Prospects for biocontrol of aquatic weeds in New Zealand

Quentin Paynter & Paul Champion

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 environment”1

• “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.

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.

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.

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.

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.

Agasicles hygrophila damage NZ

Arcola malloi damage, NZ

Despite this, only 1 aquatic (alligator weed) targeted for classical biocontrol in 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?

We used a recently developed scoring system to predict cost & success of biocontrol of 41 species of NZ aquatic weeds

Ranking aquatic weed targets in NZ

Paynter Q, Hill R; Bellgard S; Dawson M. 2009 Improving Targeting of Weed Biological Control Projects in Australia. Landcare Research Contract Report LC0809/072.

SCORING SYSTEM

Two main categories of factors used to rank feasibility of biocontrol:

1. Biocontrol ‘effort’ factors (how easy is a programme likely to be/how much will it cost?)

2. Biocontrol ‘impact’ factors (how big an impact is biocontrol likely to have?)

1.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

2.Plant phylogeny. Presence/absence of congeneric native/valued crop plants affects the complexity & duration [cost] of host-range testing

3.Accessibility & ease of working in native range.

4.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

‘Effort’ scored according to 4 factors:

• Searched biocontrol literature for quantitative information regarding:

1) Impact of biocontrol against weeds in Australia, South Africa & continental USA (long history of weed biocontrol) &

2) Plant traits of those weeds identified as hypothetically important determinants of biocontrol success

Biocontrol impact: analytical approach

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

= -0.885“Impact index” = -29.2 33.0

• 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

Impact factors: analytical approach

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.

Developing a scoring systemEcological feasibility

y = -0.0156x + 0.5774

R2 = 0.4274; P <0.001

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Impact score

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Score > 70Good targets: 94% Impact index between -0.6 & -1

Score 50-70Medium targets: 38% Impact index between -0.6 & -1

Score < 50Difficult targets: none achieved an impact index of -0.6 (but some got close)

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.

Overall score

= AWRAM score

Biocontrol impact score

1Biocontrol effort

score

Top ten NZ aquatic weed biocontrol targets

Weed

Weed Importance

(AWRAM) scoreBiocontrol

Effort scoreBiocontrol

Impact ScoreTotal score

Lythrum salicaria (Purple loosestrife) 54.0 4.0 100.0 1350.0Lagarosiphon major (Oxygen weed) 60.0 12.0 93.0 465.0Egeria densa (Brazilian waterweed) 64.0 13.0 86.0 423.4Spartina anglica; S. alterniflora 54.0 13.0 60.0 249.2Myriophyllum aquaticum (Parrot's feather) 56.0 23.0 100.0 243.5Ceratophyllum demersum (Hornwort) 67.0 28.0 86.0 205.8Vallisneria australis; V. spiralis (eel grass) 51.0 24.0 95.0 201.9Nymphaea mexicana (Mexican water lilly) 47.0 24.0 95.0 186.0Zizania latifolia (Manchurian wild rice) 68.0 34.0 86.0 172.0Elodea canadensis (Canadian pondweed) 46.0 24.0 88.0 168.7

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

Galerucella calmariensis: Linda Wilson, University of Idaho, Bugwood.org

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.

Lagarosiphon major

Photo: John Clayton; NIWA

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 underway1Baars, 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.

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.

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

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.

Photograph: Chuan-Kai Ho

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.

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!