Recent native range surveys indicate promising
agents exist including Hydrellia flies1
Host-range testing is already underway
1Cabrera Walsh, G. et al. 2007 Impact of the
natural enemies on the potential damage of
Hydrellia sp. (Diptera Ephydridae) on Egeria
densa. Proceedings of the XII International
Symposium on Biological Control of Weeds, CAB
International Wallingford, UK 353 pp.
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Spartina spp.
Native to Eastern USA (S. alterniflora) Europe
(S. anglica) Prokelisia marginata introduced
from E. USA to west coast invasive species on
Spartina anglica in UK Preliminary results 50
biomass reduction due to biocontrol in the USA1
Photograph Chuan-Kai Ho
1 Grevstad, F. S. et al. 2003 Biological control
of Spartina alterniflora in Willapa Bay,
Washington using the planthopper Prokelisia
marginata agent specificity and early results.
Biological Control, 27, 32-42.
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Lysathia n. sp. reduced Myriophyllum aquaticum
biomass by 60 in South Africa
Cilliers, C. J. (1999) Lysathia n.sp.
(Coleoptera Chrysomelidae), a host-specific
beetle for the control of the aquatic weed
Myriophyllum aquaticum (Haloragaceae) in South
Africa. Hydrobiologia, 415, 271-276.
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Summary

• Biocontrol has been overlooked as a means of
  controlling aquatic weeds in NZ
• Recent developments indicate that some of the
  worst aquatic weeds in NZ are likely to be highly
  amenable to biocontrol
• It is time NZ had an aquatic weeds biocontrol
  programme, like Australia, USA!